So the electrical install guide for Ecosmart ECO 18 requires 2 (two) 40 amp double pole circuits. They specifically mention running two grounds too which I gather would be provided if NM cable w/ground was used.
The two concerns that I have that the install guide does not request or mention are as follows:
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One: should not there be a handle tie between the two 40 amp breakers?
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Two: If I run the 4 #8's in EMT then one insulated ground #8 would suffice, no? I do realize the EMT can be used as a ground too.
Update* Talked to tech support and they do not recommend a handle tie and one ground would be enough but they recommend two.
Best Answer
Handle-ties have two reasons:
In this case, neither instance applies, so handle ties between the 2-pole breakers are not warranted. Beware: the tripping half-breaker may not have the physical muscle to trip three additional half-breakers. So you don't do something like that without affirming the device is listed to do exactly that. Otherwise you violate the rule on using items only as listed (tested).
Using both grounds is a matter of why not, since it's already in the 8/2 cable. If it was connected via plastic conduit, that wouldn't apply.
In steel conduit, the conduit is the ground and no further grounds are required; you can run a ground of any size if you're really into belt-and-suspenders. I'm sorry, I made that sound weird. I would do that.