About to order a 10hp phase perfect. Wanted to know if I can split of my 100 amp sub panel. Max load will be 7.5hp lathe. Lights are wired to the main. Can't see why not but maybe I'm missing something?
I'm not sure what you're asking. "Split"? Do you men you want to power this from a sub panel? You could... If I go with a previous reply (and I don't doubt) that it calls out an 80 amp breaker, then yes, you could install it there. 80 amps, and whatever conductor (wire) gauge that will hold 80 amps over however long the circuit is. The circuit out would be of whatever gauge is required for that rated current and circuit length. If you want to breaker or fuse it lower for a smaller load, that would be done at the wall where it plugs in or is hard wired in. Especially if you are going to use a plug (Not recommended here...), it allows you to use the appropriate plug, so that the machine will ONLY plug into the correct power, and ONLY correct machines would plug into that plug. At the point where you leave the wall, AFTER the lower rated fuses/breaker, you can drop the wire size to what that last, lower rated device can supply.
80 amps puts a heckuva dent in a 100 amp panel, but in practice, you won't often be fully utilizing it. That circuit takes away from the panel's capacity what you're using at the time, not what it says on the breaker.
In another post you asked about wires. In a workshop environment, I'm a big fan of pulling wires through conduit. Pick one kind that you can work with easily, and go with it. Go (reasonably) oversized, and do study some tables as to how many wires is "full" (you can't make a conduit physically full), and any derating that's required. (They're easy tables, all over the internet). Then stab at what size you might grow into. Then stuff it with THHN. You could use others, but that's the defacto standard for any time you don't need something else, so it comes easier. And after you leave the wall. presuming it's a short run, about any SOXXX. is fine, and there's a thousand permutations of that. I'm not sure if you said what voltage the lathe runs at, but you probably could use an SJOXXX in the same permutations as the SO, but limited to 300 volts, and WAY easier to work with.
What nec are you running from? Haven't ran across that one.
I don't think NEC cares, so long as the protection is good for every step of the way. I've seen similar, although I don't recall the percentages. it's a local code added to whatever version of the NEC they currently base their codes on. It (helps to) prevent you from making an electrical system that no other homeowner or business owner/employee could possibly understand what they can use when, and no hired electrician could possibly understand without entirely reverse engineering the entire thing from beginning to end. I suspect it probably helps towards that end. But as you say, I don't believe NEC addresses that.
