Chapter 11 · Calculating circuit voltages and currents based ... to other electrical systems are covered in Chapter 12 ... PV array DC power generating

2012 Jim Dunlop Solar

Chapter 11

Electrical Integration

Terminology and Definitions Circuit Design Requirements Specifying Electrical Components

Code-Compliant Installation Practices

Presenter

Presentation Notes

The electrical integration of PV systems involves the design and assembly of the various components into a complete power generation unit. The requirements for PV system installations are governed by the National Electrical Code, NFPA 70. References: Photovoltaic Systems, Chap. 11 National Electrical Code, NFPA 70

2012 Jim Dunlop Solar Electrical Integration: 11 - 2

Overview

Identifying key sections of the National Electrical Code applicable to PV system installations.

Classifying typical PV system configurations, their major components and circuits.

Calculating circuit voltages and currents based on component specifications and system designs.

Determining appropriate specifications and ratings for conductors, wiring methods, disconnecting means and overcurrent protection.

Understanding the requirements for PV system grounding.

Presenter

Presentation Notes

Requirements for interactive PV systems and connections to other electrical systems are covered in Chapter 12 – Utility Interconnection. Additional requirements for marking and labeling PV systems and components are covered in Chapter 13 – Permitting and Inspection. Reference: Photovoltaic Systems, p. 285


PV Systems and the National Electrical Code

The National Electrical Code (NEC®) provides for the safety of persons and property relative to the use of electricity. Applies to nearly all electrical installations – notable exceptions include

most vehicles, boats, trains, and certain utility-controlled properties.

Article 690 Solar Photovoltaic Systems Addresses safety standards for the installation of PV systems.

Presenter

Presentation Notes

References: Photovoltaic Systems, p. 286-287 NEC Article 90


PV Systems and the National Electrical Code

Many articles in the first four chapters of the NEC also apply to

PV installations, including but not limited to:

Article 110 Requirements for Electrical Installations Article 230 Services Article 240 Overcurrent Protection Article 250 Grounding and Bonding Article 300 Wiring Methods Article 310 Conductors for General Wiring Article 705 Interconnected Electric Power Production Sources

Presenter

Presentation Notes

Chapters 1-4 of the NEC apply generally to all electrical installations. Chapters 4-6 of the NEC supplement or modify requirements in Chapters 1-4. Other NEC Articles that may apply to PV installations include: Article 314 Outlet, Device, Pull, and Junction Boxes; Conduit Bodies; Fittings; and Handhole Enclosures Article 338 Service-Entrance Cable: Types SE and USE Article 344 Rigid Metal Conduit: Type RMC Article 356 Liquidtight Flexible Nonmetallic Conduit: Type LFNC Article 358 Electrical Metallic Tubing: Type EMT Article 400 Flexible Cords and Cables Article 408 Switchboards and Panelboards Article 445 Generators Article 450 Transformers Article 480 Storage Batteries


Article 690: Solar Photovoltaic Systems

Article 690 Solar Photovoltaic Systems includes nine parts

addressing the following areas of PV installations:

I. General II. Circuit Requirements III. Disconnecting Means IV. Wiring Methods V. Grounding VI. Marking VII. Connection to Other Sources VIII. Storage Batteries IX. Systems Over 600 Volts

Presenter

Presentation Notes

References: Photovoltaic Systems, p. 286-287 NEC Article 90


Photovoltaic Power Source

The PV power source consists of the complete PV array DC power generating unit, including PV source circuits, PV output circuits, and overcurrent protection devices as required.

PV Module

PV Output Circuit

Photovoltaic Power Source

PV Array PV Source Circuits

To disconnect means and DC equipment

Presenter

Presentation Notes

A photovoltaic source circuit includes the circuits and connections between individual PV modules to the point that they are connected together, usually at a combiner box or within an inverter. PV modules are usually connected in series to form source circuits and build voltage (sometimes called strings). Individual source circuits are connected in parallel to build current and power output. A photovoltaic output circuit includes the conductors between the PV source circuits and DC utilization equipment. A photovoltaic power source is the complete DC generating source, including PV source circuits, PV output circuits and associated equipment. Larger PV systems are essentially building blocks of many parallel-connected source circuits and output circuits. References: Photovoltaic Systems, p. 287 NEC 690.2


Interactive PV System Components and Circuits

Interactive System

PV Array

Source Circuit Combiner Box

DC Fused Disconnect

Ground Fault Protection

AC Fused Disconnect

Electric Utility

Utility Disconnect

Integral components in many small string inverters < 12 kW

PV Source Circuits PV Output

Circuit Inverter Input Circuit Inverter Output Circuit

Inverter Main Service Panel

Presenter

Presentation Notes

For simple interactive PV systems, the PV array is connected to the DC input of inverters, and there is no energy storage. The inverter input circuit includes the conductors between the DC photovoltaic output circuits and the inverter DC input terminals. For simple interactive PV systems without energy storage, the PV output circuit is connected to the line terminals of a DC disconnect, and inverter input circuit then runs from the load terminals of the disconnect means to the inverter DC input. The inverter produces AC power based on the array output, only when the array is exposed to sunlight. For interactive-only inverters, the inverter rating and efficiency limits the size of PV array that that can be connected to its DC input. In an interactive system, the PV output circuits and inverter input circuit are essentially the same circuit, separated by a disconnect means. References: Photovoltaic Systems, Chap. 4 NEC 690.2, 690.60, 705


Stand-Alone PV System Components and Circuits

Stand-Alone System

PV Array

Source Circuit Combiner Box

PV Fused Disconnect

Ground Fault Protection

Inverter Fused Disconnect

Auxiliary AC Source

PV Source Circuits

PV Output Circuit Inverter DC input Circuit

Inverter/ Charger

Battery

Charge Controller Battery Fused

Disconnect

Inverter Output Circuit

AC Loads

DC Loads

Presenter

Presentation Notes

For stand-alone PV systems, the inverter input circuit includes the conductors between the inverter and the DC bus containing energy storage, usually a battery. The PV array charges the battery, and the battery provides DC power to the inverter which can produce AC power output at any time. For stand-alone inverters operating from batteries, the inverter ratings limit the size of AC load that can be powered. In addition to energy storage, stand-alone systems may also include additional DC equipment and circuits, such as chargers or rectifiers, charge controllers, DC-DC converters, other DC power sources, and DC load distribution as applicable. References: Photovoltaic Systems, Chap. 4 NEC 690.2, 690.10


Equipment Listing

The listing, labeling and identification of equipment is a foundational basis for building officials in their approval of PV installations for code compliance [90.7, 110.2, 690.4(D)]. Listed equipment has been evaluated to applicable standards by a

Nationally Recognized Test Laboratory (NRTL).

Labels provide recognizable markings, ratings and specifications for listed products, and are used to establish circuit requirements.

Identified equipment is listed and labeled for a specific application, such as for inverters intended for use with utility-interactive systems or with ungrounded PV arrays.

Presenter

Presentation Notes

All equipment used in PV systems must be listed and identified for the application. References: Photovoltaic Systems, p. 350-355, Chap. 13 NEC 690.4(D), 110.2, 90.7


Identification and Grouping

Conductors for PV source circuits and PV output circuits must be

installed in separate raceways from other building circuits unless partitioned [690.4(B), 300.3].

The conductors for PV source circuits, PV output circuits, and inverter circuits must be identified at all terminations and connections. Conductors from multiple PV systems (arrays or inverters) using the same

raceways or junction boxes must also be identified, and grouped by securing together at least every 6 feet if the raceways or junction boxes can be opened. PV source and output circuit conductors shall be routed along structural members.

Presenter

Presentation Notes

Reference: NEC 690.4(B), 300.3


Ground-Fault Protection

Grounded photovoltaic arrays are required to have ground-fault

protection to reduce the potential for arcing and fire hazards [690.5]. Nearly all listed interactive PV inverters incorporate internal array GFP;

when a GF condition is detected, the inverter ceases supplying output power.

The ground-fault protection system detects ground faults,

interrupts the fault current, and provides fault indication.

Markings are required stating that if a ground-fault is indicated, the normally grounded conductors may be energized and ungrounded, presenting a shock hazard.

Presenter

Presentation Notes

Grounded photovoltaic arrays are required to have DC ground-fault protection. This equipment is integral to nearly all utility-interactive inverters, and is intended to detect and interrupt DC ground faults in the array that could create a fire hazard, and ignite combustible materials on a building. Some small systems using ground-mounted PV arrays may be exempted from these requirements, but these arrays may not have more than two parallel source circuits and all DC circuit conductors must be separate from buildings. Array ground fault protection is also not required on non-dwelling units if the equipment grounding conductors are sized for at least two times the ampacity requirements for the circuit conductors, after temperature and conduit fill adjustments have been applied. Ground fault circuits operate by either disconnecting the ungrounded conductor or by disabling the output of inverters or charge controllers if fault currents exceed a certain level. The sensing circuits are 0.5 to 1 A for smaller systems and up to 5 A for larger systems. Typically, a DC-rated fuse or circuit breaker is used for the ground-fault device, and may be installed in different locations in the inverter for either positively or negatively grounded systems. References: Photovoltaic Systems, p. 314-316 NEC 690.5



Lower-voltage system may use

DC circuit breakers for interrupting ground faults.

Presenter

Presentation Notes

Reference: Photovoltaic Systems, p. 314-316



Higher-voltage systems typically use a DC-rated fuse for interrupting ground-fault currents, either externally accessible or located within the inverter.

Presenter

Presentation Notes



DC Arc-Fault Protection

PV systems with DC circuits over 80 volts entering a building are now required to have DC arc-fault protection for the PV array and DC circuits per the 2011 NEC [690.11].

Arc-faults must be detected for any continuity failures between PV

modules, conductors, connectors or terminations.

Arc-fault protection may be provided by disconnecting inverters or charge controllers from the PV array and DC circuits (open-circuit the array), or by using other components in the circuit to interrupt the flow of arcing current.

Requires disconnected equipment or the system to be manually restarted

after the arc fault has been cleared. A visual indicator of an arc-fault condition is also required and must be

manually reset.

Presenter

Presentation Notes

PV systems with DC circuits operating over 80 volts and entering a building are now required to have DC arc-fault protection in the 2011 NEC. Reference: NEC 690.11


Circuit Requirements

The conductors, overcurrent devices, disconnect means and

other equipment used in PV system circuits are selected and sized based on the maximum circuit voltages and currents.

Specifications and ratings for major components, including PV modules and inverters, are required to determine the appropriate circuit parameters for sizing the conductors and wiring systems.

Presenter

Presentation Notes



Maximum PV System Voltage

The maximum system voltage is the PV array open-circuit voltage adjusted for lowest expected ambient temperatures [690.7].

This maximum voltage dictates the minimum voltage ratings for cables, disconnects, overcurrent devices, and other equipment used in the PV source circuits and output circuits.

o

where maximum system voltage (V)

module rated open-circuit voltage at 25 C (V) number of series-connected modules low-temperature correction factor

max oc m T

max

oc

m

T

V V n C

VVnC

= × ×

====

Presenter

Presentation Notes

The rated array open-circuit voltage is multiplied by a temperature correction factor to determine the maximum system voltage. This dictates the minimum voltage ratings for any equipment used in those circuits, including conductors, connectors, disconnects, overcurrent devices, PV modules and inverters. The maximum system voltage must be determined for a specific site and array configuration, and labeled by the installer at or near the DC disconnecting means. For most applications, the maximum systems voltage is limited to 600 V or less, based on maximum voltage limits for PV modules and inverters. References: Photovoltaic Systems, p. 287-288, Chap. 5 NEC 690.7


Voltage Correction Factors

Voltage-temperature correction

factors for crystalline silicon PV modules increase with decreasing temperatures.

Manufacturer’s listed instructions must be used if:

The minimum temperatures are

below -40°C, Other than crystalline silicon PV

modules are used, or Coefficients are provided with listed

instructions.

Minimum Ambient Temperature (oC)

Correction Factor

24 to 20 1.02

19 to 15 1.04

14 to 10 1.06

9 to 5 1.08

4 to 0 1.10

-1 to -5 1.12

-6 to -10 1.14

-11 to -15 1.16

-16 to -20 1.18

-21 to -25 1.20

-26 to -30 1.21

-31 to -35 1.23

-36 to -40 1.25

Adapted from NEC Table 690.7

Presenter

Presentation Notes

Voltage-temperature corrections for crystalline silicon PV modules must use the factors provided in Table 690.7 unless lowest temperatures are below -40°C, or the coefficients are provided with listed module instructions. Traditionally, the site record low temperatures have been used to determine the maximum systems voltage. New guidance in the 2011 NEC suggests using Extreme Annual Mean Minimum Design Dry Bulb Temperatures from the ASHRAE Fundamentals Handbook. This data provides more realistic minimum temperature for determining maximum systems voltage, and minimizes the chances that array voltage will be too low to operate inverters during the hottest operating conditions. References: Photovoltaic Systems, p. 287-288, Chap. 5 NEC 690.7, Table 690.7 Expedited Permit Process for PV Systems: A Standardized Process for the Review of Small-Scale PV Systems, prepared by Bill Brooks for the Solar America Board for Codes and Standards: www.solarabcs.org/permitting (includes annual mean minimum temperatures for selected cities)


Maximum System Voltage: Example 1

Assume the following data for a crystalline silicon module and determine the maximum system voltage: Rated open-circuit voltage of each module is 44.4 VDC. 10 series-connected modules per source circuit. The lowest expected ambient temperature is –25°C (-14°F).

Solution: From Table 690.7, the voltage correction factor is 1.20. Maximum system voltage is (44.4 x 10) x 1.20 = 528 V.

+ -

Presenter

Presentation Notes

References: Photovoltaic Systems, p. 287-288, Chap. 5 NEC 690.7


Maximum System Voltage: Example 2

Using the same data from Example 1, calculate the maximum

system voltage using a manufacturer-supplied voltage-temperature coefficient of -0.33 %/°C.

Solution:

For each module:[ ( )]

44.4 V + [44.4 V × -0.0033/ C × (-25 - 25) C] = 51.7 V

For the entire array:51.7 V per module x 10 modules in series = 517 V.

trans ref ref V cell ref

trans

max

V V V C T T

V

V

= + × × −

=

=

Presenter

Presentation Notes

Recall this calculation from Chapter 5. Compare the maximum system voltage calculated using the manufacturer-supplied temperature coefficient and the results from Table 690.7, which uses a larger temperature coefficient of -0.4%/°C. References: Photovoltaic Systems, p. 132-134, 287-288 NEC 690.7


Maximum Voltage: Dwellings

For one- and two-family dwellings [690.7]:

Maximum PV system voltage is limited to 600 volts.

Live parts in PV circuits over 150 volts to ground must not be accessible to

other than qualified persons while energized.

Presenter

Presentation Notes

For one- and two-family dwellings, the maximum DC voltage for PV array source and output circuits is limited to 600 volts, and live energized parts over 150 volts may not be accessible to other than qualified persons. Some utility-controlled PV installations with restricted access may use array DC voltages up to 1000 V where the PV module ratings permit. References: Photovoltaic Systems, p. 287-288 NEC 690.7


Maximum PV Circuit Currents

Maximum PV source circuit currents are calculated by

multiplying their short-circuit current by 125% [690.8(A)].

This 125% factor is in addition to the 125% factor required by 690.8(B), and accounts for higher than rated current output from PV arrays exposed to irradiance levels above 1000 W/m2.

The maximum PV output circuit current is the sum of parallel-connected source circuit currents.

Presenter

Presentation Notes

Calculating the maximum circuit currents is the first step in determining requirements for sizing conductor ampacity and overcurrent protection. The maximum PV source circuit currents are determined by multiplying the short-circuit current of the source circuit by 125%. When PV source circuits consist of only series-connected modules, the short-circuit current for the source circuit is the same as for a single module. If parallel connected modules are used in source circuits, the source circuit maximum current is the short-circuit current of an individual module multiplied by the number of parallel-connected modules. This 125% factor is required to account for the fact that PV modules can produce more than their rated short-circuit currents for continuous periods during the middle of the day, especially at high altitudes and on very clear days when the solar irradiance may exceed 1000 W/m2 for several hours. References: Photovoltaic Systems, p. 289-290 NEC 690.8(A)


Determine the maximum currents for a PV array consisting of 4 parallel strings of 10 series-connected PV modules each. The PV module rated short-circuit current (Isc) is 5.3 A.

The source circuit maximum currents are: Isc x 1.25 = 5.3 A x 1.25 = 6.63 A

The output circuit maximum current is:

4 parallel source circuits x 6.63 A = 26.5 A

Maximum PV Circuit Currents: Example

PV Source Circuits

PV Output Circuit

Presenter

Presentation Notes

PV output circuits consist of one or more parallel connected source circuits. The maximum PV output circuit currents are determined by multiplying the source circuit maximum current by the number of parallel source circuits. References: Photovoltaic Systems, p. 289-290 NEC 690.8(A)


Inverter Output Circuit Current

For both stand-alone and interactive systems, the maximum inverter output current is the inverter continuous output current rating, and is usually marked on inverter labels.

For unity power factor inverters, the maximum output current can be estimated by dividing the rated AC power output by the nominal AC output voltage.

For example, consider an inverter rated for 6 kW maximum

continuous AC power output at 240 V. The maximum output current is: 6000 W / 240 V = 25 A.

Presenter

Presentation Notes

The maximum inverter current for either stand-alone or interactive inverters is the continuous output current rating from the inverter nameplate label. The maximum current can also be calculated for unity power factor inverters by dividing the maximum rated power output by the AC output voltage. References: Photovoltaic Systems, p. 289-290 NEC 690.8(A)


Inverter Input Circuit Current

For interactive systems, the inverter input circuit is the same as

the PV output circuit, and has the same maximum current.

For stand-alone inverters operating from batteries, the maximum inverter input current must be evaluated at the lowest operating voltage when the inverter is producing rated power:

=

where = maximum inverter input current (A) = rated inverter maximum AC power output (W) = minimum inverter operating voltage (V) = inverter efficiency

ACmax

min inv

max

AC

min

inv

PI V

IPV

η

η

×

Presenter

Presentation Notes

For stand-alone systems, the inverter input current increases with decreasing battery voltage for the same output power level, and must be considered in determining the maximum input current. The maximum input current can be calculated by dividing the maximum rated power output of the inverter by the product of the lowest operating battery voltage and rated efficiency of the inverter. References: Photovoltaic Systems, p. 289-290 NEC 690.8(A)


Inverter Input Circuit Current: Stand-Alone Inverters

Consider a nominal 48 V, 4000 W stand-alone inverter that is 90%

efficient, and operates to a low voltage cutoff of 44 V.

The maximum inverter input circuit current is:

4000 W = 101 A44 V 0.9

ACmax

min inv

PI V η

= =× ×

Presenter

Presentation Notes

The resulting inverter input circuit current is nearly 10% higher than would be calculated using the nominal inverter voltage. References: Photovoltaic Systems, p. 289-290 NEC 690.8(A)


Overcurrent Device Ratings

Overcurrent devices in PV system circuits must be sized for at least 125% of the maximum circuit currents [690.8(B)]. For PV source circuits and PV output circuits, this 125% factor is in

addition to the 125% factor used to calculate maximum circuit currents in 690.8(A), and results in a combined factor of 125% x 125% = 156%.

The next higher standard size overcurrent protection device may be used.

Overcurrent devices used in PV source circuits must be no

greater than the maximum allowable overcurrent device (or fuse) rating on the module label.

Presenter

Presentation Notes

Overcurrent devices in PV system circuits must be sized to carry at least 125% of the maximum circuit currents calculated in 690.8(A). References: Photovoltaic Systems, p. 289-290 NEC 690.8(B), 240.4, 240.6


Overcurrent Device Ratings

The temperature ratings for terminals and overcurrent devices

may limit the ampacity of connected conductors.

The conductor ampacity is selected at a temperature rating no greater than the temperature ratings of a terminal or device that it is connected to.

Using terminals rated for 90°C usually avoids this concern, and the 90°C conductor ampacities may be used.

Presenter

Presentation Notes

If overcurrent devices are operated over 40°C, manufacturer’s temperature correction factors must be used to determine the overcurrent device rating. References: Photovoltaic Systems, p. 289-290 NEC 690.8(B), 110.3(B), 110.14(C)


Conductor Ampacity

Conductors in PV system circuits must be sized for the greater of the following:

125% of the maximum circuit current without adjustments for conditions of

use, or

The maximum circuit current adjusted for conditions of use.

Overcurrent devices, where required, must protect the conductors based on their allowable ampacity after adjustments for conditions of use.

Conditions of use, namely temperature and conduit fill deratings, often account for more than 20% reduction in allowable conductor ampacity.

Presenter

Presentation Notes

References: Photovoltaic Systems, p. 289-290 NEC 690.8(B)


Sizing Overcurrent Devices: PV Source and Output Circuits

Consider a PV array with 4 parallel-connected source circuits having a maximum current of 6.6 A for each source circuit.

The minimum required overcurrent device rating for the PV array source circuits is: 6.6 A x 1.25 = 8.3 A The next higher standard overcurrent device rating is 9 A, or may be as

high as the module maximum overcurrent device rating allows.

For the PV output circuit: 8.3 A x 4 parallel source circuits = 33.1 A The next higher standard size overcurrent device is 35 A.

Presenter

Presentation Notes

Continuation of previous example. References: Photovoltaic Systems, p. 289-290 NEC 690.8, 690.9


Sizing Overcurrent Devices: Inverter Output Circuit

For an inverter with maximum continuous output current of 25 A,

the minimum overcurrent device rating must be at least: 25 A x 1.25 = 31.3 A

The overcurrent device rating must also be no greater than the maximum overcurrent device rating on the inverter label if marked.

Presenter

Presentation Notes

Continuation of previous example. References: Photovoltaic Systems, p. 289-290 NEC 690.8, 690.9


Conductor Ampacity

Allowable conductor ampacity is determined by conductor properties and conditions of use:

Material type (copper or aluminum) Cross sectional area, or gage size (AWG) Insulation temperature rating Location (ambient temperature, in free air, conduit or buried, on rooftops,

or with other conductors)

Ampacity decreases with increasing conductor temperature. Rated ampacities at 30°C are adjusted by a derating factor for higher

temperatures.

Presenter

Presentation Notes

PV modules can operate at temperatures up to 80°C in warm climates. Conductors with insulation types rated for at least 90°C should be used, and their ampacity adjusted accordingly. References: Photovoltaic Systems, p. 290-298 NEC Table 310.16, Table 310.17, Chap. 9 - Table 8


Allowable Ampacities

Tables 310.15(B)(16) and 310.15(B)(17) in the NEC give allowable ampacities at 30°C for insulated conductors rated up to 2000 volts for insulation temperature ratings of 60°C, 75°C and 90°C. Adjustment factors are applied to derate allowable ampacities for

maximum operating temperatures greater than 30°C [Table 310.15(B)(2)(a)].

Table 310.15(B)(16) applies to no more than three current-

carrying conductors in a raceway, cable, or directly buried. Adjustments are applied to derate allowable ampacities when more than

three current-carrying conductors are installed in a single conduit or raceway [Table 310.15(B)(3)(a)].

Table 310.15(B)(17) applies to conductors installed in free air, not in conduit or raceways.

Presenter

Presentation Notes

References: Photovoltaic Systems, p. 290-298 NEC 310, Table 310.15(B)(16), Table 310.15(B)(17)


More Than Three Conductors in Conduit

When more than three current-

carrying conductors are installed in a single conduit or raceway, the conductor ampacity must be derated accordingly [310.15(B)(3)(a)].

For example, if 10 to 20 current-carrying conductors are installed in a single conduit, the ampacity for each conductor is reduced by 50 percent.

Number of Current-Carrying

Conductors

Percentage Adjustment

4-6 80

7-9 70

10-20 50

21-30 45

31-40 40

41 and above 35

Adapted from NEC Table 310.15(B)(2)(a)

Presenter

Presentation Notes

Allowable conductor ampacity is reduced when more than three current-carrying conductors occupy the same conduit or raceway. References: Photovoltaic Systems, p. 290-298 NEC 310.15, Table 310.16, Table 310.15(B)(3)(a)


Rooftop Conductors in Conduit

PV source circuit and PV output circuit conductors installed in

conduit on a roof exposed to direct sunlight experience very high operating temperatures, and conductor ampacities must be adjusted accordingly [310.15(B)(3)(c)].

Conductor temperatures in conduits are based on the distance from the bottom of the conduit to the roof surface, and requires adding and specified temperature rise to the maximum expected ambient temperature. The resulting conductor temperature is then used in conjunction with

Table 310.15(B)(2)(a) to determine the allowable conductor ampacity.

Presenter

Presentation Notes

Where conductors or cables are installed in conduits exposed to direct sunlight on or above rooftops, temperature corrections are based on the height of the conduit from the roof surface. For example, the temperature of conductors in a rooftop conduit exposed to direct sunlight that is located ½ inch to 3-½ inches above a roof surface has a temperature adder of 22°C. For a maximum ambient temperature of 40°C, the ampacity adjustment must be made from Table 310.15(B)(2)(a) for the conductor operating at 62°C. References: NEC 310.15, Table 310.15(B)(3)(c), Table 310.16 Expedited Permit Process for PV Systems: A Standardized Process for the Review of Small-Scale PV Systems, prepared by Bill Brooks for the Solar America Board for Codes and Standards: www.solarabcs.org/permitting (includes mean maximum temperatures for selected cities).


Allowable Ampacity: Example

Consider a 12 AWG 90°C-rated conductor (USE-2 or PV Wire) with

a rated ampacity of 30 amps (wet or dry) at ambient temperatures of 26-30°C.

If eight (8) current-carrying conductors (4 source circuits) are installed in a single conduit, the allowable ampacity for the conductor is reduced to:

30 A x 0.7 = 21 A

Presenter

Presentation Notes

References: Photovoltaic Systems, p. 290-294 NEC Table 310.15(B)(2)(a), Table 310.15(B)(2)(c), Table 310.15(B)(16)


Allowable Ampacity: Example (cont.)

If these conductors are installed in conduit mounted flush to a

roof surface that is exposed to direct sunlight, the ambient temperature adder is 33°C from Table 310.15(B)(2)(c).

If the maximum ambient temperature is 35°C, the conductor ampacity must be determined at 35 + 33 = 68°C.

For a 90°C conductor, the temperature correction factor is 0.58, which further reduces the allowable ampacity to:

21 A x 0.58 = 12.2 A

Presenter

Presentation Notes

Under these conditions of use, this exceeds the minimum conductor ampacity required for the source circuits in the preceding example (8.3 A). References: Photovoltaic Systems, p. 290-294 NEC Table 310.15(B)(2)(a), Table 310.15(B)(2)(c), Table 310.15(B)(16)


Overcurrent Protection

All PV system circuits must be protected from overcurrent in accordance with Article 240 [690.9]. Overcurrent protection for PV source and output circuits is usually not

required for small interactive systems using only one or two identical strings.

Branch-circuit or supplementary-type overcurrent devices are

permitted to provide overcurrent protection for PV source circuits, and are required to be accessible, but not required to be readily-accessible. A single overcurrent device is used to protect series-connected strings of

two or more modules, and must have a DC rating.

Presenter

Presentation Notes

Overcurrent protection is not required in PV source circuit or PV output circuits for single-string interactive inverters, where there are 1) no external sources such as parallel-connected source circuits, batteries, or backfeed from inverters, or 2) the short-circuit currents from all sources do not exceed the ampacity of the conductors. Normally, two identical strings in parallel are also permitted. A single overcurrent device protects the all PV modules and conductors in a source circuit. Branch-circuit or supplementary-type overcurrent devices are available in one ampere size increments from 1 A to 15 A, allowing a device rating to be selected close to the module maximum overcurrent device rating allowed. Source circuit fuses or circuit breakers must be accessible for service, but may be located on rooftops or behind PV arrays in combiner boxes. Fuses or circuit breakers used in any PV system DC circuits must be listed for the appropriate voltage, current, and interrupt ratings. References: Photovoltaic Systems, p. 289-290 NEC 690.9, 240.6


Voltage Drop

Voltage drop should be limited in all PV system circuits to no

more than 2 to 3%.

Excessive voltage drop in DC circuits is a particular concern for lower-voltage systems and for PV arrays located long distances from DC utilization equipment.

Excessive voltage drop in AC circuits may cause loads to operate improperly, or hinder an interactive inverter’s ability to remain connected to the grid.

Presenter

Presentation Notes



Voltage Drop

Conductor resistance and voltage drop increase with smaller

conductor size, longer conductor lengths, and higher operating currents and temperatures.

Ohm’s law is used to calculate voltage drop:

where = voltage drop (V)

= operating current (A) = conductor resistance per unit length ( /kft.)

= total conductor round-trip length (kft)

drop op C

drop

op

C

V = I R L

V IRL

× ×

Ω

Presenter

Presentation Notes



Voltage Drop

Consider a PV array that operates nominally at 500 V with a maximum output current of 20 A. The output circuit used 8 AWG stranded conductors having resistance of 0.8 Ω/kft, and the one-way circuit distance is 350 feet.

The voltage drop is this circuit is:

Based on the nominal system operating voltage of 500 V, this voltage drop amounts to: 11.2 V / 500 V = 0.0224 or 2.2%

0.8Ω (2×350)20 A × × kft = 11.2 Vkft 1000

drop op C

drop

V = I R L

V

× ×

=

Presenter

Presentation Notes

Make sure to use to entire round-trip circuit length for voltage drop calculations. If the system operating voltage were only 250 volts, this amount of voltage drop would be double the percentage of the nominal circuit voltage. Reference: Photovoltaic Systems, p. 294-295


Disconnecting Means

All ungrounded current-carrying DC conductors of a PV system

require a disconnecting means to isolate these circuits from all other conductors in a building or structure [690.13].

A switch must not be installed in the circuit with a grounded conductor, unless:

The switch is part of an arc-fault or ground-fault protection circuit, or The switch is only used for maintenance, accessible only to qualified

persons, and rated for the maximum DC voltage and current in the circuit.

Presenter

Presentation Notes

Article 690, Part III covers the requirements for disconnecting means in PV systems. References: Photovoltaic Systems, p. 309-310 NEC 690.13


Disconnecting Means

The following provisions also apply to the disconnecting means for PV output circuits [690.14]: Not required to be service-rated equipment or installed at the array

location.

Source circuit switches and overcurrent devices are permitted on the PV array side of the disconnecting means.

A maximum of six (6) disconnects are allowed, and they must be grouped,

suitable for use, and each marked to identify it as a PV system disconnect.

Must be installed at a readily-accessible location outside a building or inside a building nearest to the point where the conductors enter the building.

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Presentation Notes

The PV disconnecting means is located in the PV output circuit. Exceptions allow other locations inside a building for the PV DC disconnect when the conductors are routed in metal conduit or type MC cable. References: Photovoltaic Systems, p. 309-310 NEC 690.14, 690.17, 690.31(E)


Disconnecting Means

Utility-interactive inverters

installed in not-readily-accessible locations, such as in attics or on rooftops, must have AC and DC disconnecting means located within sight of or inside the inverter [690.14(D)].

An additional, readily-accessible AC disconnecting means is also required.

A plaque or directory must be installed at the service entrance denoting the presence of a PV power source and the inverter location.

Presenter

Presentation Notes

Reference: NEC 690.14(D), 705.10


Disconnecting Means

All PV system equipment must have a means to disconnect from ungrounded conductors from all sources. The disconnecting means must be grouped and identified if equipment can be energized from more than one source [690.15]. These disconnect requirements apply to PV arrays, charge controllers,

batteries, inverters and chargers. Single AC disconnecting means are permitted for one or more AC

modules or micro inverters.

Switches or circuit breakers used for the disconnecting means must be [690.17]: Readily accessible. Manually and externally operable, and protected from live parts. Plainly indicating an open or closed position. Rated for sufficient fault current interrupting and maximum system voltage.

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Presentation Notes

All PV system equipment must be isolated from all supply sources for service and maintenance. Reference: Photovoltaic Systems, p. 309-310 NEC 690.15, 690.17


Disconnecting Means

Warning signs are required when

both sides of a disconnecting means may be energized in the open position.

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Presentation Notes

PV system DC disconnects in interactive systems are energized on one side from the PV array, and on the other side from residual voltage on inverter input circuit capacitors, for several minutes after the disconnect has been opened and the inverter turned off. Reference: Photovoltaic Systems, p. 309-310 NEC 690.17


DC Disconnects

This combination DC disconnect and combiner box from SMA mounts to the bottom of the inverter, and allows the connection of up to four fused source circuits. It also includes a partitioned raceway for the inverter AC output conductors.

Presenter

Presentation Notes

Reference: Photovoltaic Systems, p. 309-310 NEC 690.15, 690.17


DC Disconnects

A maximum of six (6) disconnects are allowed for the PV power

source, and they must be grouped and marked as PV disconnects [690.14].

Presenter

Presentation Notes

Reference: Photovoltaic Systems, p. 309-310 NEC 690.14


Fuses

Fuses used in PV source circuits must be able to be disconnected independently of other source circuit fuses [690.16].

Fuses must have disconnects to isolate them from both sides if so energized.

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Presentation Notes

Fuse pull-outs or holders that are not load-break rated must not be used to disconnect fuses under load, and a separate load-break rated disconnect means is required. PV output circuits must have disconnect means within 6 feet of fuses if fuses cannot be isolated from energized circuits. If more than 6 feet, a directory identifying the disconnect locations is required. Reference: Photovoltaic Systems, p. 309-310 NEC 690.16


Installation and Service of PV Arrays

Because PV arrays are always energized when exposed to light,

arrays or portions of arrays are disabled for installation or maintenance by open-circuiting, by short-circuiting, or by placing an opaque covering over the array [690.18].

Where covering arrays is impractical, the array may be sectioned into lower-voltage and less hazardous portions by opening series connectors until the installation or maintenance is completed.

Presenter

Presentation Notes

Reference: NEC 690.18


Wiring Methods

Wiring methods used in PV systems include standard types of

conductors, raceways and fittings used in building electrical systems, in addition to special cables, connectors and other methods specifically identified for use in PV systems [690.31].

Environmental exposure requires PV array conductors to have insulation rated for high temperatures, wet locations, and sunlight resistance.

Presenter

Presentation Notes

PV array wiring methods and materials are subjected to harsh environmental conditions, and must have appropriate ratings for the application. Reference: NEC 690.31


Conductor Properties

Electrical conductor properties are defined by [310]:

Type of material (aluminum, copper-clad aluminum or copper)

Size of conductor in AWG or kcmils

Stranded or single conductor (8 AWG and larger must be stranded)

Insulation type (single or double-insulated, single-conductor or multi-

conductor cable with outer insulation)

Insulation material (thermoplastic, thermoset, silicone, etc.)

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Presentation Notes

PV source circuit and output circuit conductors are installed in wet locations. Conductors appropriate and listed for use in wet locations include types MTW, RHW, RHW-2, TW, THW, THW-2, THHW, THWN, THWN-2, XHHW, XHHW-2 and ZW. Most PV source circuit conductors are exposed to direct sunlight, and must be rated and marked as sunlight resistant. All conductors must be insulated unless otherwise permitted to be bare, for example, with equipment grounding conductors. Conductors sizes 8 AWG and larger installed in raceways must be stranded. Conductor sizes 1/0 AWG and larger only are permitted to be connected in parallel, and additional requirements apply. Conductors used for direct-burial applications must be identified for the use. The minimum size of conductors for electrical systems operating 0 to 2000 volts is 14 AWG copper, or 12 AWG aluminum or copper-clad aluminum. Reference: Photovoltaic Systems, p. 290-302 NEC 310


Conductor Types

Two types of single-conductor cables are permitted to be used for exposed connections between PV modules within PV array source circuits [690.31]: USE-2 is rated for 90°C wet or dry, 600 volts, and is sunlight resistant.

Photovoltaic (PV) wire is a double-insulated sunlight-resistant conductor

rated for 90°C in wet locations, and for 600, 1000 or 2000 volts. PV wire is intended for use with higher voltage and ungrounded PV arrays.

Other standard types of conductors rated for 90°C and wet

locations are not sunlight resistant, and must be installed and protected in conduit or other raceways, including types:

RHW-2, THW-2, THHW-2, THWN-2 and XHHW-2

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Presentation Notes

Single exposed conductor are not permitted to transition from PV modules and arrays any distance to source circuit combiner boxes. A junction box should be used to transition the exposed wiring to a raceway system immediately upon leaving the array location. References: Photovoltaic Systems, p. 290-304 NEC 690.31, 300, 310


Wiring Methods

Single, exposed conductors are not permitted to run distances from PV modules to source circuit combiner boxes.

Single conductors must be installed in conduit upon leaving the PV array location.

Presenter

Presentation Notes

References: Photovoltaic Systems, p. 290-304 NEC 690.31(B)


Photovoltaic (PV) Wire

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Presentation Notes

Listed and labeled photovoltaic (PV) wire is allowed for exposed outdoor locations for photovoltaic module source circuit interconnections within the photovoltaic array, and provided with factory-installed leads on many PV modules. Exposed single-conductor wiring is only permitted for module interconnections within PV array source circuits, and must transition to other approved wiring methods and raceway systems at junction boxes at the array. The wiring must be neatly tied and concealed beneath the array to prevent movement, chaffing or other damage to the conductors or connectors. References: Photovoltaic Systems, p. 290-304 NEC 690.31(B), 110.12


USE-2 Single Conductor Cables

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Presentation Notes

USE-2 conductors are sunlight-resistant and rated for 90°C in wet locations. Transitions for exposed conductors to junction boxes or raceways must use appropriate fittings, connectors or strain reliefs. Reference: NEC 690.31(B), 300, 310, 338


Conductor Colors

Grounded current-carrying conductors must be white, gray or

have three white stripes or white markings at terminations on conductors larger than 6 AWG. Can not be green colored.

Equipment grounding conductors (EGC) must be bare, or have

insulation colored green or green with yellow stripes.

Ungrounded current-carrying conductors can be any color except for green, white or gray to clearly distinguish them as ungrounded conductors.

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Presentation Notes

In a grounded system where one current-carrying conductor is grounded, the insulation on all grounded conductors must be white, gray or have three white stripes or be any color except green if marked with white plastic tape or paint at each termination (marking allowed only on conductors larger than 6 AWG). Conductors used for module frame grounding and other exposed metal equipment grounding must be bare (no insulation) or have green or green with yellow-striped insulation color. Any insulated equipment-grounding conductor used to ground PV module frames must be rated for wet locations and sunlight-resistance, such as USE-2. There is no NEC requirement designating the color of the ungrounded conductor, but the convention in ac power wiring is that the first two ungrounded conductors are colored black and red. This suggests that in two-wire, negative-grounded PV systems, the positive conductor could be red or any color with a red marking except green or white, and the negative grounded conductor must be white. References: Photovoltaic Systems, p. 290-304 NEC 310.12, 200.6, 200.7, 210.5, 250.119


Terminating Conductors

The following are basic requirements for terminating electrical conductors [110.3, 110.14]: All terminating devices must be listed and identified for the proper

conductor material, the conditions of use, and installed according to manufacturer’s instructions.

Conductors or materials made of dissimilar metals must not be allowed to touch each other, and any solders or corrosion inhibitors used must be suitable for the application.

The ampacity of any connected conductors must be evaluated at the lowest termination temperature rating.

Crimped lugs must use the proper crimping tool. Terminals using setscrews must be torqued to the proper specifications. Fine-stranded cables require special terminals intended for the use.

Presenter

Presentation Notes

References: Photovoltaic Systems, p. 290-304 NEC 110.3, 110.14,


Conductor Protection

For PV systems with a maximum system voltage over 30 volts, PV

source and output circuit conductors must not be readily accessible for physical protection and to reduce electrical hazards [690.31]. Requires conductors to be installed in conduit, enclosures or other

raceways.

The conductors must be made not readily accessible by elevation, fencing around the array, or guarding of the exposed conductors with barriers.

Presenter

Presentation Notes

This requirement applies to any PV installation operating at nominal DC voltages of 24 volts and higher, which would have a maximum system voltage greater than 30 volts. Reference: NEC 690.31


Conductor Protection

Ground-mounted PV arrays are often elevated or installed behind fencing to make exposed conductors not readily accessible.

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Presentation Notes

Roof-mounted PV arrays offer protection for exposed conductors by elevation and limited access. Make sure to leave sufficient spacing between the fencing and array to avoid shading. Usually, this requires the east, south and west parts of an array to be 2 to 3 times as far away as the fence height. Reference: NEC 690.31(A)


Small-Conductor Cables

Smaller conductor sizes 16 AWG and 18 AWG are often used on

higher-voltage, lower-current thin-film PV modules for source-circuit module connections [690.31(D)]. These cables must meet the PV source circuit ampacity requirements

after temperature derating, and be rated for sunlight resistance and wet locations.

Normal listing and labeling marks used on conductor sizes 14 AWG and larger are not usually printed on smaller conductor cables.

Presenter

Presentation Notes

Single-conductor cables listed for outdoor use that are sunlight resistant and moisture resistant in sizes 16 AWG and 18 AWG are permitted to be used for source circuit module connections. References: Photovoltaic Systems, p. 290-302 NEC 690.31(D)


DC Wiring Inside Buildings

PV source circuits and PV output circuits inside a building are required to be routed in metal raceways, metal enclosures, or use type MC metal-clad cable prior to the first readily accessible disconnect means [690.31(E)].

Conductors and wiring methods are not permitted within 10 inches under a roof deck unless the location is underneath PV modules or equipment.

Conductors and raceways for PV circuit conductors inside

buildings must be marked and routed along structural members where possible.

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Presentation Notes

Special requirements apply to DC PV source circuit and output circuit conductors inside a building. These conductors may be run through walls and attics and physical protection is required. Certain markings, labels and permitted locations apply to these DC conductors and wiring methods. References: Photovoltaic Systems, p. 297 NEC 300, 310, 330, 690.4(B), 690.31(E)


Locations for PV Array Wiring and Disconnects

PV Array

Metal conduit or cable is not required where the PV disconnect is located outside a building (A) or nearest to the point where the conductors enter a building (B). .

Where PV conductors run inside a building before reaching the disconnect, metal conduit or type MC cable must be used.

PV disconnect

PV Disconnects

A B

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Presentation Notes

Direct-current PV source and output circuits inside a building must be contained in metal raceways, metal enclosures, or use type MC cable from the point of penetration of the surface of the building or structure to the first readily accessible disconnecting means. This provides additional physical protection and fire resistance for these circuits should faults develop in the cable, and they also provide an additional ground-fault detection path. References: Photovoltaic Systems, p. 297 NEC 300, 310, 330, 690.4(B), 690.31(E)


Flexible Cables

Flexible cords and cables may be used for tracking PV arrays,

and must be identified for hard service, outdoor use, wet locations and sunlight resistance [690.31(C)].

Temperature correction factors to be used are listed in Table 690.31(C).

Terminals, lugs, devices, or connectors must be specifically identified and listed for used with fine-stranded flexible cables [690.31(F)].

Presenter

Presentation Notes

References: Photovoltaic Systems, p. 297 NEC 110.14, 400, 400.5, 690.31(C), 690.31(F), Table 690.31(C)


Component Interconnections

Concealed fittings and connectors are permitted for module

connections that are listed and identified for the use, and properly rated for the circuit requirements and environmental conditions [690.32].

Applies to building-integrated PV products.

Presenter

Presentation Notes

Concealed connectors and fittings are used with many type of building-integrated PV modules and arrays. References: NEC 690.32


Connectors

Connectors are used in PV systems for PV module connections and other equipment as applicable, and must be [690.33]:

Polarized and non-interchangeable.

Guarded against contact with live parts.

Latching or locking type.

• Readily accessible connectors operating at over 30 volts require a tool for opening.

First to make and last to break grounded conductors.

Load-break rated for interrupting the maximum circuit current, or require a

tool for opening and marked “Do Not Disconnect Under Load” or “Not for Current Interrupting.”

Presenter

Presentation Notes

For PV arrays operating above 30 volts, the connectors must be polarized, guarded, non-interchangeable, latching or locking type, and require a tool for opening if they are not load-break rated. The connectors must also be weathersealed and otherwise appropriate for the conditions of use (outdoor and wet locations). Special connector mating and crimping tools are required for their fabrication and assembly with conductors. References: Photovoltaic Systems, p. 298-300 NEC 690.33


Module Connectors

Multi-Contact MC4 connectors with locking sleeve and assembly/opening tool.

Presenter

Presentation Notes

References: Photovoltaic Systems, p. 298-300 NEC 690.33


Module Connectors

Tyco SOLARLOK connectors on PV module whips.

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Presentation Notes



Junction Boxes

Junction boxes and other enclosures are used in PV systems to

combine circuit conductors, provide transitions for wiring methods, and to protect electrical equipment and devices from physical damage and the environment [690.34].

Junction boxes may be installed behind or beneath PV arrays, and requires them to be made accessible by removal of modules connected to a flexible wiring system. PV source circuit combiner boxes must be listed to the UL 1741 standard.

Presenter

Presentation Notes

The size and ratings of conduit and junction boxes used in PV systems is based on the normal requirements for all electrical systems covered in Chapter 3 of the NEC. In many cases, the installer must select and specify the appropriate raceways and junction boxes for the given application. PV source circuit combiner boxes must be listed and identified assemblies under UL 1741. References: Photovoltaic Systems, p. 301-302 NEC 690.34


Enclosure Classifications

Electrical enclosures for non-hazardous are classified for the

level of protection they provide from the elements and physical damage [110.20]. Enclosure types 1, 2, 5, 12, 12K and 13 are for indoor use only. Enclosure types 3, 3R, 3S, 4, 4X, 6 and 6P are for both indoor and

outdoor use and provide varying degrees of protection from dust, water and corrosion.

Enclosures must be installed according to instructions to

maintain its classification.

Presenter

Presentation Notes

References: Photovoltaic Systems, p. 301-302 NEC 110.20 UL 50/50E Enclosures for Electrical Equipment


Source Circuit Combiner Boxes

Source circuit combiner boxes are used to parallel multiple PV source circuits and transition to the PV output circuit wiring [690.34]. Source circuit combiners include touch-safe fuses for source circuit overcurrent

protection and the module listing.

Load-break rated DC disconnects or circuit breakers at the combiner box level permit isolation of subarrays for maintenance, testing and emergency events.

Advanced combiner boxes intended for use with specific inverters may include DC-DC converters and maximum power point trackers.

Source circuit combiners must be UL1741 listed and rated for enclosure

type, number of poles, conductor sizes and terminal temperatures.

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Presentation Notes




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Presentation Notes



Combiner Boxes

Blue Oak PV Products

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Presentation Notes




Cooper Bussmann

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Presentation Notes



Ungrounded Systems

PV arrays are permitted to have ungrounded source and output circuits when the following conditions are met [690.35]: Both ungrounded conductors (positive and negative) must have a

disconnecting means and overcurrent protection. Array ground fault-protection for all conductors must be provided. All PV source and output circuit conductors must be either:

• Installed in raceways, or • Jacketed multi-conductor cables, or • Listed and labeled PV wire where used for single-conductor exposed

PV module connections.

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Presentation Notes

Inverters or charge controllers used with ungrounded PV arrays must be listed and identified for such use. The PV power source must be marked at each disconnect, junction box or other device that may be serviced with the following label: “WARNING - ELECTRIC SHOCK HAZARD. THE DIRECT CURRENT CIRCUIT CONDUCTORS OF THIS PHOTOVOLTAIC POWER SYSTEM ARE UNGROUNDED BUT MAY BE ENERGIZED WITH RESPECT TO GROUND DUE TO LEAKAGE PATHS AND/OR GROUND FAULTS.” References: Photovoltaic Systems, p. 317-318 NEC 690.35


Grounding and Bonding

Proper grounding of PV systems reduces the risk of electrical shock to personnel and the effects of lightning and surges on equipment.

Presenter

Presentation Notes

Proper grounding of PV systems reduces the risk of electrical shock to personnel and the effects of lightning and surges on equipment. There are two basic types of grounding. System grounding connects a current-carrying conductor in an electrical system to ground, or earth potential. Equipment grounding connects non-current carrying metal parts to ground, such as PV module frames, racks, enclosures, junction boxes, conduit and other metallic components. All PV systems require equipment grounding, and most also require system grounding. The grounding and bonding requirements for PV systems are covered in Article 690 Part V and Article 250. References: Photovoltaic Systems, p. 311-320 NEC 100, 250, 690 Part V


System vs. Equipment Grounding

System grounding is the intentional connection of a current-

carrying conductor in an electrical system to ground (earth). Commonly, this connection is made at the supply source, such as a

transformer or at the main service disconnecting means for a premises.

Equipment grounding is the connection of non-current carrying metal parts to ground. Requires electrical bonding and grounding of PV module frames, racks,

enclosures, junction boxes, conduit and other metallic components.

System grounding and equipment grounding conductors are separate and only connected together (bonded) at the source of supply.

Presenter

Presentation Notes

There are two basic types of grounding. System grounding connects a current-carrying conductor in an electrical system to ground, or earth potential. Equipment grounding connects non-current carrying metal parts to ground, such as PV module frames, racks, enclosures, junction boxes, conduit and other metallic components. Most PV systems require system and equipment grounding. Article 100 of the NEC defines specific terms associated the grounding and bonding of electrical systems. Refer to diagrams and illustrations in the NEC Handbook for examples. References: Photovoltaic Systems, p. 311-320 NEC 100, 250, 690.43


System Grounding

Any PV power source with a maximum voltage over 50 V must

have one current-carrying conductor grounded [690.41]. Exceptions are permitted for ungrounded systems meeting specific

requirements.

The connection of the grounded DC system conductor must be made at a single point in the PV output circuit [690.42].

For interactive systems, the connection for the grounded DC current-

carrying conductor is typically made only at the ground-fault protection device internal to the inverter, and may be required for proper operation of the ground-fault protection device.

Presenter

Presentation Notes

One conductor of a 2-wire system, or the center tap conductor of a bipolar system must be grounded if the maximum PV system voltage is over 50 volts. The DC system grounding connection must be made at a single point on the PV output circuit. Locating this connection point as close as practicable to the photovoltaic source better protects the system from voltage surges due to lightning. Typically, for PV systems requiring ground-fault protection, the single point of connection for a DC current-carrying conductor is made internal to a ground-fault protection device or utility-interactive inverters, and additional external bonding connections are not permitted. References: Photovoltaic Systems, p. 311-320 NEC 690.41, 690.42


Equipment Grounding

An equipment grounding conductor (EGC) connects all exposed non-current-carrying metal parts of PV module frames, support structures, enclosures and raceways to ground [690.43]. Equipment grounding is required for all PV systems operating at any

voltage. Proper bonding between these metal parts is required whenever there is a

transition between different components or equipment.

The EGC can be a conductor, busbar, metallic raceway, or structural component.

EGCs must be installed in the same raceway as the PV circuit conductors upon leaving the vicinity of an array.

Presenter

Presentation Notes

Equipment grounding is required for all PV systems. Equipment grounding and equipment grounding conductors are addressed in NEC Article 250, Part VI. Routing equipment grounding conductors with PV array circuit conductors is required upon leaving the array location, and helps achieve the shortest time constants for the operation of overcurrent devices. References: Photovoltaic Systems, p. 311-319 NEC 690.43, 250 Part VI


Equipment Grounding

PV module frames must be grounded to their support structures using an approved method rated for outdoor use. Splices between separate structural member must be bonded.

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Presentation Notes

Several methods are permitted to provide equipment grounding for PV modules. Traditional methods use self-tapping screws and cup washers, or lay-in lugs attached to the module frames to connect the EGC. Other methods include using bonding washers or clips between module frames and supports, and the EGC is connected to the support structure. EGCs smaller than 6 AWG must be protected from physical damage, and copper grounding conductors should never be allowed to touch aluminum module frames or supports. Refer to PV module and mounting system manufacturer’s installation instructions for specific grounding requirements. References: Photovoltaic Systems, p. 311-319 NEC 690.43, 250 Part VI


Equipment Grounding

Special equipment bonding

washers may be used to provide module frame to support structure connections for equipment grounding.

Unirac

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Presentation Notes

Equipment secured to and electrically connected to metal structures with approved means is considered to be grounded. Devices listed and identified for bonding the exposed metallic frames of PV modules to grounded mounting structures are permitted, but are not approved for all modules and mounting structures. Equipment grounding locations on module frames and required grounding hardware must be identified in the listed installation instructions. References: Photovoltaic Systems, p. 311-319 NEC 690.43, 250 Part VI Wiley Electronics: www.we-llc.com PV module and mounting system installation instructions


Equipment Grounding

Special bonding jumpers, stainless-steel bonding washers and lay-in lugs may be used to electrically connect separate components or attach equipment grounding conductors.

Presenter

Presentation Notes

Equipment secured to and electrically connected to metal structures with approved means is considered to be grounded. Devices listed and identified for bonding the exposed metallic frames of PV modules to grounded mounting structures are permitted, but not approved for all modules and mounting structures. Equipment grounding locations on module frames and required grounding hardware must be identified in listed installation instructions. References: Photovoltaic Systems, p. 311-319 NEC 690.43, 250 Part VI Wiley Electronics: www.we-llc.com PV module and mounting system installation instructions


Equipment Grounding Conductor Size

The minimum size equipment grounding conductors are based on the rating of the overcurrent device ahead of the equipment [690.45, 250.122].

Overcurrent Device Rating

Minimum Size of EGC (Copper, AWG)

15 14

20 12

30 10

40 10

60 10

100 8

200 6

Adapted from NEC Table 250.122

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Presentation Notes

Table 250.122 gives the minimum size equipment grounding conductors for grounding raceways and equipment. For example, a PV source circuit with protected with a 20 A fuse requires a minimum size EGC of 12 AWG. If no overcurrent device is used as permitted by the exception to 690.9, the an assumed overcurrent device rating equal to the short-circuit current for the source circuit is used in Table 250.122. Equipment grounding conductors must not be smaller than 14 AWG or as given in Table 250.122, and are not required to be larger than the circuit conductors. Where a single equipment grounding conductor is routed with multiple circuits in the same raceway or cable, or cable tray, it is sized for the largest overcurrent device protecting any conductors in the raceway or cable. For systems without ground-fault protection, the equipment grounding conductors must be sized for at least twice the temperature and conduit fill derated circuit conductor ampacity. Reference: Photovoltaic Systems, p. 316-317 NEC 690.45, 250.122, Table 250.122


Equipment Grounding Conductor Size

PV array equipment grounding

conductors smaller than 6 AWG must be protected where subjected to physical damage [690.46, 250.120(C)].

Presenter

Presentation Notes

Equipment grounding conductors connecting modules and support structures are generally exposed until they reach a combiner or junction box. In cases where smaller conductors are exposed to possible physical damage during maintenance or other activities, best installation practice suggests using a 6 AWG conductor for the EGC, which is more durable and does not require protection. Reference: NEC 690.46, 250.120(C)


Grounding Electrode System

A grounding electrode system consists of a rod, pipe, plate, metal water pipe, building steel or concrete-encased electrode, and includes all grounding electrodes at a building or structure that must be bonded together.

The grounding electrode conductor (GEC) connects the grounded system conductor or the equipment grounding conductor (EGC) to a grounding electrode system:

Must be a continuous length without splices except for irreversible

connections. A 6 AWG GEC may be secured to and run along building surfaces where

protected from damage. GECs smaller than 6 AWG must be in metal raceways or armored cables.

Presenter

Presentation Notes

References: Photovoltaic Systems, p. 311-313 NEC 250.50, 250.52, 250.53


Rod and Pipe Electrodes

Rod and pipe grounding electrodes must be installed with 8 feet

in contact with the soil, preferably driven vertically to a depth of 8 feet.

Ground clamps installed above ground must be protected from physical

damage, and clamps installed below ground must be listed for direct burial.

Rod, pipe and plate electrodes must be augmented by an additional grounding electrode if the resistance is not 25 ohms or less.

The minimum required spacing between ground rods is 6 feet.

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Presentation Notes

All rod and pipe grounding electrodes must be installed with 8 ft in contact with the soil, preferably driven to a vertical depth of 8 ft. Where rock is encountered, the electrode may be installed at an angle up to 45 degrees, or if that is not possible, buried in a trench 30 inches deep. Burying the ground rod is permitted only if it is not possible to drive the rod vertically or at an angle. Ground clamps used on buried electrodes must be listed for direct earth burial. Reference: NEC 250.53, 250.56


Grounding Electrode System

The grounding electrode system requirements are specified for

the following types of PV systems:

Alternating-current (AC) systems

Direct-current (DC) systems

Systems with AC and DC grounding requirements

Presenter

Presentation Notes

NEC 690.47 establishes specific requirements for the grounding electrode system used for PV installations. The requirements are given for alternating-current (AC) systems, direct-current (DC) systems, and system with both AC and DC grounding requirements. The existing grounding electrode system should be checked as part of any PV installation, particularly for older facilities that may have degraded grounding systems. Verify that all available grounding electrodes at the facility are bonded together, and that the grounding electrode conductors are properly installed and sized. References: Photovoltaic Systems, p. 311-313 NEC 690.47, 250.50, 250.52


Grounding Electrode System: AC Systems

PV systems having only AC system grounding requirements include systems using AC modules or module-level micro inverters. All other types of PV systems have DC circuits.

A grounding electrode system must be provided or installed as

required in 250.50 through 250.60.

The size of the GEC is based on the largest ungrounded system conductor as listed in Table 250.66.

Must be at least 8 AWG copper, or no larger than 6 AWG copper if

connected to a pipe or plate electrode.

Presenter

Presentation Notes

References: Photovoltaic Systems, p. 311-313 NEC 690.47(A), 250.50-250.60, 250.64, Table 250.66


Grounding Electrode System: DC Systems

PV systems having only DC grounding requirements including

stand-alone systems with only DC loads and DC circuits.

The size of the DC GEC may not be smaller than the largest conductor supplied by the system, and not smaller than 8 AWG copper.

Where connected to rod, pipe, or plate electrodes the GEC is not

required to be larger than 6 AWG copper.

Presenter

Presentation Notes

References: Photovoltaic Systems, p. 311-313 NEC 690.47(B), 250.166, 250.169, Table 250.166


Grounding Electrode System: AC and DC Systems

PV systems with no direct connection between the DC and AC

grounded circuit conductors require a DC grounding system.

This applies to most interactive PV systems, except those systems using AC modules.

Three grounding options are allowed for systems with AC and DC grounding requirements:

1. A separate DC electrode is used and bonded to the AC grounding

electrode. 2. A common grounding electrode is used for the AC and DC circuits. 3. The DC grounding electrode conductor (GEC) is combined with the AC

equipment grounding conductor (EGC).

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For most utility-interactive systems, the grounded DC conductor, the DC equipment grounding conductor, and the AC equipment grounding conductor are terminated in the inverter. The EGC is connected to the DC grounded circuit conductor through the GFID circuit. The premises grounding system serves as the AC grounding system, and the DC GEC is combined with the AC EGC. Reference: NEC 690.47(C)


Grounding Electrode System: AC and DC Systems – Option 1

When a separate DC electrode is used, it must be bonded to the

AC grounding electrode.

Bonding jumpers must be sized based on the larger of the DC GEC and AC GEC size.

The DC GEC or bonding jumpers may not substitute for any required AC equipment grounding conductors.

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Reference: NEC 690.47(C)(1)



A common grounding electrode may be used for the AC and DC

system grounding requirements, and requires the following: The DC GEC must run from a marked DC GEC connecting point to the

AC grounding electrode, or the AC GEC if the AC grounding electrode is unavailable.

The DC GEC may not substitute for any required AC equipment grounding conductors.

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The marked DC GEC connection point is usually inside the inverter. The common grounding electrode is usually the AC service grounding electrode system. Reference: NEC 690.47(C)(2), 250.166, 250.64(C)(1)



The DC grounding electrode conductor (GEC) may be combined

with the AC equipment grounding conductor (EGC). This grounding conductor must: Run continually without splices (irreversible splices permitted),

Be connected to the DC GEC at a marked termination point, and

Be sized for the larger of the size of the equipment grounding conductors

(EGCs) and the size of the DC grounding electrode conductor (GEC).

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The marked DC GEC connection point is usually inside the inverter. The common grounding electrode is usually the AC service grounding electrode system. Reference: NEC 690.47(C)(3), 250.122, 250.166, 250.64(E)


Continuity of Grounding and Grounded Conductors

The continuity of the EGC and grounded conductors from PV

source circuits and output circuits must be maintained whenever equipment is removed for service or maintenance.

Temporary equipment bonding jumpers may be required if either grounding system is disconnected during maintenance.

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Reference: Photovoltaic Systems, p. 317 NEC 690.48, 690.49, 250.120(C)


Additional Grounding Electrodes

Additional grounding electrodes at the PV array location were

required in the 690.47(D) of the 2008 NEC, but removed from the 2011 NEC.

If the GEC from a roof-mounted array is dropped vertically and falls within 6 feet of an existing grounding electrode, an additional array grounding electrode is not required.

Where required, the DC grounding electrode conductor usually needs to be a minimum size 6 AWG copper.

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References: 2008 NEC 690.47(D) Photovoltaic Systems, p. 313


Lightning Protection Systems

The lightning protection systems on buildings must be bonded to

the electrical service grounding electrode system.

Conductive metal parts of PV electrical systems including support structures, raceways, combiner boxes or other metal equipment may require certain spacing from or bonding to the lightning protection system.

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Conductive metal parts of PV electrical systems including support structures, raceways, combiner boxes or other metal equipment installed in the vicinity may require certain spacing from or bonding to the lightning protection system. References: Photovoltaic Systems, p. 318-319 NEC 250.106 NFPA 780 UL 96A


Summary

Article 690 and numerous other sections of the National Electrical Code establish the installation requirements for PV systems.

The size and ratings for conductors and overcurrent protection devices are determined from the maximum circuit voltages and currents associated with the connected equipment.

Disconnect means isolate major equipment and circuits for safety and maintenance.

Grounding and bonding reference equipment and circuits to earth

potential to protect equipment from surges and reduce the hazard for electrical shock.

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Questions and Discussion

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Documents

Chapter 11 · Calculating circuit voltages and currents based ... to other electrical systems are covered in Chapter 12 ... PV array DC power generating