I have a 30 amp circuit breaker installed for my tank type hot water heater. I would like to replace the hot water heater with a tankless hot water heater that requires a 40 amp circuit breaker. I don’t know the gauge of wiring used for the circuit breaker but is it possible to just replace the 30 amp breaker with a 40 amp breaker?
Electrical – replace a 30A breaker with a 40A breaker for a new water heater
electrical
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Best Answer
Your current 30A water heater circuit was probably wired with #10 solid copper. You can confirm this by inspecting the stamp or printing on the cable jacket, or by using a gauge measuring tool (with the power safely disconnected).
A 40A circuit typically calls for #8 copper wire, which is usually stranded. It's a markedly larger cable bundle. If you don't have that, DO NOT increase the breaker size. A circuit breaker's primary function is to protect wiring from overload, and a 40A breaker does not adequately protect #10 wire.
This is standard advice and doesn't apply to inordinately long runs or other nonstandard scenarios which may call for even larger wire.