AWG needed for 68.5 amp 240 vac?

Hello,
Can someone please tell me what AWG copper line is required to service a 68.5 amp 240vac tankless water heater? The manufacturer recommends an 80 amp breaker.
Thank you
Bill
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there is all kinds of type wire to choose from as distance of run and as in conduit or not and you can run it in # 6 to a # 2 by just what type wire it is and the metal the wire is made out of.
So if run in Copper wire run # 2 and you can't go wrong. the wire can be smaller if you tell the conditions like length of run , type of wire you have to use , and in conduit or out.
TURTLE
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Anywhere between #6 and #2. Depends on the temperature ratings of the conductors, and how they're installed (cable, conduit, etc).
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Doug Miller (alphageek at milmac dot com)
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Also, copper versus aluminum makes a difference. I don't have a spec sheet, but alum takes a lower number. Which is a physically larger wire.
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Christopher A. Young
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Stormin Mormon wrote:

He needs ampacity of 85A rather than 68.5 because it's a continuous resistive load. #3 Aluminum type SE cable will work if the breaker and terminals are rated for 90C. Otherwise, he needs #4 copper rated for 75C or better.
Best regards, Bob
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There are variables but generally for what you're looking to do, number 4 THWN

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Thanks everyone. I don't like my subpanel setup. It's a big mess to upgrade and a long run in an old house to try to pull new wire. I'll just replace this failing tank water heater with another tank water heater.
Regards Bill

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