Originally Posted by
Paul Lawrence
Thanks for you input, Julie. Except for your drawings, that's purty much what I've been describing in my posts. I wouldn't use EMT. I would run a designated ground wire in PVC which is much easier for me to work with and just as permanent. I can even go up to 1" PVC since I'm starting from scratch.
Wiring with "a network (2H, 1N)" is exactly what I've described, but that doesn't answer the question above about limiting breaker protection to 20 amps.
A little after I retired there was a change in the code that addressed shared neutrals. Prior to that, circuit protection where there are shared neutrals (H,H,N for single phase & H,H,H,N for three phase) would be determined solely on what the network was feeding. If it fed 120v loads, the breakers would be single pole. Two pole breakers would be used only to feed loads requiring two hots (208V or 240V). And three pole breakers would only be used for loads requiring three hots.
But with this setup, there was a problem - if a single pole breaker trips, the load it's feeding could cause a backfeed through the neutral
That changed. Now any wiring networks with shared neutrals have to be protected in such a way as cause all hots in a network to trip simultaneously, thereby eliminating backfeed. But I am not up to speed on how and where that rule is to be applied. We often ran into situations where the code didn't apply. An example is dedicated devices. Say you plug a refrigerator into a garage outlet. Normally the garage has to be protected by a GFCI. But with the refrigerator, that rule didn't apply because it was a dedicated device.
If you are talking about running a network through the conduit and tapping a single hot and the neutral to feed a 120V device, that's done all the time. If you want to use that same network to ALSO feed 240v loads, well, let's just say I have never heard of any situation where that is an approved installation. But I worked in and around Chicago and the codes there are much more stringent. Even if the NEC said that's okay, I wouldn't do it. You have conduit. It's easy to pull in a dedicated 240V circuit. Since you're sharing the ground, it's only 3 wires. Why mess with success? And if you pull in #10 for that network, you're ready should you buy a machine that requires 30A protection.
That's my two cents.
“Travel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain