Water Heater minimum circuit is??

Is a water heater considered to be rated continuous duty and subject to 125% rating?


Yes, if it is 120 gallons or less, it is considered continuous duty and the water heater amps must not exceed 80% of the circuit conductor rating.
(This is the same thing as 1.25 times the amps just said in a different way)

An exception exists if you use a circuit breaker rated for continuous operation at 100% of its rating but these may not be readily available items.

This was found via google and not direct from a code book but I doubt if this has changed any lately.

Thanks Bruce,

That is what I thought.

That’s why a typical 50 gallon heater has (2) 4500 watt elements that don’t operate simultaneously - keeps the current well within the 80% limit for a 30 amp breaker.

This was a 30 gallon with if I recall correctly, was something lower, like 4300/3800 + or - some change. It was on a 20 amp breaker and wired with 12 wire.

Seems like it has a potential to be a higher demand than a 50 gallon unit.

It’s pretty important you know the KW rating before you go and write it up as being under sized. You say it might be 3.8KW, which would make it ok on a 20A ckt.

I guess higher ‘water’ demand would not be an issue if we consider the unit to be continuous duty anyway. However, while 4300 watt elements would exceed 80% of a 20 amp circuit, 3800 would not. As a home inspector, I probably would not write up either if it appeared that the system had been operating ok for a lengthy period of time. In all this I am assuming the circuit ws a 20 Amp 240 volt circuit.

The actual rating was 4500/3380. While what you say is correct for some instances, if an element is energized drawing anything over 4000 watts it exceeds the 20 amp continuous duty rating.

I put in the report that is was undersized and advised it be wired to a proper amp circuit. I may have verbally advised something realistic when they replaced the undersized and aged water heater that exhibited signs of previous leakage.

You need to account for each element which are both over 4000 watts at 240VAC, exceeding the 20A rating. The rating was actually 4500/3380.

Why worry if it is not popping?

What’s realistic and what is “right” may be two different things at times.:mrgreen:

William, the two KW ratings are for 240 volts and 208 volts, not for one or two elements. At 240 volts, your water heater uses 4500 watts, one element at a time. If both elements energized (which would be a malfunction), it would use 9000 watts.

The thermostat relay is designed so that it can only energize one element at a time, when it makes at one, it breaks at the other.

Thanks Brain…I had a “duhhhh” moment there. I blame this terrible cold I have and the medication side effects. :roll:

Anyway, what I was really trying to say was that when an element is energized, it would be drawing current in excess of the 125% rating if were rated at anything above 4,000 watts.

I really don’t know what I was thinking after that. (Medicine head)

I think I adjusted my previous erroneous BS Brian.