First lets start with the nec code for this water heater application.
Breaker size for electric hot water tank.
Rheem tankless electric water heaters make it easy to enjoy instantaneous continuous hot water space saving design and significant energy cost savings.
The circuit wiring typically includes a 30 amp double pole breaker and 10 2 non metallic nm or mc cable.
The 20 amp size breaker is used for dedicated appliance.
Electric water heaters require a 240 volt dedicated circuit which serves only the water heater and no other appliances or devices.
Just follow the three simple steps below to choose the right model and size you need.
I agree with you that this water heater circuit is not a typical configuration and the common circuit for a new home is 10 copper wire protected by a 2pole 30amp circuit breaker however lets look at this application carefully.
Choose the right tankless electric water heater for you.
Understanding water heater wiring.
At the water heater the black circuit wire connects to the black wire lead on the water heater and the white circuit wire connects to the white wire lead on the water heater.
Now in order to choose an electric breaker multiply the current draw of the water heater with 125 per cent in order to determine the size of the breaker you will need.
But with a 25 amp breaker the 20 amp water heater will only cover 80 of the total capacity of the circuit breaker.
You can estimate the necessary tank capacity in gallons based on the number of people in the house.
Of course pairing up the right circuit breaker according to the water heater demands is useful.
1 or 2.
For example a 20 amp hot water heater needs 12 gauge wire a 25 amp hot water heater requires 10 gauge wire and a 30 to 40 amp hot water heater requires 8 gauge wire.
In the above example we would require a 15 6 amp circuit breaker for our us readers.
Multiply the current rating of the water heater with 125.
A 40a breaker would be appropriate to protect 8 wiring but it would not be preferred to protect a standard water heater at 40a.
The installation instructions for the heater may should list the required breaker size.
The 15 amp size breaker is used in general circuit wiring.
In north america the standard sizes for breakers are 15 20 30 and 40 amps.
Some large heaters draw up to 50 amps requiring 6 gauge wire.