National Electrical Code® (NEC®)

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Professional Studies ProgramProf. Jaime Jose Laracuente-Diaz

NEC®

• 1879– Thomas Alva Edison - First practical incandescent light bulb– National Association of Fire Engineers met to discuss standards

for electrical installation.

• 1895 – There were five separate codes in the USA.

• 1896– A meeting was held between various organizations to define a

code.

• 1897– The National Electrical Code was adopted and is often referred

as the Code.

NEC®

• National Fire Protection Association (NFPA) is now the sponsor association for the Code.

• It is officially endorsed by the American National Standards Institute (ANSI).

• The NFPA Electrical Code Committee NEC® is named as the ANSI Standards Committee C1.

NEC®

• Purpose:

– “practical safeguarding of persons and property from hazards arising from the use of electricity”

• It is meant as a legal document which could be interpreted by governmental bodies and agencies with jurisdiction on this matter (electrical installations).

NEC®

• The Code generally applies to the installation of electrical conductors and equipment within private and public facilities up to the connection point to the power source.

NEC®

• NEC Areas:– Introduction – (1) General – (2) Wiring and Protection– (3) Wiring Methods and Materials– (4) Equipment for General Use– (5) Special Occupancies– (6) Special Equipment

NEC®

• (7) Special Conditions• (8) Communication Systems• (9) Tables• Annex A: Product Safety Standards• Annex B: Information for Ampacity

Calculation • Annex C: Conduit and Tubing Fill table• Annex D: Examples

NEC®

• Annex E: Types of Construction

• Annex F: Cross Reference Tables

• Annex G: Administration and Enforcement

NEC® Coverage Diagram

Generation Area Substation Area Coverage Area

Figure concept taken from Reference [1].

NEC® Coverage

• It is important to mention that the NEC is the most used standard in the USA and it is basically complemented with local codes and regulations in different states, cities or counties.

• Other regulations applies to the generations and distribution process of electrical power.

NEC®

• Introduction (Article 90)

• Permissive rule – One allowed but not required (an alternative)– These alternatives are highlighted using the

term “shall be permitted”.

NEC® - General Portion

• General Portion – (Articles 100): Definitions– (Articles 110): Requirements for electrical

installation.

NEC® - General Portion

Power supply source

Panel board

Power Panelboard

sub-feedermain-feeder

feeder

branch ckts

branch ckts

Panel Board

Fixed OvercurrentProtective

device

NEC® - General Portion

• Overcurrent– Any current in excess of rated current.

• The selection of proper conductor size is extremely important to avoid this situation.– AWG = American Wire Gage

NEC® - General Portion

• Example:– We have a wire of unknown gage but the give

diameter is 0.2591 [cm]• Convert the diameter from [cm] to [inches].• Use the AWG table to identify the AWG number

given the wire diameter in inches.

NEC® - Wiring and Protection

• Wiring and Protection– (Article 200): Grounded Conductors– (Article 210): Branch Circuits– (Article 215): Feeders– (Article 220): Branch Circuit, feeder and

service calculations– (Article 225): Outside Branch Circuits and

Feeders– (Article 230): Services

NEC® - Wiring and Protection

– (Article 240): Over-current Protection– (Article 250): Grounding– (Article 280): Surge Arresters– (Article 285): Transient Voltage surge

suppressors

NEC® - Wiring and ProtectionGrounded Conductors

• Grounded Conductor– It is intentionally grounded.– For example: the neutral wire of an electrical

system– It is identified by a white o natural gray outer

finish or by three continuous white stripes on other than green insulation (See Article 200.6).

NEC® - Wiring and ProtectionGrounded Conductors

• Grounding Conductor– It is used to connect equipment or the

grounded circuit (neutral) of a wiring system to a grounding electrode and which is colored green (See Articles 100 and 250.119).

NEC® - Wiring and ProtectionBranch Circuits

• How do I calculate the number of branch circuits required in a building?– The section 210.11 of the Code is used for

this purpose. – For example:

• A dwelling unit is required to have two or more 20-A small appliance branch circuits beyond that calculated, one 20-A branch circuit for laundry and one 20-A branch circuit for each bathroom. (Section 210.11 C)

NEC® - Wiring and ProtectionBranch Circuits

• Ground Fault Circuit Interrupter

Trip.GFCI

Utilization equipment

Current travelers

BranchCircuitPower supply

NEC® - Wiring and ProtectionBranch Circuits

• Ground Fault Circuit Interrupter– Are required to be installed outdoors and in

dwelling units bathrooms, garages, crawl spaces, unfinished basements, kitchens, wet bar sinks, and boat houses. (See Section 210.8 (A)).