20 amp breaker 12AWG wire to water heater

My 80 gallon electric water heater (Bedminster, NJ) has worked fine for years with low-wattage elements (not sure exact rating) on a 110V supply. Wire feeding the heater never rises above room temperature; breaker never trips. I’m told by a plumber that I must upgrade to a 30 amp 220V circuit to pass code when installing a new water heater. Is this so?

Why don’t you ask your local municipality? Cades are adopted, modified and enforced by the jurisdiction you live in.



I can’t ever recall seeing a 120v electric water heater. Except for the small ones you see under sinks.

Are you sure that it’s 120 volts? How many watts is the heater? A 4500 watt HWH draws 18.75 amps although it’s not code compliant it will run forever on a 20 amp circuit

Robert, wouldn’t it still work on 120, but take forever to heat the water? Like a 240 welder on 208, the welder still works, but you have to put the setting slightly higher.

My mistake. The breaker takes up two slots, so it’s not 110. I’m clearly no expert :expressionless:
I placed low wattage elements in it some time ago after a plumber replaced failed elements with high wattage units that heated the water, but also uncomfortably warmed the romex leading to the heater and provided an aroma that told me something was wrong. Don’t remember exact replacement wattage, but the wire hasn’t been above room temperature since.

You’re correct it would work but at a recovery rate so low I’m not sure that it would be usable in a house full of people.

John clarified that it’s 240 volts.

Bob, I’ve done just that. Thanks.

NJ currently follows the 2017 NEC with a few local statewide amendments. What is the HWH wattage?

You would need 10 gauge wiring and 30 amps. breakers for a 4500watt WH, however, there are lower wattage WH even some with 3 elements.

Won’t be at the property until next week to be certain — fairly sure there are 2500 watt elements in the water heater now.

For an 80 gallon tank?

If the maximum ouput is 2500 watts then a 20 amp circuit is sufficient. Typically these HWH’s have two elements that operate one at a time.

Yes. The storage capacity so exceeds use to the extent, as I understand it, that it’s never drained enough to require a fast reheat. This is in a two bedroom townhouse.

Bedminster Construction Dep’t. has informed me that I may keep existing wiring only if I install a water heater labeled for it. I either have to find a unit designed and labeled for a 20 amp circuit or install a 30 amp circuit. I appreciate the information offered here. Thanks to all.

A 3500 watt HWH can be used on a 20 amp, 240 volt circuit. 3500/240=14.6 amps*125%=18.2 amps minimum circuit ampacity.

So a 3800 watt unit should work – 3800/240=15.833 amps x 125%=19.8. AO Smith makes a 50 gallon 3800 watt unit. Rheem makes a 40 gallon 3800 watt unit. For a two-bedroom townhouse, I have to determine if either capacity will work. The Rheem appears to have ready availability, not sure about the AO Smith.

Yes, a HWH is considered a continuous load by the NEC which means to calculate the branch circuit you must add 25% to the current.

Also you can look at the inverse for a 20 amp circuit, that would be the same as multiplying 20 amps by 80%, so 20 amps*80% = 16 amps maximum.

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20 amp circuit, protected by a 20 amp breaker, or fuse, must be served by 12 AWG CU conductor.
How to figure Volts-Amps-Watts for residential water heater
Sorry for the edit.

A 20 amp circuit does not need 10 gauge wiring.