I called a plumber to upgrade my water heater. The current breaker is a 20A. The new water heater requires a 30A.
But my wiring is #12.
The plumber said, without much conviction, that it's fine for now, and installed the new water heater.
My current setup is:
20A breaker 240V, #12 wire, new water heater.
As soon as possible, I'll upgrade to:
30A breaker 240V, #10 wire.
What's the worst that can happen in the mean time ?
Best Answer
The standard 240V water heater only has one speed (choice of amp draw): 23A. That is how all such hot water heaters are sized. The reason is they want it as fast as possible while falling within a statutory 24A limit.
Now back to the 240V scenario.
All of the advice to follow violates Code. The only Code-correct solution is correct cable and breaker, but you knew that.
So expect a lot of breaker trips.
Wait 1 hour before resetting it. That is because of this particular situation - we know exactly why it is tripping, so the consequences of resetting it too soon are also known.
If you upgrade the cable to #10 copper (10/2 will suffice), then you can reset it as often as you please. I am assuming perhaps it is hard to obtain the right breaker due to obsolescence (PushMatic) or complexity (quadplex).
If you have a Federal Pacific, Zinsco or Challenger panel, those panels are dangerous and you are already playing with fire, so don't push your luck with those panels.
You will have fewer trips if you take great pains to use hot water VERY sparingly - follow California drought or boondocking-in-RV rules. Get wet, shut the water off, lather up, then do a quick rinse... Select cold water in dishwasher and washing machine... Let the soap do the cleaning not the heat... Etc.