6.2 General Use Equipment & Appliances (0502)

Appliance Branch Circuits and Disconnecting Means (NEC Article 422)

An appliance is utilization equipment generally other than industrial, normally built in standardized sizes or types, that performs one or more functions such as clothes washing or food mixing.

Branch-Circuit Sizing (422.10)

An appliance is connected to a branch circuit sized to the appliance nameplate marking. Where the appliance is a continuous load, the branch-circuit conductor and overcurrent device are sized at 125% of the marked rating — which is the same rule as loading a circuit to no more than 80% of its rating, stated from the other direction. 422.11 sets the overcurrent protection: an appliance branch circuit must be protected in accordance with 422.11(A) through (G), and where a protective device rating is marked on the appliance, the branch-circuit device shall not exceed that marking.

Disconnecting Means (422.30 - 422.35)

The field question is almost always the same: can the technician safely kill this appliance from where they are standing? If the branch-circuit device is out of sight and not lockable, add a disconnect at the appliance.

Fixed Electric Space Heating (NEC Article 424)

Fixed electric space heating includes baseboard, cable, duct, and unit heaters. NEC 424 treats the load as continuous:

• 424.3(A) Individual branch circuits — an individual branch circuit is permitted to supply any size fixed electric space-heating equipment; branch circuits supplying two or more outlets for fixed electric space-heating equipment shall be rated 15, 20, 25, or 30 amperes.
• 424.3(B) Branch-circuit sizing — fixed electric space-heating equipment and its associated motors are treated as a continuous load. The branch-circuit conductors and the overcurrent device must be sized at not less than 125% of the total heating and motor load. Read the direction carefully: 125% of the load, which is the same thing as loading the circuit to no more than 80% of its rating.
• 424.22 Overcurrent protection — the branch-circuit device must not exceed the maximum marked on the equipment, and resistance-type heating elements in electric space-heating equipment must be subdivided into loads not exceeding 48 A and protected at not more than 60 A. That subdivision rule is why a large duct heater arrives from the factory with several internal fuse blocks.

Air-Conditioning and Refrigeration (NEC Article 440)

Article 440 covers electrically driven air-conditioning and refrigerating equipment that has a motor-compressor. The rules modify and supplement Article 430.

Disconnecting Means (440.11 / 440.12)

• 440.11 — the disconnecting means for a motor-compressor shall be capable of being locked in the open position and shall interrupt the locked-rotor current of the motor-compressor.
• 440.12(A) Single motor-compressor — the disconnect must have an ampere rating not less than 115% of the nameplate rated-load current or branch-circuit selection current, whichever is greater, and a horsepower rating derived from the locked-rotor current using Tables 430.251(A) and (B).
• 440.12(B) Combination loads — for a disconnect serving a motor-compressor and other loads, the ampere rating is the sum of the motor-compressor load and the other loads.

Branch-Circuit OCPD and Conductor Sizing

• 440.4(B) Maximum OCPD marked — where the equipment nameplate marks a maximum branch-circuit OCPD, the installed OCPD shall not exceed that value.
• 440.22(A) Device sizing — the branch-circuit short-circuit and ground-fault protective device must be capable of carrying the starting current. A device rating not exceeding 175% of the motor-compressor rated-load current or branch-circuit selection current (whichever is greater) is deemed to comply; where that rating is not sufficient to carry the starting current, it may be increased but shall not exceed 225%. Where the calculated value does not correspond to a standard size, 440.22(A) directs you to the next lower standard rating — the opposite of the usual round-up habit.
• 440.32 / 440.33 Conductors — branch-circuit conductors supplying a single motor-compressor must have an ampacity not less than 125% of the rated-load current or branch-circuit selection current, whichever is greater (440.32). Where a motor-compressor is on a circuit with other loads (a condenser fan, a crankcase heater), 440.33 requires 125% of the largest motor-compressor rating plus the sum of the rated-load or full-load currents of the other motors and loads.

Worked Example: A/C Circuit Sizing

A 240 V air conditioner has a motor-compressor rated-load current of 24 A and a 1 A condenser fan on the same branch circuit. The nameplate does not mark a maximum overcurrent device.

1. Branch-circuit conductor ampacity (440.33): 125% × 24 A + 1 A = 30 + 1 = 31 A → from Table 310.16, #10 AWG copper at 75 °C (35 A) is the minimum.
2. Branch-circuit short-circuit and ground-fault device (440.22(A)): start at 175% — 1.75 × 24 = 42 A. That is not a standard size, and 440.22(A) sends you to the next lower standard rating, so the device is 40 A. Only if a 40 A device will not carry the starting current may it be increased, and then not beyond 225% × 24 = 54 A, which after rounding down lands on 50 A. A candidate who jumps straight to 225% and rounds up to 60 A has made two errors in one step.
3. Disconnect rating (440.12(B)): 115% × 24 A + 1 A ≈ 29 A minimum, with a horsepower rating derived from the locked-rotor current — in practice a 60 A disconnect switch.
4. 440.4(B) — if the nameplate had marked a maximum overcurrent protective device, that marked value would govern and override every calculation above.

Room A/C Cord Connection (440.60 - 440.65)

A room air conditioner may be cord-connected when it is rated not over 40 A and 250 V, single phase (440.62(A)); the attachment plug and receptacle may serve as the disconnecting means. 440.64 limits the supply cord length to 10 ft for a nominal 120 V supply and 6 ft for a nominal 208 or 240 V supply. Where the unit is the only load on the circuit, its marked rating may not exceed 80% of the branch-circuit rating; where lighting or other appliances share the circuit, that drops to 50% (440.62(B) and (C)). 440.65 requires the cord to have a listed leakage-current detector-interrupter (LCDI) or arc-fault circuit interrupter (AFCI) integral to the attachment plug or within 12 in. of it.