30 Amp Breaker: Wire Size and Uses
Common uses for a 30A breaker
Electric dryers, water heaters, small AC units. 10 AWG limited to 30A per NEC 240.4(D). Most common 240V residential circuit.
The 30A/240V breaker is the standard for electric dryers and water heaters. It uses a double-pole breaker that occupies two slots in the panel. The NEMA 14-30R receptacle (4-prong dryer outlet) is the standard for this circuit. New dryer circuits must be 4-wire (two hots, neutral, ground) per NEC 250.140.
Wire size for a 30A breaker
The wire must have an ampacity that meets or exceeds the breaker rating at the appropriate temperature column. Here are the minimum wire sizes:
| Material | Minimum wire | Details |
|---|---|---|
| Copper | 10 AWG | Standard for residential branch circuits |
| Aluminum | 8 AWG | Common for feeders and above and larger |
These sizes assume 75°C termination temperature per NEC 110.14(C), which is the standard for most residential breakers and devices. For long wire runs, check voltage drop - you may need to upsize the wire even though the ampacity is adequate.
Continuous load rule (80% maximum)
For continuous loads - any load expected to run for 3 hours or more - the NEC requires that the load not exceed 80% of the breaker rating (NEC 210.20(A)). On a 30A breaker, the maximum continuous load is 24A.
This is why sizing often seems counterintuitive:
- A 24A continuous water heater requires a 30A breaker (24 × 1.25 = 30A)
- Non-continuous loads can use the full 30A capacity
- 100% rated breakers exist but are rare in residential panels - assume 80% unless the breaker is specifically listed as 100% rated
Installation notes
Breaker type: A 30A breaker is a double-pole (240V) breaker. Double-pole breakers occupy two adjacent slots in the panel and provide 240V between the two hot conductors. Both poles must trip simultaneously - never use two single-pole breakers tied together with a handle tie for 240V circuits (except as explicitly allowed for specific multi-wire branch circuits).
Ground wire: A 30A circuit requires a minimum 10 AWG copper equipment grounding conductor per NEC Table 250.122.
Standard sizes: 30A is a standard breaker size per NEC 240.6(A). Standard residential breaker sizes are: 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200. Non-standard sizes should never be used.
Why does my 30A breaker keep tripping?
A 30A breaker tripping on a dryer circuit usually means one of two things: the heating element has a partial short to ground (causing a ground fault that trips GFCI-protected circuits), or the vent is clogged and the thermal fuse keeps cycling the element on and off rapidly. Start with the vent - a clogged dryer vent causes the element to overheat and draw more current. For water heaters, a tripping 30A breaker often indicates a failing heating element where the nichrome wire has cracked and is arcing to the tank wall.
Frequently asked questions
What wire size for a 30 amp breaker?
10 AWG copper or 8 AWG aluminum minimum. The wire must have an ampacity at the 75°C column that meets or exceeds 30A. For long runs, you may need to upsize for voltage drop.
What can a 30 amp breaker handle?
Electric dryers, water heaters, small AC units. For continuous loads (3+ hours), the maximum is 24A (80% of 30A). For non-continuous loads, the full 30A is available.
Can I put a 30A breaker on 10 AWG wire?
The breaker must not exceed the wire ampacity. 10 AWG copper supports a 30A breaker. Never put a larger breaker on wire that cannot handle it - this defeats the safety purpose of the breaker.
Is 30A a standard breaker size?
Yes. 30A is a standard breaker size per NEC 240.6(A). It is widely available from all major breaker manufacturers (Square D, Eaton, Siemens, GE). Always use the correct breaker brand for your panel - breakers are not interchangeable between panel brands.
Related guides
- 30A wire sizing guide - complete sizing with voltage drop
- Ground wire for 30A circuit
- 10 AWG copper ampacity - derating and conduit fill
- 10 AWG copper vs aluminum
- NEC Article 240: Overcurrent protection
- Ampacity calculator
What to buy
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NEC 2023 references verified April 2026