I am installing a new electric point-of-presence hot water heater which requires 3 240v 50 amp circuits (6 hot wires, 1 earth ground). The water heater is roughly 50' from my panel.
I would like to run the wires from my main panel in PVC conduit (the grey sched 40 stuff the big box stores sell) to make a neater installation, rather than attempting to run three 6/2 cables (not to mention there is only 1 connection point inside the water heater for an earth ground, so running three 6/2 cables, each with its own ground wire, would be problematic as to what to do w/ the other two ground wires in the cables.)
I've read through the NEC to attempt to ensure I will be compliant, but I am still unsure as some of the language is confusing...
I read I can run #8 (rather than #6) THWN/THHN for a 50 amp circuit when the THWN/THHN is installed in conduit "as part of a 3-wire set". I am unclear as to what exactly is meant by that... e.g. when they say "3 wire set" do they mean something like 6/3 where you have two hots and a neutral and ground wire, or is 6/2 a "3 wire set"?
Is it permissible under the NEC for me to run all 6 hots plus one earth ground in the same conduit (in which case, from what I see, I can use 1" conduit), or do I have to have a separate conduit run for each "3 wire set"? The conduit fill tables seem to indicate it is permissible, but then I ran into that "3 wire set" language elsewhere which confuzzled me.
I know it is not permissible for me to run NM cable through conduit and do not plan to do so.