13.2 Appliances & Fixed Electric Space Heating (NEC Articles 422 & 424)

13.2 Appliances & Fixed Electric Space Heating (NEC Articles 422 & 424)

Exam Focus: 422.10 branch-circuit rating, 422.13 water heater continuous load, 422.16 cord lengths, 422.31/422.33 disconnecting means, 424.3(B) heating as continuous load, 424.44(G) heated floor GFCI, and Article 440 nameplate MCA/MOP.

Appliances is a named subject on the PSI blueprint. The rules divide cleanly into three: how big the circuit must be, how the appliance may be connected, and how it is disconnected for service.

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Sizing the Appliance Branch Circuit — Article 422 Part II

The Two Continuous-Load Classifications

+-------------------------------------------------------------------------+
|            APPLIANCES THE CODE CALLS CONTINUOUS LOADS                   |
|                                                                         |
|   422.13  Fixed STORAGE-TYPE WATER HEATER, 120 gallons or less          |
|           --> branch circuit sized at 125% of nameplate rating          |
|                                                                         |
|   424.3(B) FIXED ELECTRIC SPACE-HEATING EQUIPMENT                       |
|           --> conductors and OCPD at 125% of total heating load,        |
|               including any motors                                      |
|                                                                         |
|   Example: a 4,500 W, 240 V water heater draws 18.75 A.                 |
|   18.75 x 1.25 = 23.4 A --> 25 A OCPD, 10 AWG copper conductors.        |
+-------------------------------------------------------------------------+

[!CAUTION] The 120-gallon threshold is exact. A storage water heater of 120 gallons or less is a continuous load. A larger commercial storage heater is not automatically classified that way by 422.13, though it may still be a continuous load in fact under the Article 100 three-hour definition.

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Flexible Cord Connection — NEC 422.16

Cord-and-plug connection is a permitted method for specific appliances, with specific cord lengths that examiners like because they are exact numbers.

Measurement trap: the dishwasher and compactor length is measured to the plane of the rear of the appliance, not to the terminal box. Options that describe the measurement any other way are wrong.

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Appliance Disconnecting Means — Article 422 Part III

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Fixed Electric Space Heating — Article 424

Worked Example

A dwelling has 12 kW of baseboard electric heat plus a 5 A blower motor, supplied at 240 V.

1. Heating current: $12{,}000 / 240 = 50\ \text{A}$
2. Add the motor: $50 + 5 = 55\ \text{A}$
3. Apply 424.3(B): $55 \times 1.25 = 68.75\ \text{A}$
4. Minimum overcurrent device: 70 A, with conductors of at least 68.75 A ampacity at the applicable terminal temperature column.

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Air Conditioning and Refrigeration — Article 440 Nameplate Rules

Hermetic refrigerant motor-compressors do not follow the general motor rules of Article 430. Instead, the equipment nameplate carries two numbers that override the usual calculations:

The MOP commonly exceeds what 240.4(D) would allow for the conductor size, which is one of the specific exemptions listed in 240.4(G). A 14 AWG conductor with an MCA of 14.2 A and an MOP of 25 A is a legitimate installation on a 25 A device — the fuse or breaker is providing short-circuit and ground-fault protection while the compressor's internal overload protects against overload.

2023 reminder: an outdoor condensing unit outlet in a dwelling requires GFCI protection under 210.8(F), and the outdoor emergency disconnect and surge protection rules in Section 10.4 apply to the dwelling service that feeds it.