Chapter 4 of 622% of exam

Equipment and Systems

This chapter covers how the Code sizes conductors and protection for specific loads and systems, from motors and HVAC to transformers, lighting, generators, solar, pools, and low-voltage work. Each equipment type has its own article with sizing multipliers and protection rules that override the general wiring chapters.

Motors (Article 430)

Motor circuits are unusual because the conductor, the overload device, and the branch-circuit short-circuit protection are each sized differently and from different tables. Conductors are sized from the motor's full-load current value in the Code tables rather than the nameplate current, while overloads protect from the nameplate. Understanding which value feeds which calculation is the key to passing motor questions.

Use table FLC for conductors
Branch-circuit conductor sizing and the ampacity basis use the full-load current from the Code tables, not the motor nameplate amps.
2023 NEC §430.6
Single motor conductor 125%
Conductors supplying a single continuous-duty motor must have an ampacity of at least 125 percent of the motor full-load current.
2023 NEC §430.22
Overload set from nameplate
Running overload protection is generally set at 115 to 125 percent of the motor nameplate full-load amperes depending on service factor and temperature rise.
2023 NEC §430.32
Branch short-circuit protection
Short-circuit and ground-fault protection is sized larger than the conductor, using percentage limits from the Code table based on device type such as inverse-time breaker or fuse.
2023 NEC §430.52
Disconnect rating
The motor disconnecting means must be at least 115 percent of the motor full-load current rating.
2023 NEC §430.110
Disconnect within sight
A disconnecting means must be located in sight from the motor location and the driven machinery, unless capable of being locked open.
2023 NEC §430.102

HVAC and Air Conditioning (Article 440)

Sealed hermetic-motor equipment such as air conditioners and heat pumps uses its own article that layers on top of the general motor rules. The nameplate provides two engineered numbers, the minimum circuit ampacity and the maximum overcurrent protection, that installers must respect exactly rather than calculating from scratch.

MCA sizes conductors
The minimum circuit ampacity on the equipment nameplate sets the smallest conductor ampacity permitted for the branch circuit.
2023 NEC §440.32
MOCP sizes protection
The maximum overcurrent protective device value on the nameplate is the largest fuse or breaker allowed and must not be exceeded.
2023 NEC §440.22
Rated-load current
For hermetic compressor motors, the rated-load current marked on the nameplate is used in place of the standard full-load current tables.
2023 NEC §440.6
Disconnect in sight of unit
A readily accessible disconnecting means must be located within sight from the air-conditioning or refrigerating equipment.
2023 NEC §440.14

Transformers and Lighting (Articles 450 and 410)

Transformers are protected on the primary and sometimes the secondary using percentage limits that depend on the protection scheme chosen. Luminaires and their wiring follow Article 410, which governs support, clearances from combustibles, and the temperature rating of conductors entering fixtures.

Primary-only protection
A transformer protected on the primary only generally uses an overcurrent device rated not more than 125 percent of the primary current for larger units.
2023 NEC §450.3
Working space at transformer
Dry-type transformers must maintain required clearances for ventilation and the general working space rules apply for access and heat dissipation.
2023 NEC §450.9
Recessed fixture clearances
Non-Type-IC recessed luminaires must maintain a half-inch clearance from combustible materials and be kept clear of thermal insulation.
2023 NEC §410.116
Luminaire as raceway
Luminaires may only be used as a raceway for circuit conductors when they are listed and marked for that use.
2023 NEC §410.64
Support of luminaires
Luminaires and lampholders must be securely supported, and a fixture weighing more than 6 pounds or exceeding 16 inches cannot rely on the screw shell alone.
2023 NEC §410.30

Generators, Standby, and Transfer Switches (Articles 445, 700, 702)

Standby and emergency power systems combine a source such as a generator with a transfer switch that prevents the utility and generator from ever being connected at the same time. Emergency systems that protect life safety carry stricter wiring separation and testing rules than optional standby systems that merely serve convenience loads.

Generator conductor ampacity
Conductors from a generator terminal to the first overcurrent device must have an ampacity of at least 115 percent of the nameplate current rating.
2023 NEC §445.13
Transfer switch prevents interconnection
Transfer equipment must be identified for the purpose and designed so the normal and alternate sources cannot be connected to the load at the same time.
2023 NEC §702.6
Emergency wiring kept separate
Wiring for emergency circuits must be kept independent of all other wiring except at transfer points and enclosures shared by design.
2023 NEC §700.10
Optional standby scope
Optional standby systems serve loads whose failure is an inconvenience rather than a life-safety hazard and are not legally required for occupancy.
2023 NEC §702.2

Solar, Pools, and Low-Voltage (Articles 690, 680, 725, 760, 800)

Special systems each add their own protections layered on the general Code. Photovoltaic arrays manage direct-current strings and rapid shutdown, swimming pools rely on equipotential bonding to eliminate voltage gradients, and Class 2 and communications circuits use power-limited sources that change the wiring and separation rules.

PV rapid shutdown
Photovoltaic systems on buildings must include a rapid shutdown function that reduces conductor voltage inside the array boundary to a safe level for firefighters.
2023 NEC §690.12
Pool equipotential bonding
An 8 AWG solid copper bonding conductor must tie together pool reinforcing steel, metal fittings, equipment, and the perimeter surface to equalize potential.
2023 NEC §680.26
Class 2 power-limited
Class 2 circuits are limited in voltage and power by their listed source, which provides the primary protection against shock and fire ignition.
2023 NEC §725.60
Fire alarm circuit integrity
Fire alarm circuits must be installed and supported so that the reliability of the life-safety system is maintained.
2023 NEC §760.24
Communications bonding
Communications cables entering a building must have their metallic sheath and protectors bonded to the building grounding electrode system.
2023 NEC §800.100
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Last updated: July 2026

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