Wiring with 240 VAC / 120 VAC At Every Outlet

[Julie Moriarty]

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.

[David L Morse]

The term used by the NEC for what the OP is describing is "Muliwire Branch Circuit. The requirements are covered in Section 210.4.

This link quotes and comments on that section and includes some informative drawings.

Julie & Terry: I think the change you're referring to happened in 2008. Most municipalities are a few editions behind the current NEC and so it was likely several years later that you saw it implemented in the field.

[Terry Kelly]

The term used by the NEC for what the OP is describing is "Muliwire Branch Circuit. The requirements are covered in Section 210.4.

This link quotes and comments on that section and includes some informative drawings.

Julie & Terry: I think the change you're referring to happened in 2008. Most municipalities are a few editions behind the current NEC and so it was likely several years later that you saw it implemented in the field.

2017 Code Change.....

[David L Morse]

2017 Code Change.....

From 2011
2011 210.4 MWB.JPG
Unfortunately I don't have 2008 on file.

[Terry Kelly]

Looked back.....2008....I should have looked further back before ptuuing that year up

[Julie Moriarty]

The term used by the NEC for what the OP is describing is "Muliwire Branch Circuit. The requirements are covered in Section 210.4.

This link quotes and comments on that section and includes some informative drawings.

I noticed your link was from a Mike Holt version. I've encouraged those asking electrical questions here to go to his website. They will always get the right answer, that is, after the local inspector. You'll never go wrong asking your inspector.

[Bruce Wrenn]

I have Multi Wire Branch circuits in my shop. Because I don't have to have GFCI, except for outlets on the wall with the door, mine is a little different. I ran 3/4" EMT, using it for the ground. At each location, I have two 120 outlets, and a single 240, all 20 amp. The circuit hits the two 120's first, and drops down to another box that contains the 240 outlet. In each box, the hot on the left passes through a sensor in the panel box that controls the DC. Anything plugged into left outlet, or the 240 outlet will control the DC. As far back as I can find, the code has ALWAYS required that the two pole breaker have a tie bar, so that both sides disconnect at the same time. As those saying a multi wire branch circuit isn't safe, take a minute and look at the service coming into your house from transformer. It's the same, two hots, with a shared neutral, and a ground, AKA multi wire circuit. Popular Woodworking had an excellent article on this several years back. As with any wiring, consult with your local inspector. He has a magic pen that can determine whether you get power.

[Josh Kocher]

I run 20 amp multiwire branch circuits in my shop.

20 amp 110V & 220V receptacles at every station.
It was half as much work to wire in, cheaper, convenient, uses less space in my box and is code compliant. Why wouldn't you? And, yes you can use both the 110 & 220 at the same time.

One additional comment - You should not be running 20 amp receptacles on a 30 amp breaker. I doubt it's code compliant anywhere.

[Thomas Crawford]

Do it "right" - which in a workshop context to me means planning for future changes and flexibility. Run 12awg for your 20A 120 and 10awg for 240 (up to 30A). Doing this combined stuff is just begging for you to regret it.

[Paul Lawrence]

Mike Cutler wrote: What's being relied upon in a multi branch circuit is that the protection of any sized conductor is not exceeded. You can put a 20 amp receptacle on a 30 amp breaker, but the wire needs to be 10awg, and that's a big wire for a duplex receptacle. The code isn't protecting the device, it's protecting the conductor.

I didn't miss your explanation, Mike, just forgot to comment. Thanks for the solid reminder. I was thinking that I have put #10 stranded wire into a duplex receptacle, but memory has failed me before.

All comments above are very informative. I think I'll plan to run a dedicated 240 VAC #10 circuit for a bigger air compressor, but I'm certain the 20 amp wiring and breakers will be fine for my shop as I see it for awhile.

I'm doing it this way because I do need wall space. My goal is to have nothing on the floor that isn't a machine!

EDIT: I looked up a couple of 20 amp duplex receptacles, and yes they do take #10 wire.

[Paul Lawrence]

Do it "right" - which in a workshop context to me means planning for future changes and flexibility. Run 12awg for your 20A 120 and 10awg for 240 (up to 30A). Doing this combined stuff is just begging for you to regret it.

Pardon me saying it, but I'm not sure you understand.

What if the wiring was all done with 10awg wiring? Wouldn't that be "planning for future changes and flexibility?"

The whole point of bringing this out in the open is to invite discussion. Just saying that somehow there will be "regrets" is not much of an explanation. What could there be to regret if the wiring for a change is already present in the conduit? At most I would have to add the proper receptacle.

[Julie Moriarty]

One additional comment - You should not be running 20 amp receptacles on a 30 amp breaker. I doubt it's code compliant anywhere.

You wouldn't believe how many inspectors have approved installations where a 15A rated device is on a circuit protected by a 20A breaker.

Paul, if you ran #10 throughout your shop and tapped into that for receptacle drops, you'll be fine. But consider how many WW power tools running on 120V would actually need 30A load protection. They may be out there but they are rare. But however you plan to wire your shop, when you're figuring breaker loads, keep them no more than 80% of the rating of the breaker. So 15A breaker loads should not exceed 12A, 20A not more than 16A and so on. Dedicated device breakers should follow manufacturer's recommendations.

[Jason Roehl]

If you're running 1" conduit, I wouldn't worry so much about the future. Pulling wire is pretty easy, and 1" conduit holds quite a few circuits.

I'd run the 10 AWG 3-wire (2H, N + G) all the way around the ceiling loop on a 240V/30A (2-pole) breaker, and either cut it and nut it in each box, or leave a service loop.

Then to save a little space, run a multiwire branch circuit with 12 AWG 3-wire (2H, N, use the other ground) on a 240V/20A (2-pole) breaker. Drop the 20A circuit (2H, N + G) into each box (I'd use 3/4" on this instead of 1/2"), and install 2 duplex receptacles, one on each hot leg.

Be consistent--left receptacle on the black wire, right on red. If you need a 240V receptacle, sister another box and use the same drop to bring the 30A circuit down, or just skip the 120V receps in that location altogether and only use one box.

[Bill Dufour]

They do make four pole single phase outlets so you can have either 120 or 240 from the same outlet. Probably cheaper to buy the extra wire then the high cost outlets and change every 120 cord end. Probably $30 each
Bill D.

http://www.generatorsforhomeuse.us/l14-30/

[Wade Lippman]

You wouldn't believe how many inspectors have approved installations where a 15A rated device is on a circuit protected by a 20A breaker.

20 years ago I was taught that it was fine to put 15a outlets on 20a circuits. They are exactly the same except for the slots; and there is no harm to undersizing the slots. Was that wrong, or has it changed? Seems safe enough to me.

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

Doesn't current always come back over the neutral on a multiwire circuit? How is this different? Since the neutral is grounded, carelessly assuming it is dead does no harm.