Wiring with 240 VAC / 120 VAC At Every Outlet

[phil harold]

I have the same ones in my shop!
very handy

Its completely code compliant as long as a two pole breaker is used;https://www.leviton.com/en/products/5842-I

[Paul F Franklin]

If you have multiple receptacles on a 20 amp protected circuit they are allowed to be a mix of 15 and 20 amp rated devices (or all 15 or all 20). Note that a duplex receptacle (most common type) is considered two receptacles so you can have a single 15 amp rated duplex receptacle on a 20 amp circuit. By code, you can not have a single (not a duplex) 15 amp receptacle as the only device on 20 amp circuit. As a practical matter, most inspectors wouldn't flag this odd case, but why bother? Just install a duplex receptacle and there would be no issue.

[Paul F Franklin]

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.

It does no harm until you disconnect the shared neutral believing the circuit to be dead only to find it is very much hot because only one of the two breakers was shut off. There is no simple way (short of a current probe) to determine this is the case until *after* you disconnect the neutral, often getting shocked or showered in sparks in the process. This is because the neutral will be at ground potential until you disconnect it, whereupon it rises to 120 volts because it is back fed by the other breaker. So the requirement that a 2 pole breaker (or two singles with handles tied) be used to protect MWB circuits is really a safety issue.

[Thomas Crawford]

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.

The way I've read the installation it appears it would preclude you from ever having a 30 amp circuit unless you disconnected all the 120 volt receptacles on that shared breaker.

Edit: specifically if you were using this: https://www.leviton.com/en/products/5842-I

[Paul Lawrence]

I'm purty serious about wiring my little shop with 10AWG stranded wire. The cost isn't enough different to matter to me in the initial job. For instance, here's a list from Lowes online store:

100 ft. spool 12AWG any color $27

100 ft. spool 12AWG any color $34

Note: Solid wire of the same AWG is a few dollars cheaper per 100 ft. roll.

It just seems to make sense to completely wire the shop with 10AWG 3-wire network (plus ground) with drops for 20 amp / 120 VAC duplex receptacles ("Red is Right!" )

• 10AWG wire handles 30 amp / 240 VAC ("breaker is for the wire; not the load")
• 20 amp 240 VAC breaker per branch with bound toggles for safety
• PVC 1 inch drops every eight feet terminated with dual duplex 20 amp / 120 VAC receptacles
• PVC 1 inch main conduit for distribution and expansion
• 30 amp / 240 VAC circuits just for big air compressor and DC

If I need 240 VAC at a drop, then I don't have to run more wire (unless the load requires it). Just replace the duplex receptacles (or add another box/receptacle.)

All of this is even more flexible if you consider the PVC drops are on the surface and moveable / removable.

[David L Morse]

• 10AWG wire handles 30 amp / 240 VAC ("breaker is for the wire; not the load")
• 30 amp 240 VAC breaker per branch with bound toggles for safety
• PVC 1 inch drops every eight feet terminated with dual duplex 20 amp / 120 VAC receptacles
• PVC 1 inch main conduit for distribution and expansion
• 30 amp / 240 VAC circuit just for big air compressor and DC

You can't use 20A receptacles on a 30A circuit.

[Paul Lawrence]

You can't use 20A receptacles on a 30A circuit.

Of course. Sorry I got carried away by the bogey man there for a bit. Corrected the original post.

[Robert Engel]

If I remember correctly in 2017 code there was a change about sharing neutrals.....I think it was changed to not allow it unless the breakers for the hots are linked together......

Don't know about the linked breakers, but my electrician told me 1 neutral can be shared by no more than 2 circuits.

One option I really wish I had done is to run 2 hots in the conduit and go to split each outlet, or bypass one and have alternate outlets on separate circuits.

Here's why this can be an advantage: if you're collecting a miter saw with a shop vac on the same circuit, it may cause an overload when you start up the saw.

[Julie Moriarty]

I'm purty serious about wiring my little shop with 10AWG stranded wire.

When I'm laying out a job I like to make it so each successive step is easier. Installing conduit and boxes in such a way as to make the wire pulling easier - eg: minimizing bends where possible, locating boxes only where needed, installing larger than called for boxes - deep boxes replacing standard depth ones, etc. Pull the wire in such a way as to make the terminations easier - pulling wire that won't be tapped in a box through the boxes to eliminate splices and free up space in the box.

But in a workshop, it's important to plan ahead, too, more so than in a typical residential or commercial installation. So you may install additional boxes in locations that allow you to tap into them later. You may want to upsize the conduit so you can pull in additional wiring later. You may choose to put splices or loops in every box (excluding travellers for 3&4 way switches) so you can more easily access them in the future. Flexibility is king in laying out the electrical in a workshop.

In my workshops, I installed 3&4 way switches around the shop to operate the DC; two duplex receptacles at every wall box - one on circuit A, the other on circuit B; deep 1900 boxes anywhere 3 conduits enter the box; 11B (4-9/16" square) where 4 enter the box. I like a lot of room for splicing and accessing later should I want to pull in additional wiring.

As to upsizing wire, I do that only where I think I may need larger wire in the future. Unless you have long wire runs, there is no need to pull in #10 to feed 20A receptacles you know you will never change. There really is no benefit. If you are loading the breakers to no more than 80% of rating, #12 THHN is good all day long on a 20A breaker. There's nothing wrong with pulling in #10 but it will make pulling and splicing a little harder and will leave less room in the conduit and boxes for future expansion.

And you'll have to add some grey and blue wire nuts to your shopping list.

[Julie Moriarty]

... my electrician told me 1 neutral can be shared by no more than 2 circuits.

For single phase systems, this is true. For three phase systems, three circuits can share one neutral.

[Jim Becker]

Julie, I agree with your method of planning and implementing things. I wish I would have done "more" of that while initially setting up my shop, but that was a long time ago in a (mental) galaxy far away. The most recent electrical work I've done in my shop was more in line with what you describe, such as the setup for the CNC and the MiniSplit.

[Julie Moriarty]

Julie, I agree with your method of planning and implementing things. I wish I would have done "more" of that while initially setting up my shop, but that was a long time ago in a (mental) galaxy far away. The most recent electrical work I've done in my shop was more in line with what you describe, such as the setup for the CNC and the MiniSplit.

Oh, but the work we could have saved ourselves if our crystal ball worked better.

Wish I could stay and chat but I have some ductwork I have to tear out and replace.

[Ryan Mooney]

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.

The neutral carries the imbalance between the two (or three in 3phase) hot circuits. So in theory you can loose the neutral and as long as the loads are balanced everything is "fine".. until its not.. in which case the current imbalance will cause one leg to brown out and the other to surge. This is effectively the same problem as if you have a loose neutral on the mains supply (the so called "floating neutral") which is a fun way to start a fire. On a smaller branch circuit with oversized wire.. idk how to reasonably reason about the risk, its assuredly lower.

[Matt Marsh]

It does no harm until you disconnect the shared neutral believing the circuit to be dead only to find it is very much hot because only one of the two breakers was shut off. There is no simple way (short of a current probe) to determine this is the case until *after* you disconnect the neutral, often getting shocked or showered in sparks in the process. This is because the neutral will be at ground potential until you disconnect it, whereupon it rises to 120 volts because it is back fed by the other breaker. So the requirement that a 2 pole breaker (or two singles with handles tied) be used to protect MWB circuits is really a safety issue.

This is one of the main reasons the code was changed, mandating that all ungrounded conductors be tied to a common trip breaker. This, and a common trip breaker, assures that each leg of the multi-wire branch circuit are on different legs. As mentioned earlier, the neutral only carries the imbalance of the current. This is why when applying adjustment factors, the shared neutral does not have to be counted as a current-carrying conductor, whereas in individual branch circuits, the neutral always has to be counted.

[Paul Lawrence]

Jason Roehl, summed up a lot of what I've been working out from this whole discussion in his post quoted below.

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.

And I'm not discounting what Julie Moriarty has stated in her post partially quoted below. My response is that I don't know which box will need to turn into a 240 VAC outlet. (I'm starting with my old equipment with upgrading in mind.) If I run the 10AWG now, the changeover will be quick later. And Jason mentions "sistering" an additional box/outlet as a way to expand, too. And, remember, that there isn't that much difference in cost between #12 and #10.

... As to upsizing wire, I do that only where I think I may need larger wire in the future. Unless you have long wire runs, there is no need to pull in #10 to feed 20A receptacles you know you will never change. There really is no benefit.

PS. I'm sure a lot of you are starting to think, "You're over-thinking this project!!!" That's true, but it won't stop raining! The dozer is waiting to lay down the gravel.