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View Full Version : Can 10/2 wire with 30 apm breaker be used for 40amp tankless water heater


buildersam
Nov 6, 2010, 08:05 AM
Just got an electric tankless water heater. It's rated at 40 amps requiring 8 gauge wire. Can I use the existing 10/2 30amp circuit for this installation?

donf
Nov 6, 2010, 11:21 AM
Absolutely not!

10/2 is not listed for 40 amps. It is listed for 30 amps.

If you put a 40 amp breaker on a 30 amp conductor, then please put your local fire department on a retainer. You will be calling them soon. For 40 amp, you are required to use a #8 (stranded) cable.

Is there any requirement for the heater to use 120VAC? If there is, then you must use a 8/3 cable instead of an 8/2.

stanfortyman
Nov 6, 2010, 04:04 PM
Just got an electric tankless water heater. It's rated at 40 amps requiring 8 gauge wire. Can I use the existing 10/2 30amp circuit for this installation?Isn't this question self-answering??

tkrussell
Nov 7, 2010, 04:44 AM
Good catch Stan.