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    buildersam's Avatar
    buildersam Posts: 1, Reputation: 1
    New Member
    		  
    #1

    Nov 6, 2010, 08:05 AM
    Can 10/2 wire with 30 apm breaker be used for 40amp tankless water heater
    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's Avatar
    donf Posts: 5,679, Reputation: 582
    Printers & Electronics Expert
    		  
    #2

    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's Avatar
    stanfortyman Posts: 5,598, Reputation: 279
    Electrical & Lighting Expert
    		  
    #3

    Nov 6, 2010, 04:04 PM
    Quote Originally Posted by buildersam View Post
    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's Avatar
    tkrussell Posts: 9,659, Reputation: 725
    Uber Member
    		  
    #4

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