Chapter 4 of 518% of exam

Motors, HVAC Equipment, Luminaires and Power Production Sources

Motor circuits are the one place in the code where conductors, short-circuit protection and overload protection are all sized from different numbers and different percentages, which is exactly why the exam loves them. Once you accept that the table full-load current sizes almost everything except the overload, motor questions become routine arithmetic.

Motor Full-Load Current and Conductor Sizing

The full-load current tables in Article 430 are the required basis for conductor sizing, branch-circuit short-circuit protection and disconnect ratings, no matter what the motor nameplate says. This is deliberate, because the code wants a consistent installation even if the motor is later replaced with a different brand. Nameplate current is reserved for overload protection, where the goal is protecting that specific machine.

Use the tables
Table 430.248 for single-phase and Table 430.250 for three-phase motors supply the full-load current used for conductor, protection and disconnect sizing.
2023 NEC §430.6(A)(1)
Single motor conductors
Branch-circuit conductors for a single continuous-duty motor must have an ampacity of at least 125 percent of the table full-load current.
2023 NEC §430.22
Several motors on one feeder
Feeder conductors must carry 125 percent of the largest motor full-load current plus the sum of the full-load currents of all other motors.
2023 NEC §430.24
Disconnect rating
The disconnecting means must have an ampere rating of at least 115 percent of the motor full-load current.
2023 NEC §430.110(A)
Disconnect location
A disconnect must be in sight from the controller, and in sight from the motor and driven machinery unless it is capable of being individually locked open.
2023 NEC §430.102

Overload Versus Short-Circuit Protection

These are two separate devices doing two separate jobs, and confusing them is the classic motor mistake. Overload protection responds slowly to modest sustained overcurrent that would cook the windings, and it is sized from the nameplate. Short-circuit and ground-fault protection responds quickly to a fault while still letting the motor draw its large starting current, so its percentages are far higher.

Overload at 125 percent
Motors with a marked service factor of 1.15 or greater, or a marked temperature rise not over 40 degrees C, may be protected at up to 125 percent of nameplate full-load amperes.
2023 NEC §430.32(A)(1)
Overload at 115 percent
All other continuous-duty motors over 1 horsepower are limited to 115 percent of nameplate full-load amperes.
2023 NEC §430.32(A)(1)
Permitted increase
Where the overload device will not allow the motor to start or carry the load, it may be increased to 140 percent for the better-rated motors and 130 percent for all others.
2023 NEC §430.32(C)
Branch-circuit protection percentages
For a squirrel-cage motor: non-time-delay fuse 300 percent, dual-element time-delay fuse 175 percent, inverse-time breaker 250 percent, instantaneous-trip breaker 800 percent of full-load current.
2023 NEC Table 430.52(C)(1)
Next standard size
Where the calculated protection value does not correspond to a standard rating, the next higher standard size is permitted.
2023 NEC §430.52(C)(1)
Feeder protection ceiling
A feeder overcurrent device must not exceed the largest branch-circuit protective device plus the sum of the full-load currents of the other motors.
2023 NEC §430.62(A)

Air Conditioning and Refrigeration Equipment

Article 440 equipment is factory engineered, so the nameplate does most of the work for you. Minimum circuit ampacity sets the conductor and maximum overcurrent protective device sets the ceiling on the breaker or fuse, and neither number may be adjusted upward in the field. When you must calculate rather than read a nameplate, hermetic compressors use rated-load current with their own percentages.

Nameplate marking
Equipment must be marked with the minimum circuit ampacity and the maximum rating of the branch-circuit short-circuit and ground-fault protective device.
2023 NEC §440.4(B)
Conductor sizing
Conductors to a single motor-compressor must have an ampacity of at least 125 percent of the rated-load or branch-circuit selection current.
2023 NEC §440.32
Short-circuit protection
Protection is sized at not more than 175 percent of rated-load current, increased only where necessary to start the equipment and never above 225 percent.
2023 NEC §440.22(A)
Disconnect rating
The disconnecting means must be rated at least 115 percent of the sum of the rated-load currents or branch-circuit selection currents.
2023 NEC §440.12(A)
Disconnect location
The disconnecting means must be readily accessible and located within sight from the air conditioning or refrigerating equipment.
2023 NEC §440.14

Luminaires and Lighting Outlets

Luminaire rules concentrate on heat and on the specific hazard of clothes closets, where stored fabric can rest against a hot fixture. Recessed luminaires add the problem of blown-in insulation packed around a housing that was never designed for it, which is why the IC rating exists. Support requirements make sure the fixture weight is carried by the structure and not by the wiring.

Clothes closet clearances
Surface-mounted luminaires with a completely enclosed light source require 12 inches from the storage space, while recessed types with an enclosed light source require 6 inches.
2023 NEC §410.16(C)
Open lamps prohibited
Incandescent luminaires with open or partially enclosed lamps are not permitted in clothes closets.
2023 NEC §410.16(B)
Non-IC recessed clearances
A recessed luminaire not identified for insulation contact must be spaced at least 1/2 inch from combustible materials and 3 inches from thermal insulation.
2023 NEC §410.116
Support
Luminaires weighing more than 6 pounds or exceeding 16 inches in any dimension must not be supported by the screw shell of a lampholder.
2023 NEC §410.30
Boxes supporting luminaires
An outlet box used as the sole support of a luminaire must be listed and marked for the maximum weight it will carry.
2023 NEC §314.27(A)

Generators and Photovoltaic Systems

On-site power sources appear on the exam in small numbers but with predictable questions about conductor sizing and disconnection. Generator output conductors are uprated rather than derated because the machine itself limits the available current. Photovoltaic circuits apply the 125 percent factor twice, once to establish the maximum circuit current and again to size conductors and protection.

Generator output conductors
Conductors from generator terminals to the first overcurrent device must have an ampacity of at least 115 percent of the nameplate current rating.
2023 NEC §445.13(A)
Generator disconnect
Generators must have a disconnecting means that simultaneously opens all associated ungrounded conductors, with limited exceptions.
2023 NEC §445.18
Photovoltaic maximum circuit current
The maximum current of a PV source circuit is 125 percent of the rated short-circuit current of the modules.
2023 NEC §690.8(A)
Photovoltaic conductor sizing
Conductors and overcurrent devices are sized at not less than 125 percent of the maximum circuit current before applying adjustment and correction factors.
2023 NEC §690.8(B)
Rapid shutdown
PV systems on buildings must have a rapid shutdown function to reduce conductor voltage within the array boundary for firefighter safety.
2023 NEC §690.12
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Last updated: July 2026

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