12.3 Appliances & Electric Water Heaters (NEC Article 422)
Key Takeaways
- Under NEC 422.13, all electric storage-type water heaters having a capacity of 120 gallons (450 L) or less are classified as continuous loads, requiring branch circuit conductors and overcurrent protective devices (OCPD) to be sized at not less than 125% of the nameplate current rating.
- A standard 240V, 4500W residential electric storage water heater draws 18.75A; applying the 125% continuous load multiplier yields 23.44A, which mandates a 30A circuit breaker and #10 AWG copper conductors.
- Under NEC 422.30 and 422.31, each appliance must be provided with a disconnecting means; if not within sight of the appliance (visible and within 50 feet), the branch circuit breaker must be capable of being locked in the open position with a permanent locking provision remaining in place with or without the lock per NEC 110.25.
- Flexible cord connections under NEC 422.16(B) are permitted for specific built-in appliances: kitchen waste disposers require cord lengths between 18 and 36 inches, while built-in dishwashers require cord lengths between 3.0 and 6.5 feet, with receptacles located in adjacent spaces.
- Under NEC 210.23(A)(2) and 422.10(B), fastened-in-place appliances on a 15A or 20A multi-outlet branch circuit supplying lighting or portable loads cannot exceed 50% of the circuit rating (10A on a 20A circuit), while any portable cord-and-plug appliance cannot exceed 80% (16A on a 20A circuit).
Appliances & Electric Water Heaters (NEC Article 422)
NEC Article 422 governs the electrical installation, branch circuit sizing, overcurrent protection, and disconnecting means for electrical appliances used in residential, commercial, and industrial occupancies. Appliances range from small cord-and-plug kitchen devices to heavy fixed equipment like electric water heaters, commercial dishwashers, and trash compactors. Understanding the precise sizing calculations, continuous load mandates, and lockout disconnect rules is essential for the Oklahoma Journeyman Electrician examination.
1. Branch Circuit Sizing for Appliances (NEC 422.10)
Branch circuit conductors supplying appliances must have an allowable ampacity not less than the marked appliance rating or the calculated load under Article 220.
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| APPLIANCE BRANCH CIRCUIT SIZING PROTOCOLS |
| |
| CIRCUIT TYPE CODE REFERENCE SIZING RULE & CONDUCTOR AMPACITY MANDATES |
| --------------------- --------------- -------------------------------------------------------- |
| Individual Branch NEC 422.10(A) Must not be less than the appliance marked nameplate |
| Circuit rating. For continuous loads (>= 3 hours), branch circuit|
| conductors & OCPD must be sized at >= 125% of load. |
| |
| Multi-Outlet Branch NEC 422.10(B) & - Fastened-in-place appliances: <= 50% of circuit rating |
| Circuit NEC 210.23(A) when circuit also supplies lighting or portable loads. |
| - Portable cord-and-plug loads: <= 80% of circuit rating.|
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2. Electric Storage-Type Water Heaters (NEC 422.13)
One of the most frequently tested sizing questions on the Journeyman exam involves electric water heaters. Storage water heaters continuously maintain water temperature around the clock, creating prolonged thermal stress on branch circuits.
NEC 422.13 Rule: "All fixed electric storage-type water heaters having a capacity of 120 gallons (450 L) or less shall be considered a continuous load for the purpose of sizing branch circuits."
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| WATER HEATER CALCULATION WORKFLOW (NEC 422.13) |
| |
| STEP 1: Calculate Full-Load Nameplate Current |
| I_nameplate = Power (Watts) / Voltage (Volts) |
| |
| STEP 2: Apply 125% Continuous Load Multiplier (NEC 422.13 / 210.19(A)(1)) |
| Minimum Conductor & OCPD Ampacity = I_nameplate × 1.25 |
| |
| STEP 3: Select Standard Overcurrent Device (NEC 240.6) |
| Choose standard breaker/fuse >= calculated minimum ampacity. |
| |
| STEP 4: Size Copper Conductors (NEC Table 310.16 & 240.4(D)) |
| Select conductor with ampacity matching circuit rating. |
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Comprehensive Calculation: Standard 4,500W Residential Water Heater
A single-family residence has a 50-gallon, 4,500-Watt, 240-Volt electric storage water heater:
- Full-Load Current:
- Minimum Circuit Ampacity (125% continuous rule):
- Overcurrent Protective Device Selection:
- Under NEC 240.6(A), the next standard protective device size above 23.44A is 30 Amperes (a 25A breaker could protect 23.44A, but water heater circuits traditionally standardize on 30A).
- Conductor Sizing:
- Under NEC Table 310.16 and Small Conductor Rules (NEC 240.4(D)), #10 AWG copper (rated 30A at 75°C/60°C) is required.
Water Heater Sizing Comparison Table:
| Water Heater Rating | Voltage | Full-Load Current | Min. Ampacity (125%) | Min. OCPD Rating | Min. Conductor Size (Cu) |
|---|---|---|---|---|---|
| 3,000 Watts | 240V | 12.50 A | 15.63 A | 20 Amperes | #12 AWG Cu |
| 3,800 Watts | 240V | 15.83 A | 19.79 A | 20 Amperes | #12 AWG Cu |
| 4,500 Watts | 240V | 18.75 A | 23.44 A | 30 Amperes | #10 AWG Cu |
| 5,500 Watts | 240V | 22.92 A | 28.65 A | 30 Amperes | #10 AWG Cu |
| 12,000 Watts (3Ø) | 208V | 33.31 A | 41.64 A | 50 Amperes | #8 AWG Cu |
3. Disconnecting Means for Appliances (NEC 422.30–422.35)
A disconnecting means is mandatory for each appliance to ensure service technicians can safely de-energize equipment without risking accidental re-energization.
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| APPLIANCE DISCONNECT RULES (NEC 422.31) |
| |
| APPLIANCE RATING DISCONNECT LOCATION PERMITTED DISCONNECTING MEANS |
| --------------------- -------------------------------- --------------------------------------- |
| <= 300 VA or <= 1/8 hp Branch circuit switch or breaker Branch circuit breaker or switch. |
| (422.31(A)) Need not be within sight or lockable. |
| |
| > 300 VA or > 1/8 hp Within Sight OR Lockable Circuit 1. Disconnect switch within sight |
| (Without Motor) Breaker (NEC 422.31(B)) (within 50 ft & visible), OR |
| 2. Branch breaker with permanent lockout|
| provision complying with NEC 110.25. |
| |
| Motor-Driven Within Sight of Motor Controller 1. Disconnect within sight of motor |
| > 1/8 hp (NEC 422.31(C)) controller, OR |
| 2. Lockable breaker complying with 110.25|
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Lockout/Tagout Compliance Under NEC 110.25:
- When a branch circuit breaker serves as the disconnecting means for an appliance located out of sight (e.g., an electric water heater in a basement while the electrical panel is in the garage), the locking provision must be installed on or at the switch or circuit breaker and must remain in place with or without the lock installed.
- Portable clip-on or snap-on lockout hasps carried in a tool bag do not satisfy NEC 110.25!
Other Permitted Disconnecting Means:
- Unit Switches (NEC 422.34): A unit switch with a marked "OFF" position that disconnects all ungrounded conductors is permitted as the disconnect if other disconnecting means (e.g., service switch, panel breaker) exist in the building.
- Cord-and-Plug Connections (NEC 422.33): For cord-and-plug connected appliances, an accessible separable connector or attachment plug and receptacle is an approved disconnecting means.
4. Flexible Cord Connections for Built-in Appliances (NEC 422.16(B))
[!IMPORTANT] Oklahoma adds a fifth item to this list. OAC 748:20-10-10 adopts NEC Chapter 4 with an added 422.16(B)(5), permitting a gas-fired central furnace supplying a dwelling unit to be cord-and-plug connected so the homeowner can move it onto a portable generator. The cord must contain an equipment grounding conductor and terminate in a grounding-type attachment plug, must have sufficient ampacity for the load, must be routed or protected against physical damage, and must not exceed 9 feet. See Section 1.6.
Specific built-in household appliances are permitted to be cord-and-plug connected rather than hardwired, provided strict dimensional and safety rules are satisfied:
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| CORD-AND-PLUG APPLIANCE SPECIFICATIONS (NEC 422.16(B)) |
| |
| APPLIANCE CORD LENGTH RECEPTACLE LOCATION & SPECIAL MANDATES |
| -------------------- ------------------------- ----------------------------------------------- |
| Kitchen Waste 18 in. to 36 in. - Receptacle located in under-sink space. |
| Disposer (450 mm to 900 mm) - Grounding-type attachment plug required. |
| (422.16(B)(1)) - Cord protected from physical damage. |
| |
| Built-in 3.0 ft to 6.5 ft - Receptacle in space adjacent to dishwasher |
| Dishwasher (0.9 m to 2.0 m) (e.g., under adjacent sink cabinet). |
| (422.16(B)(2)) - Opening in partition must have smooth edges. |
| - Receptacle must be accessible. |
| |
| Trash 3.0 ft to 4.0 ft - Receptacle in space adjacent to compactor. |
| Compactor (0.9 m to 1.2 m) - Grounding-type attachment plug required. |
| (422.16(B)(2)) |
| |
| Wall-Mounted Ovens / Manufacturer-specified - Cord must terminate in grounding attachment |
| Counter Cooktops flexible cord assembly plug; receptacle accessible. |
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5. Appliance Overcurrent Protection (NEC 422.11)
Appliances must be protected against overcurrent in accordance with their nameplate ratings:
- Marked Rating: If a protective device rating is marked on the appliance nameplate (e.g., "Max Fuse or HACR Breaker: 25A"), the branch circuit OCPD rating shall not exceed the marked value.
- Non-Motor Appliances (NEC 422.11(E)): If not marked and the appliance is rated at $13.3\text{A}$ or less, the OCPD shall not exceed $20\text{A}$. If rated over $13.3\text{A}$, the OCPD shall not exceed 150% of the appliance rating, rounded up to the next standard rating if 150% does not correspond to a standard size.
A residential electric storage water heater has a nameplate rating of 4,500 Watts at 240 Volts single-phase and a tank capacity of 50 gallons. What is the minimum rating of the branch circuit overcurrent protective device and the minimum copper conductor size required under NEC 422.13, 210.19(A)(1), and Table 310.16?
An electric water heater is installed in a residential basement utility closet located 75 feet away and out of sight from the main electrical panelboard in the garage. What disconnecting means requirement must be met under NEC 422.31(B) and NEC 110.25?
An electrician is installing a cord-and-plug connection for a residential kitchen waste food disposer under a kitchen sink. Under NEC 422.16(B)(1), what are the permitted flexible cord length and termination requirements?
A 20-ampere 120-volt multi-outlet branch circuit in a commercial breakroom supplies convenience receptacles and lighting outlets. An electrician is installing a fastened-in-place commercial coffee brewer on this same circuit. Under NEC 210.23(A)(2) and 422.10(B), what is the maximum full-load current rating permitted for this fastened-in-place appliance?