NEC Electrical Engineering cheat sheet

NEC Article 90 covers purpose and scope; Article 100 defines terms; Chapters 1-4 apply generally, Chapters 5-7 supplement or modify, Chapter 8 (communications) is independent, and Chapter 9 contains tables.

Article 110 covers general requirements for electrical installations: 110.26 working clearances, 110.14 terminations, and 110.3 listing and labeling.

110.26(A) working space depth is 3 ft for 0-150 V to ground, 3.5 ft for 151-300 V, 4 ft for 301-600 V, and 5 ft for over 600 V, measured from the live parts or enclosure front.

110.26(A)(2) width of working space is the width of the equipment or 30 in, whichever is greater, and must allow the equipment doors to open at least 90 degrees.

110.26(E) dedicated equipment space extends from the floor to 6 ft above the equipment or to structural ceiling, whichever is higher, and is reserved for the equipment served.

110.14(C) ampacity of conductors must be selected and coordinated so the lowest temperature-rated conductor, termination, or device is not exceeded.

Conductor ampacity adjustment factors (310.15) apply to current-carrying conductors; neutral counts as current-carrying only when it carries nonlinear harmonic current or is part of a 3-wire circuit with line-to-neutral loads.

Informational Notes in the NEC are explanatory only and are not enforceable as code requirements; only the mandatory text and referenced standards govern.

Chapter 3 wiring methods each have an Article: 320 armored cable, 330 metal-clad cable, 334 nonmetallic-sheathed cable, 338 service-entrance cable, 348 flexible metal conduit, 350 liquidtight flexible metal conduit, 352 PVC conduit, 358 EMT.

300.5 minimum cover for direct-buried conductors: 24 in for general use, 18 in for residential branch circuits at 120 V or less with GFCI, 12 in for 120 V landscape lighting, and 6 in for rigid metal conduit under a 4-in concrete slab.

300.5(D) requires a warning ribbon 12 in above buried service conductors and protection from physical damage where conductors emerge from grade.

334.30 NM cable must be secured within 12 in of boxes and supported at intervals not exceeding 4.5 ft; 334.17 requires protection where cable passes through framing members near the edge.

348.30 FMC must be secured within 12 in of boxes and supported at intervals not exceeding 4.5 ft; 348.60 requires an equipment grounding conductor where flexibility is needed or the raceway is over 6 ft.

352.30 PVC conduit support intervals: 3 ft for trade sizes 1/2 through 1, 5 ft for 1-1/4 through 2, and 10 ft for 2-1/2 and larger, with expansion fittings where thermal movement occurs.

358.30 EMT must be securely fastened within 3 ft of boxes and supported at intervals not exceeding 10 ft; 358.24 requires reaming of cut ends.

310.16 ampacity tables are based on 30 degrees C ambient; 310.15(B)(2)(a) correction factors apply for ambient temperatures above 30 degrees C.

210.52(A) dwelling receptacle spacing: no point along the floor line of a wall space is more than 6 ft from a receptacle outlet, and wall spaces 2 ft or wider require a receptacle.

210.52(C) countertop receptacles: no point on the countertop is more than 24 in from a receptacle, and at least one receptacle is required for each island or peninsula.

210.8 GFCI protection is required in dwelling bathrooms, garages, outdoors, kitchens, laundry areas, and within 6 ft of sinks; 210.12 AFCI protection covers dwelling branch circuits in most habitable rooms.

210.11(C)(3) requires at least one 20 A laundry branch circuit in dwellings; 210.11(C)(1) requires at least two 20 A small-appliance branch circuits in kitchens.

220.82 optional feeder/service calculation for dwellings: 100 percent of first 10 kVA plus 40 percent of the remainder of general load, plus nameplate ratings of appliances and motors.

220.12 general lighting load is 3 VA per square foot for dwellings and 1 VA per square foot for hospitals; 220.42 applies lighting demand factors.

220.54 electric clothes dryers are calculated at 5000 VA or nameplate, whichever is larger, with demand factors in Table 220.54 for multiple dryers.

210.19(A) branch-circuit conductors must have ampacity not less than the noncontinuous load plus 125 percent of the continuous load; 210.20 applies the same rule to overcurrent devices.

250.52 grounding electrode system includes metal underground water pipe (in contact with earth 10 ft or more), metal building frame, concrete-encased electrode, ground ring, rod/pipe electrodes, and plate electrodes.

250.66 sizes the grounding electrode conductor based on the largest service-entrance conductor; 250.122 sizes the equipment grounding conductor based on the overcurrent device rating.

250.53(A)(2) requires a supplemental electrode where a single rod, pipe, or plate electrode has a resistance to ground over 25 ohms; 250.53(A)(3) requires 6 ft minimum spacing between electrodes.

250.24(A)(5) prohibits using the grounded conductor for grounding on the load side of the service disconnect; 250.32 covers separate buildings and structures.

250.30 covers separately derived systems; the system bonding jumper connects the grounded conductor to the equipment grounding conductor at the source.

250.118 lists acceptable equipment grounding conductors, including copper conductors, rigid metal conduit, IMC, EMT, and listed liquidtight flexible metal conduit with internal grounding conductor.

250.148 requires continuity of the equipment grounding conductor at boxes and fittings; 250.134 requires bonding of metal raceways and enclosures.

250.102(C) sizes supply-side bonding jumpers based on the largest ungrounded supply conductor, using Table 250.102(C)(1).

240.4 general rule: conductors must be protected against overcurrent in accordance with their ampacities; 240.4(D) applies the small-conductor limits (14 AWG at 15 A, 12 AWG at 20 A, 10 AWG at 30 A for copper).

240.4(B) permits the next higher standard overcurrent device rating where the conductor ampacity does not correspond to a standard rating, subject to limits for 800 A and below.

240.6(A) standard ampere ratings include 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200 A.

240.21 lists tap conductor rules: 10 ft rule, 25 ft rule, and transformer secondary rules, each with specific ampacity and physical protection conditions.

430.52 motor branch-circuit short-circuit and ground-fault protection: inverse-time breaker at 250 percent of FLC, dual-element fuse at 175 percent, non-time-delay fuse at 300 percent.

240.86 series-rated systems require the combination of overcurrent devices to be listed and marked for the application; the sum of the ratings must not exceed the rating of the load-side device.

240.4(E) applies specific overcurrent protection rules for taps, transformer secondaries, and motor circuits that may permit conductor ampacity below the device rating.

110.9 interrupting rating: equipment must have an interrupting rating not less than the available fault current at its terminals.

430.6(A)(1) motor branch-circuit conductors must be sized at not less than 125 percent of the motor full-load current from Tables 430.248-430.250, not the nameplate current.

430.22 branch-circuit conductors must have ampacity of at least 125 percent of the motor full-load current; 430.24 feeder conductors use 125 percent of the largest motor plus 100 percent of the others.

430.32 overload protection: for motors over 1 hp, 115-125 percent of nameplate current for a marked service factor of 1.15 or higher, 115 percent for a marked temperature rise of 40 degrees C or less.

430.52 short-circuit protection may be increased to the next standard rating if the calculated value does not correspond to a standard size, but not above the maximum limits in Table 430.52.

430.102 requires a disconnecting means within sight of the motor and driven machinery; 430.103 requires the disconnect to open all ungrounded conductors.

440.32 and 440.33 cover hermetic refrigerant motor-compressor branch-circuit conductors and short-circuit protection; 440.6 requires nameplate rated-load current for sizing.

440.52 requires a disconnecting means for air-conditioning equipment within sight of and accessible from the equipment; 440.63 covers the disconnecting means for hermetic compressors.

430.72(B) covers overload protection for conductors; 430.28 applies tap conductor rules for motor branch circuits and feeders.

Article 500 classifies hazardous locations by Class I (gases and vapors), Class II (dusts), and Class III (fibers and flyings); Division 1 is normal conditions, Division 2 is abnormal conditions.

Article 505 uses Zones 0, 1, 2 for gases and Zones 20, 21, 22 for dusts; Zone 0 is continuous presence of flammable gas, Zone 1 is likely during normal operation.

Article 511 covers commercial garages and requires Class I, Division 2 classification for areas up to 18 in above the floor and within defined boundaries.

Article 514 covers motor fuel dispensing facilities, requiring Class I, Division 1 or 2 classification based on the area around dispensers and tanks.

Article 517 covers health care facilities; 517.18 requires hospital-grade receptacles and 517.19 covers critical branch circuits in patient care areas.

Article 680 covers swimming pools, fountains, and similar installations; 680.26 requires equipotential bonding of pool shells, decks, and metal parts.

Article 690 covers solar photovoltaic systems; 690.8 requires conductor ampacity of 125 percent of the maximum current, and 690.12 covers rapid shutdown requirements.

Article 695 covers fire pumps; 695.4 requires a reliable power source and 695.6 covers the dedicated fire pump feeder with specific overcurrent protection limits.

Article 700 covers emergency systems, Article 701 legally required standby systems, Article 702 optional standby systems, and Article 708 critical operations power systems.

700.12 requires an emergency source of power capable of supplying the emergency loads; 700.17 requires separation of emergency circuits from other circuits.

700.16 requires emergency illumination for at least 90 minutes; 700.23 covers the transfer of emergency loads to the alternate source.

Article 760 covers fire alarm systems; 760.41 and 760.43 cover non-power-limited and power-limited fire alarm circuits.

Article 725 covers Class 1, Class 2, and Class 3 remote-control, signaling, and power-limited circuits; Class 2 and 3 circuits are limited in power and voltage.

Article 680.25 requires an insulated equipment grounding conductor in feeders to pool equipment; 680.23 requires GFCI protection for underwater luminaires.

Article 547 covers agricultural buildings; 547.5 requires equipotential planes and 547.9 covers the equipotential bonding grid for livestock.

Article 500.8 requires equipment marking for the class, division, and group; Class I groups are A, B, C, D and Class II groups are E, F, G.

NFPA 70E covers electrical safety in the workplace; Article 130 covers work practices, including energized work permits and approach boundaries.

NFPA 70E arc flash PPE categories or incident energy analysis determine the required arc-rated clothing and equipment for energized work.

The limited approach boundary for 120-750 V is 10 ft for exposed movable conductors and 3 ft 6 in for fixed circuit parts; the restricted boundary is 1 ft for 120-750 V.

OSHA 29 CFR 1910 Subpart S adopts electrical safety requirements for general industry; 1910.333 covers selection and use of work practices.

Lockout/tagout under 1910.147 requires de-energization, verification of de-energization, and application of locks and tags before work.

The NEC is enforced by the authority having jurisdiction (AHJ) under 90.4; the AHJ interprets the code and grants approvals.

Inspection of electrical installations includes verifying grounding and bonding, overcurrent protection, working clearances, and listing of equipment under 110.3.

Test instruments for verification include low-resistance ohmmeters for grounding and insulation resistance testers; test results must be documented for compliance.

NEC Article 90 covers purpose and scope; Article 100 defines terms; Chapters 1-4 apply generally, Chapters 5-7 supplement or modify, Chapter 8 (communications) is independent, and Chapter 9 contains tables.

Article 110 covers general requirements for electrical installations: 110.26 working clearances, 110.14 terminations, and 110.3 listing and labeling.

110.26(A) working space depth is 3 ft for 0-150 V to ground, 3.5 ft for 151-300 V, 4 ft for 301-600 V, and 5 ft for over 600 V, measured from the live parts or enclosure front.

110.26(A)(2) width of working space is the width of the equipment or 30 in, whichever is greater, and must allow the equipment doors to open at least 90 degrees.

110.26(E) dedicated equipment space extends from the floor to 6 ft above the equipment or to structural ceiling, whichever is higher, and is reserved for the equipment served.

110.14(C) ampacity of conductors must be selected and coordinated so the lowest temperature-rated conductor, termination, or device is not exceeded.

Conductor ampacity adjustment factors (310.15) apply to current-carrying conductors; neutral counts as current-carrying only when it carries nonlinear harmonic current or is part of a 3-wire circuit with line-to-neutral loads.

Informational Notes in the NEC are explanatory only and are not enforceable as code requirements; only the mandatory text and referenced standards govern.

Chapter 3 wiring methods each have an Article: 320 armored cable, 330 metal-clad cable, 334 nonmetallic-sheathed cable, 338 service-entrance cable, 348 flexible metal conduit, 350 liquidtight flexible metal conduit, 352 PVC conduit, 358 EMT.

300.5 minimum cover for direct-buried conductors: 24 in for general use, 18 in for residential branch circuits at 120 V or less with GFCI, 12 in for 120 V landscape lighting, and 6 in for rigid metal conduit under a 4-in concrete slab.

300.5(D) requires a warning ribbon 12 in above buried service conductors and protection from physical damage where conductors emerge from grade.

334.30 NM cable must be secured within 12 in of boxes and supported at intervals not exceeding 4.5 ft; 334.17 requires protection where cable passes through framing members near the edge.

348.30 FMC must be secured within 12 in of boxes and supported at intervals not exceeding 4.5 ft; 348.60 requires an equipment grounding conductor where flexibility is needed or the raceway is over 6 ft.

352.30 PVC conduit support intervals: 3 ft for trade sizes 1/2 through 1, 5 ft for 1-1/4 through 2, and 10 ft for 2-1/2 and larger, with expansion fittings where thermal movement occurs.

358.30 EMT must be securely fastened within 3 ft of boxes and supported at intervals not exceeding 10 ft; 358.24 requires reaming of cut ends.

310.16 ampacity tables are based on 30 degrees C ambient; 310.15(B)(2)(a) correction factors apply for ambient temperatures above 30 degrees C.

210.52(A) dwelling receptacle spacing: no point along the floor line of a wall space is more than 6 ft from a receptacle outlet, and wall spaces 2 ft or wider require a receptacle.

210.52(C) countertop receptacles: no point on the countertop is more than 24 in from a receptacle, and at least one receptacle is required for each island or peninsula.

210.8 GFCI protection is required in dwelling bathrooms, garages, outdoors, kitchens, laundry areas, and within 6 ft of sinks; 210.12 AFCI protection covers dwelling branch circuits in most habitable rooms.

210.11(C)(3) requires at least one 20 A laundry branch circuit in dwellings; 210.11(C)(1) requires at least two 20 A small-appliance branch circuits in kitchens.

220.82 optional feeder/service calculation for dwellings: 100 percent of first 10 kVA plus 40 percent of the remainder of general load, plus nameplate ratings of appliances and motors.

220.12 general lighting load is 3 VA per square foot for dwellings and 1 VA per square foot for hospitals; 220.42 applies lighting demand factors.

220.54 electric clothes dryers are calculated at 5000 VA or nameplate, whichever is larger, with demand factors in Table 220.54 for multiple dryers.

210.19(A) branch-circuit conductors must have ampacity not less than the noncontinuous load plus 125 percent of the continuous load; 210.20 applies the same rule to overcurrent devices.

250.52 grounding electrode system includes metal underground water pipe (in contact with earth 10 ft or more), metal building frame, concrete-encased electrode, ground ring, rod/pipe electrodes, and plate electrodes.

250.66 sizes the grounding electrode conductor based on the largest service-entrance conductor; 250.122 sizes the equipment grounding conductor based on the overcurrent device rating.

250.53(A)(2) requires a supplemental electrode where a single rod, pipe, or plate electrode has a resistance to ground over 25 ohms; 250.53(A)(3) requires 6 ft minimum spacing between electrodes.

250.24(A)(5) prohibits using the grounded conductor for grounding on the load side of the service disconnect; 250.32 covers separate buildings and structures.

250.30 covers separately derived systems; the system bonding jumper connects the grounded conductor to the equipment grounding conductor at the source.

250.118 lists acceptable equipment grounding conductors, including copper conductors, rigid metal conduit, IMC, EMT, and listed liquidtight flexible metal conduit with internal grounding conductor.

250.148 requires continuity of the equipment grounding conductor at boxes and fittings; 250.134 requires bonding of metal raceways and enclosures.

250.102(C) sizes supply-side bonding jumpers based on the largest ungrounded supply conductor, using Table 250.102(C)(1).

240.4 general rule: conductors must be protected against overcurrent in accordance with their ampacities; 240.4(D) applies the small-conductor limits (14 AWG at 15 A, 12 AWG at 20 A, 10 AWG at 30 A for copper).

240.4(B) permits the next higher standard overcurrent device rating where the conductor ampacity does not correspond to a standard rating, subject to limits for 800 A and below.

240.6(A) standard ampere ratings include 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200 A.

240.21 lists tap conductor rules: 10 ft rule, 25 ft rule, and transformer secondary rules, each with specific ampacity and physical protection conditions.

430.52 motor branch-circuit short-circuit and ground-fault protection: inverse-time breaker at 250 percent of FLC, dual-element fuse at 175 percent, non-time-delay fuse at 300 percent.

240.86 series-rated systems require the combination of overcurrent devices to be listed and marked for the application; the sum of the ratings must not exceed the rating of the load-side device.

240.4(E) applies specific overcurrent protection rules for taps, transformer secondaries, and motor circuits that may permit conductor ampacity below the device rating.

110.9 interrupting rating: equipment must have an interrupting rating not less than the available fault current at its terminals.

430.6(A)(1) motor branch-circuit conductors must be sized at not less than 125 percent of the motor full-load current from Tables 430.248-430.250, not the nameplate current.

430.22 branch-circuit conductors must have ampacity of at least 125 percent of the motor full-load current; 430.24 feeder conductors use 125 percent of the largest motor plus 100 percent of the others.

430.32 overload protection: for motors over 1 hp, 115-125 percent of nameplate current for a marked service factor of 1.15 or higher, 115 percent for a marked temperature rise of 40 degrees C or less.

430.52 short-circuit protection may be increased to the next standard rating if the calculated value does not correspond to a standard size, but not above the maximum limits in Table 430.52.

430.102 requires a disconnecting means within sight of the motor and driven machinery; 430.103 requires the disconnect to open all ungrounded conductors.

440.32 and 440.33 cover hermetic refrigerant motor-compressor branch-circuit conductors and short-circuit protection; 440.6 requires nameplate rated-load current for sizing.

440.52 requires a disconnecting means for air-conditioning equipment within sight of and accessible from the equipment; 440.63 covers the disconnecting means for hermetic compressors.

430.72(B) covers overload protection for conductors; 430.28 applies tap conductor rules for motor branch circuits and feeders.

Article 500 classifies hazardous locations by Class I (gases and vapors), Class II (dusts), and Class III (fibers and flyings); Division 1 is normal conditions, Division 2 is abnormal conditions.

Article 505 uses Zones 0, 1, 2 for gases and Zones 20, 21, 22 for dusts; Zone 0 is continuous presence of flammable gas, Zone 1 is likely during normal operation.

Article 511 covers commercial garages and requires Class I, Division 2 classification for areas up to 18 in above the floor and within defined boundaries.

Article 514 covers motor fuel dispensing facilities, requiring Class I, Division 1 or 2 classification based on the area around dispensers and tanks.

Article 517 covers health care facilities; 517.18 requires hospital-grade receptacles and 517.19 covers critical branch circuits in patient care areas.

Article 680 covers swimming pools, fountains, and similar installations; 680.26 requires equipotential bonding of pool shells, decks, and metal parts.

Article 690 covers solar photovoltaic systems; 690.8 requires conductor ampacity of 125 percent of the maximum current, and 690.12 covers rapid shutdown requirements.

Article 695 covers fire pumps; 695.4 requires a reliable power source and 695.6 covers the dedicated fire pump feeder with specific overcurrent protection limits.

Article 700 covers emergency systems, Article 701 legally required standby systems, Article 702 optional standby systems, and Article 708 critical operations power systems.

700.12 requires an emergency source of power capable of supplying the emergency loads; 700.17 requires separation of emergency circuits from other circuits.

700.16 requires emergency illumination for at least 90 minutes; 700.23 covers the transfer of emergency loads to the alternate source.

Article 760 covers fire alarm systems; 760.41 and 760.43 cover non-power-limited and power-limited fire alarm circuits.

Article 725 covers Class 1, Class 2, and Class 3 remote-control, signaling, and power-limited circuits; Class 2 and 3 circuits are limited in power and voltage.

Article 680.25 requires an insulated equipment grounding conductor in feeders to pool equipment; 680.23 requires GFCI protection for underwater luminaires.

Article 547 covers agricultural buildings; 547.5 requires equipotential planes and 547.9 covers the equipotential bonding grid for livestock.

Article 500.8 requires equipment marking for the class, division, and group; Class I groups are A, B, C, D and Class II groups are E, F, G.

NFPA 70E covers electrical safety in the workplace; Article 130 covers work practices, including energized work permits and approach boundaries.

NFPA 70E arc flash PPE categories or incident energy analysis determine the required arc-rated clothing and equipment for energized work.

The limited approach boundary for 120-750 V is 10 ft for exposed movable conductors and 3 ft 6 in for fixed circuit parts; the restricted boundary is 1 ft for 120-750 V.

OSHA 29 CFR 1910 Subpart S adopts electrical safety requirements for general industry; 1910.333 covers selection and use of work practices.

Lockout/tagout under 1910.147 requires de-energization, verification of de-energization, and application of locks and tags before work.

The NEC is enforced by the authority having jurisdiction (AHJ) under 90.4; the AHJ interprets the code and grants approvals.

Inspection of electrical installations includes verifying grounding and bonding, overcurrent protection, working clearances, and listing of equipment under 110.3.

Test instruments for verification include low-resistance ohmmeters for grounding and insulation resistance testers; test results must be documented for compliance.