Backstory: I'm considering replacing my current tank water heater with a tankless whole-house unit. The units I see generally require a 120-amp breaker circuit.
Currently, my panel has two ganged switches marked "50" supplying the water heater. My understanding was that the two breakers, each calibrated for 50 amps, are wired in parallel to produce a 100-amp circuit to the water heater. So, I probably need to have an electrician swap out that breaker for a slightly beefier one (and make sure the installed wiring can handle the extra power) as part of the upgrade.
But, when looking thrrough the electrical section, I saw ganged circuit breakers numbered with "60" on each switch labelled as a "60-amp breaker". This would imply to a relative layman like myself that the entire package will trip at 60 amps of draw. If that's true, I may need a second input panel just for the tankless, 'cause the full panel for my house is only rated 200A, which seems to be the average for a single-family home when looking at breaker boxes in that same aisle.
Can anyone unconfuse me here?
Best Answer
A double-pole breaker with a "60" on each half will trip at 60 amps. The reason it's two connected breakers is to give the circuit 240V potential, by using two opposing AC phases. These do not "add up" to more current -- you're using them to double the voltage.
So if the heater requires 240V power at 120amps, you will need double-pole breakers that can provide a total of 120amps, e.g. 4 30A double-pole breakers as Tester101 suggested.
An electrician will be able to tell you if your service panel can accommodate this extra load -- it's a lot, but your 200A service might be adequate, depending on the normal load elsewhere in your home.