20 amp breaker for water heater

20 amp breaker, with 10 gauge wire, installed on 50 gal. Whirlpool heater (upper left breaker).


Thanks in advance.


Probably too small but what is the heater wattage?

I’m assuming 4500, no? Isn’t that typical for newer, 50 g electric? Not 100% sure, though.

If it’s 4500 then the 20 amp will work but it won’t be code compliant. A water heater of this type is required to be considered a continuous load meaning that the branch circuit needs to be calculated at 125% of the heater’s rated ampacity.

4500/240 = 18.75 amps, will work on a 20 amp OCPD but,
18.75*125% = 23.4 amps, requires a 25 or 30 amp circuit.

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Great information Robert, thanks.

Here’s a good link, I like it anyway.

How to figure Volts-Amps-Watts for residential water heater

You’re welcome, here’s a few NEC sections to accompany my last post:

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My 40 gallon has been on a two pole 20 for more than 5 years with no problem.

Great link !

I know this is old thread, but I have a setup for the same example above. Except in my case the breaker in the box is 30amp everything’s good there, but that circuit is run through a reliance transfer panel that is on a 20amp breaker when set to run on the generator. It uses 10 gauge wire all around so thats fine but i’m wondering if that 20amp breaker is an issue while set to generator. It doesn’t pop when running but I just want to be sure its safe.