Water Heater minimum circuit is??

Specific Inspection Topics Electrical Inspections
1

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

Thanks,
Bill

2

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.

3

Thanks Bruce,

That is what I thought.

4

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.

5

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.

6

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.
(3800/240=15.83Ax1.25=19.79A)

7

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.

8

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.

9

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.

10

Why worry if it is not popping?

11

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

12

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.

13

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.

Bill