Pres18 - Testing and Maintenance 2-02

© 2001 Cooper Bussmann, Inc.

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Testing & Maintenance

Testing & Maintenance


CB Testing & Maintenance – General Considerations

• Circuit breakers require– Testing and maintenance

• Verify proper calibration and operation

• Testing performed with the circuit breaker removed from the enclosure

• Required for all circuit breakers and may require special equipment

– Operation at least once per year

• Testing and maintenance are required to ensure proper protection by circuit breaker systems.

• Molded case and insulated case circuit breakers cannot be repaired – must replace if testing shows CB is out of calibration or inoperative.


CB Replacement Required After High Fault Current Interruption

• IEEE Std 1015-1997 (Blue Book) - Recommended Practice for Applying Low-Voltage Circuit Breakers Used in Industrial and Commercial Power Systems– 3.35 Circuit Breaker Useful Life

– It is prudent to replace any MCCB that has interrupted, at most, two faults at rated maximum current.

• UL 489– MCCBs are tested, per UL 489, to clear a fault at their three

phase interrupting rating twice. First with closing the circuit on the circuit breaker (O), then a period of rest of 2-60 min (t), then closing the circuit breaker on the circuit (CO).


CB Maintenance & Testing – Frequency

• IEEE Std 902-1998 (Yellow Book) - Guide for Maintenance, Operation and Safety of Industrial and Commercial Power Systems

– Maintenance/Test Frequency• 5.5 Inspection and Test Frequency

– Manufacturers’ service manuals should be consulted in determining an adequate frequency.

– A good guide for both maintenance and testing frequency is found in NFPA 70B.

• NFPA 70B (1998) - Recommended Practice for Electrical Equipment Maintenance18-4 Frequency of Tests:– The optimum cycle depends on the use to which the equipment is

put and the operating and environmental conditions of the equipment. In general, this cycle can range from six months to three years, depending upon the above criteria.


MCCB Power Panel Maintenance and Testing

• NFPA 70B: 11-2 Application Considerations– Circuit Breaker nuisance tripping can result from:

• High ambient temperature

• Poor or improper connections

• Damaged plug-in connections

• Other conditions that transfer heat to the breaker mechanism

• Continuous current (for three hours or more) in excess of 80% of the breaker continuous current rating.



• NFPA 70B: 11-7 Types of Maintenance– Mechanical

• Good Housekeeping

• Proper mechanical mounting

• Proper electrical connections

• Manual Operation

– Electrical• Field testing conditions as outlined in 18-10.2.4



• NFPA 70B: 11-8 Inspection and Cleaning– Circuit breakers should be kept clean of external

contamination to ensure:• Proper heat dissipation

• Reduced potential arcing conditions between live conductor and between live conductors and ground.

– Circuit breaker case should be inspected for cracks and replaced if necessary.• Cracks could reduce structural strength needed to withstand

stresses encountered during fault-current interruptions.



• NFPA 70B: 11-9 Loose Connection– Loose connections represent the most common cause

of excessive heat and can cause nuisance tripping of circuit breakers and possibly an eventual failure.• Periodic maintenance checks should involve checking for

loose connections or evidence of overheating.

• Loose connections should be tightened as required using manufacturer’s recommended torque values.

• Circuit breakers with field installed interchangeable trip units could overheat if not properly tightened during installation.



• NFPA 70B: 11-11 Mechanical Mechanism Exercise– Since circuit breakers may be in service for extended

periods where overload or short-circuit tripping operation is not required, manual operation is needed.• Manual operation of the circuit breaker will help keep the

contacts clean and exercise the breaker mechanism.

• Manual operation does not exercise the tripping mechanism or mechanical linkages in the tripping mechanism. Push-to-trip buttons (if equipped) should be operated in order to exercise the tripping mechanism and linkages.


Circuit Breaker Testing

• NFPA 70B: 18-10.2.4 Molded-Case Circuit Breaker Testing

(a) Molded Case Circuit Breakers – General

– Electrical testing of circuit breakers should be performed in a manner and with the type of equipment required by the type of trip unit employed.

– Trip unit types can be:» Factory sealed, non-interchangeable trip» Interchangeable trip» Solid state trip




(b) Testing Thermal-Magnetic Circuit Breakers.

– The electrical testing of thermal-magnetic circuit breakers can be divided into three steps:

1) Overload of individual poles at 300% of trip rating

2) Verification of test procedures

3) Verification of manufacturer’s published data

– Consult NEMA AB2 – Procedures for Verifying Field Inspection and Performance Verification of Molded-Case Circuit Breakers as well as manufacturer’s recommended testing procedures.




• (c) Overload Testing Considerations

– Overload tests on individual poles at 300% rated current– The reaction of the circuit breaker to this overload is

indicative of its reaction throughout its entire overcurrent tripping range.

• (d) Overcurrent Trip Data (at 300%)

– Table 18-10.2.4(d) outlines the current and trip-time values as recommended by NEMA.

– Table values are indicative for most manufacturers, for more specific values, refer to the manufacturer’s data for the circuit breaker being tested.



• NFPA 70B: 18-10.2.4 Molded-Case Circuit Breaker Testing• (e) Evaluation of Results

– Minimum Trip Times

» Table values are not considered significant unless nuisance tripping has been experienced.

» Table values are provided as a guideline only.

» If minimum tripping times are lower, the breaker should be retested.

– Maximum Trip Times

» Under normal test conditions, the breaker will trip in less than the maximum table values.

» Under improper test conditions, the breaker can exceed the maximum table values.




• (e) Evaluation of Results

– Maximum Tripping Times for Cable Protection» If the test value exceeds the maximum tripping

times from the table, but does not exceed the maximum tripping times for cable protection from the table, the circuit breaker is providing an acceptable level of protection.

» Coordination with other protective devices should be considered before replacing a circuit breaker that trips beyond the time-current curve.




• (f) Testing Instantaneous-Only Circuit Breakers.

– The testing of instantaneous only circuit breakers requires the use of elaborate constant rate-of-rise test equipment coupled with accurate current-monitoring instrumentation - preferably digital readout - for accurate confirmation of manufacturers’ test results.


CB Maintenance & Testing

• Is the testing and maintenance required per NFPA 70B sufficient?

• Are other sources available for recommended testing and maintenance of circuit breakers?– NEMA AB4 (1996) - Guidelines for Inspection and

Preventive Maintenance of Molded Case Circuit Breakers Used in Commercial and Industrial Applications.



• NEMA AB 4 - Recommended Tests• Mechanical Operation

• Insulation Resistance Test

• Individual Pole Resistance Test

• Inverse Time Overcurrent Trip Test

• Instantaneous Overcurrent Trip Test

• Rated Hold-In Test



• NEMA AB 4 – Recommended Tests– Mechanical Operation (Section 5)

• Breaker Handle should operate smoothly without binding

• Verify that all circuit breaker contacts are open when the handle is in the off position and closed when in the on position

• Verify operation of the mechanical trip provisions (push-to-trip button) if available and verify if contacts are opening and closing.

• Replace circuit breaker if

– The contacts are not open in the “off” or “tripped” position

– The push-to-trip button (if provided) does not trip breaker.

– The contacts are not closed in the “on” position

– The breaker does not reset



• NEMA AB 4 – Recommended Tests– Insulation Resistance Test (Section 5)

• Determines resistance of breaker by applying a direct current voltage of at least 500 volts.

• Between line & load terminals (breaker off)

• Terminals of adjacent poles (breaker on)

• Line terminals to metal baseplate (breaker on).

• Results should be one mega ohm or greater.

• Any reading less than one mega ohm may indicate contaminated, flawed, or cracked insulating material.



• NEMA AB 4 – Recommended Tests– Individual Pole Resistance Test (Section 5)

• Tests each pole with test current equal to breaker rating and measure voltage drop and consult the manufacturer for acceptable values.

• If test values exceed manufacturer’s data, a potential overheating condition may be indicated and additional tests may be required, consult the manufacturer for more guidance.



• NEMA AB 4 – Recommended Tests– Inverse Time Overcurrent Trip Test (Section 5)

• Test each pole separately at 300% of rated current

• Test with minimum of 4 feet rated copper conductor as listed in Table 5-1 or copper busbar connections for circuit breakers over 1600A, as listed in Table 5-2.

• Verify results with Table 5-3 which gives maximum trip time based upon breaker rated current (or consult manufacturer). Varies from Table Table 18-10.2.4(d) in NFPA 70B.



• NEMA AB 4 - Recommended Tests– Instantaneous Overcurrent Trip Test (Section 5)

• Use Run-up or Pulse Method (Pulse Method more accurate)

• Pulse Method:

– Apply pulse of current for 5-10 cycles approximately 10 percent below lower tolerance trip level. Breaker should not trip.

– Apply pulse of current for 5-10 cycles equivalent to the high tolerance trip level. Breaker should trip.

– Tolerance trip level 25% for non-adjustable, -30% to +40% for adjustable trip.



• NEMA AB 4 – Recommended Tests– Rated Hold-In Test (Section 5)

• Test all three poles in series with copper conductors not less than 4 feet in length.

• Deliver rated current until the circuit breaker temperature stabilizes.

• Typical stabilization - 1 hour 100A or less, several hours for breakers larger than 100A


Switchgear Assembly Testing and Maintenance

• NFPA 70B: 6-2.2 Frequency of Maintenance– Frequency of maintenance depends upon environmental and

operating conditions, no fixed rule can govern all applications.

– Follow specific manufacturers’ recommendations regarding inspection and maintenance.

– Inspection of switchgear focuses on:

• The enclosure integrity and security

• Moisture, condensation and ventilation

• Insulation and Insulator integrity

• Signs of corona, tracking and thermal damage.


Air Circuit Breaker Testing and Maintenance• NFPA 70B: 6-4 Air Circuit Breakers

– 6-4.1 General• Consult manufacturers instruction manuals before

performing maintenance work.

• Open and remove Drawout-type breaker for maintenance.

• De-energize all sources of power for fixed- or bolted-type circuit breakers.

– 6-4.2 Insulation• Remove and clean interphase barriers.

• Inspect for signs of corona, tracking, or thermal damage.


Air Circuit Breaker Testing and Maintenance

• NFPA 70B: 6-4 Air Circuit Breakers– 6-4.3 Contacts

• Inspect main and arcing contacts to assure:

– Contacts are clean, smooth and in good alignment– Contact pressure is normal as prescribed in the

manufacturers’ literature.

– 6-4.4 Arc Interrupters• Inspect and clean arc interrupters

• Check for broken or cracked ceramic parts, erosion of ceramic parts and dirt in interrupters.



• NFPA 70B: 6-4 Air Circuit Breakers– 6-4.5 Operating Mechanism

• Inspect for loose or broken parts, missing cotter pins or retaining keepers, missing nuts or bolts, and binding or excess wear.

• Check closing and tripping action for quick, positive and smooth operation.

– 6-4.6 Breaker Auxiliary Devices• Inspect auxiliary devices (closing motor, shunt trip,

auxiliary switches, and bell alarm switch) for correct operation and condition.



• NFPA 70B: 6-4 Air Circuit Breakers– 6-4.5 Operating Mechanism

• Inspect for loose or broken parts, missing cotter pins or retaining keepers, missing nuts or bolts, and binding or excess wear.

• Check closing and tripping action for quick, positive and smooth operation.

– 6-4.6 Breaker Auxiliary Devices• Inspect auxiliary devices (closing motor, shunt trip,

auxiliary switches, and bell alarm switch) for correct operation and condition.

• Inspect protective relays and trip units for correct operation.


Air Circuit Breaker Testing and Maintenance• NFPA 70B: 18-10.2.5 Low-Voltage Power Circuit Breakers

(a) Overcurrent Trip Device

• Can be electromechanical or solid state with two or more of the following types of elements.

– Long Time-Delay Element

» Operates on overloads between its pickup setting and the pickup of a short time delay or an instantaneous element.

» Pickup setting is typically 80% to 160% of the trip device rating (rating does can not exceed breaker frame size rating).

– Short Time-Delay Element

» Has time delay measured in cycles and is used to delay tripping, for coordination purposes, to allow downstream molded case circuit breakers to trip first.

» Pickup settings is typically 250% to 1000% of the trip device rating.


Air Circuit Breaker Testing and Maintenance• NFPA 70B: 18-10.2.5 Low-Voltage Power Circuit

Breakers

(a) Overcurrent Trip Device (Continued)

– Instantaneous Element» Has no intentional time delay and is used to protect

against heavy fault currents and short circuits.» Pickup settings typically range from 500% to 1500%.

– Ground-Fault Element» Available only on solid-state devices and is used to

protect against ground-fault currents at levels below those that would be sensed otherwise.



• NFPA 70B: 18-10.2.5 Low-Voltage Power Circuit Breakers(b) Testing

• Primary injection method is used to test both electromechanical and solid-state devices.

• Testing requires use of high-current test set capable of producing sufficient current at low voltage to operate each of the trip element devices.

• Testing should include at least one test in the range of each element of the trip device.

– Long time-delay should be tested at 300% of its setting.– Short time-delay should be tested at 150-200% of its

setting.– Instantaneous should be tested at 90-110% of its

setting.


Fuse Maintenance & Testing• NFPA 70B: 13-1 Fuses Rated 1000 Volts

or Less– 13-1.1 Installing and Removing

• De-energize before installing or removing fuses.

• If impossible to de-energize, take appropriate safety precautions (See NFPA 70E).

– 13-1.2 Inspection• Fuse terminals and fuse clips should be examined

for discoloration caused from heat or corrosion.

• Use of infrared examination can provide early detection of overheating.

• Determine cause of overheating if present.


Fuse Maintenance & Testing

• NFPA 70B: 13-1 Fuses Rated 1000 Volts or Less– 13-1.3 Cleaning and Servicing

• Fuseholder connections should be tightened.

• Check to insure proper clip pressure.

• Clean contact surfaces of fuse terminals and clips that have become corroded or oxidized.

• Wipe contact surfaces with noncorrosive cleaning agent.

• If signs of deterioration, such as discolored or damaged casings or loose terminals, replace.


Fuse Maintenance & Testing

• NFPA 70B: 13-1 Fuses Rated 1000 Volts or Less– 13-1.4 Replacement

• Assure replacement fuses are of the proper type and rating.

• When replacing fuses, never alter or force fuseholders to accept fuses that do not readily fit.

• An adequate supply of spare fuses with proper ratings will minimize replacement problems.


Fuse Testing & Maintenance

• NFPA 70B: 18-10 Protective Device Testing• 18-10.1 Fuses

– Test with a continuity Tester to verify the fuse is not open

– Resistance readings can be taken and should be compared against values recommended by the manufacturer

– Where manufacturers’ data is not readily available, resistance deviations of more than 50% for identical fuses should be investigated.


Fusible Disconnect Switch Testing and Maintenance

• Disconnect Switches in Panelboards– NEMA PB 1.1 (1996) – General Instructions for

Proper Installation, Operation, and Maintenance of Panelboards rated 600 Volts or less

• Bolted Pressure Switches in Switchboards– Refer to manufacturers’ instructions

– Refer to PB 2.1 (1996) – General Instructions for Proper Handling, Installation, Operation, and Maintenance of Deadfront Distribution Switchboards Rated 600 Volts or Less.

• Similar requirements as PB 1.1


Fusible Disconnect Testing and Maintenance

• NEMA PB 1.1 - Section 8 – Maintenance– 8.2 – Remove all power to panelboard and check for signs of

overheating.

– 8.3 - Inspect the panelboard once per year or after any severe short circuit.• Look for any moisture or signs of previous wetness or dripping inside

enclosure and conduit entering enclosure.

• Remove any dust and dirt from panelboard.

• Examine electrical connections in the bus, terminals and wiring system for tightness and signs of overheating.

• Examine fuse clip contact pressure and contact means for signs of overheating or looseness, check spring pressure and tightness of fastening means. Replace as needed.

• Check the operation of all mechanical components.

• Examine all devices and bus supports for cracks or breakage and replace components as required.


Fusible Disconnect Testing and Maintenance

• NEMA PB 1.1 - Section 8 – Maintenance– 8.4 – Clean and dress readily accessible copper electrical contacts,

blades, and jaws according to manufacturers’ instructions.

– 8.5 – Lubricate switches and operating mechanisms according to the manufacturers’ instructions which are usually printed on diagrams or labels.• Operate each switch or circuit breaker several times to assure

mechanisms are free and in proper working order. Replace as needed.

• Check circuit breaker and fuses to ensure proper ampere, voltage, and interrupting ratings. Ensure non-current-limiting devices are not used as replacements for current-limiting devices. Do not attempt to defeat rejection mechanisms which are provided to prevent the installation of incorrect fuse classes.

• Check insulation resistance after short-circuit, replacement or cleaning of parts or if exposed to high humidity, condensation, or dripping moisture.


Ground-Fault Protection Testing and Maintenance

• NFPA 70B: 12-2 Ground-Fault Circuit Interrupters (GFCIs)– 12-2.2 Maintenance

• Test button on the unit should be used for tripping tests in accordance with the frequency recommended by the manufacturer.

• Use of separate listed test instruments are available and recommended for testing and troubleshooting of GFCIs.

• When using separate GFCI test instrument which indicates “No Trip”, but the GFCI integral test button indicates “Trip”, investigate the circuit for mis-wiring such as:

– Line and load wires transposed, Reverse polarity, Open ground• If GFCI is properly wired but fails test, the test result is indicative of an

improperly functioning GFCI.


Ground-Fault Protection Testing and Maintenance

• NFPA 70B: 12-3 Ground-Fault Protectors (GFPs)– 12-3.5 Maintenance

• Inspect sensors for tight terminal connections and cleanliness

• Interconnections between components should be marked and replaced to maintain proper phasing and circuitry if disconnected.

• If equipped with a test panel, a formal program of periodic testing should be established.

• If not equipped with a test panel, the manufacturer should be consulted for test instructions.

• Repairs should be performed by the manufacturer.

Documents

Pres18 - Testing and Maintenance 2-02