Wiring with 240 VAC / 120 VAC At Every Outlet

[Paul Lawrence]

#3. Run 1" conduit in a ring around the perimeter of the shop at ceiling height. Start at the panel with two stubs up to go in each direction. Every 10' install a 4&11/16" junction box. Drop down out of the JB's with 1/2" conduit to 4" boxes as needed. Use a single #10 wire to ground everything, and install wire and receptacles as needed. If you're comfortable with Edison circuits (multi wire branch circuits) you can have two 120 volt and one 240 volt outlet in each 4" box with only three conductors plus the ground. Don't overdo the circuits to start, grow into what you need.

In a different thread, John Lanciani made the above suggestion, but there wasn't much said about his suggestion. I was planning on wiring my new shop (from scratch) this way only I was going to provide potential drops every 8 feet. I am splitting up sides of the shop to limit the outlets on any one circuit to less than 10.

I can't find anything in NEC search that says I can't derive 120 VAC for my outlets from a 240 VAC drop. As long as I provide a 20 amp breaker on each leg of the 240 VAC, I should be OK. That dual 20 amp breaker would still have both sides mechanically tied together, which could be a bit of a nuisance for a 120 VAC overload; all outlets on both sides will lose power.

Its a small shop and just me working in it, so I'm sure that I won't be tripping any breakers anyway. As I add machinery, the loads will be evaluated.

I'd be interested in reasons for or against doing this surface-mount wiring setup.

[Mike Cutler]

Yes, you can do it, as long as it's allowed by code in your area.
Wouldn't it be easier to install dual voltage receptacles in each box? This would give you a single 240/20 amp, and a single 120/20amp, receptacle in the same receptacle housing at each box. Alternate poles every other box.
Install 30amp receptacles on a separate breaker.

[Jim Becker]

It's not that simple, Paul. You'd need a four wire circuit to do dual voltage properly (you need the neutral for the 120v outlets and neutral is not the same as ground) and you'd also want to be absolutely sure that you're not running both a 240 tool and a 120v "something" at the same time on the same effective circuit/breaker. This is completely separate from whether or not it's even permitted by code which I cannot provide an answer about.

Personally, I'm fine with terminating both 240v and 120v circuits in the same places, even in the same (oversize) boxes with separate outlets, but I'd personally NEVER have them on the same circuit/breaker, even if it's permitted by code. (and again, I don't know if it is or not) I do have one dual voltage circuit in my shop, but it has exactly one receptacle with an L14 four wire termination and it's for my CNC machine which requires both 120v for the controller circuitry and 240v for the VFD that powers the spindle. But that's all on one machine that's designed to require a four wire, dual voltage circuit.

Surface mount with raceway or conduit is perfectly fine. I've employed the latter quite a bit as I've made changes to my shop over time since getting into the walls would be a thankless task.

[John Lanciani]

It's not that simple, Paul. You'd need a four wire circuit to do dual voltage properly (you need the neutral for the 120v outlets and neutral is not the same as ground) and you'd also want to be absolutely sure that you're not running both a 240 tool and a 120v "something" at the same time on the same effective circuit/breaker. This is completely separate from whether or not it's even permitted by code which I cannot provide an answer about.

Personally, I'm fine with terminating both 240v and 120v circuits in the same places, even in the same (oversize) boxes with separate outlets, but I'd personally NEVER have them on the same circuit/breaker, even if it's permitted by code. (and again, I don't know if it is or not) I do have one dual voltage circuit in my shop, but it has exactly one receptacle with an L14 four wire termination and it's for my CNC machine which requires both 120v for the controller circuitry and 240v for the VFD that powers the spindle. But that's all on one machine that's designed to require a four wire, dual voltage circuit.

Surface mount with raceway or conduit is perfectly fine. I've employed the latter quite a bit as I've made changes to my shop over time since getting into the walls would be a thankless task.


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

[Mike Cutler]

Jim
It is code compliant. It just has to be done in a prescribed manner. Of course, the local codes have to allow it also.
It's easier to understand the concept when looking at a newish washer/dryer, stove/oven. In these devices the 120vac is exactly that, a tap off one of the 240 legs.
My washer has a 240/20 amp plug that plugs into the back of the dryer, which is plugged into a 240/30 amp receptacle. The 120vac, for both machines, is taken off one of the 240 legs.They probably split the poles inside each appliance to balance the load.

[Paul Lawrence]

... You'd need a four wire circuit to do dual voltage properly (you need the neutral for the 120v outlets and neutral is not the same as ground) and you'd also want to be absolutely sure that you're not running both a 240 tool and a 120v "something" at the same time on the same effective circuit/breaker....

... but I'd personally NEVER have them on the same circuit/breaker, even if it's permitted by code....

Jim, I think this would be called a 3-wire circuit with ground.

I'd be curious to hear your reasoning/objection to running a 120 and 240 load on the same circuit, as I'm sure that is done in every household. Of course, the sum of the loads would have to be considered, but I wouldn't just make an arbitrary rule.

Since I will have a plethora of outlets, I think I'll only end up terminating a particular drop with a 240 outlet. I wasn't really thinking of having dual 240/120 outlets installed.

The key would be that the wiring is already present for this option.

I can see that juggling the breaker vs. load game would be very important.

[Bill Dufour]

If you are going to run 240 volts I would want 30 amps or more. I think the 120 in a shop should be GFCI just in case.
Bill D.

[Paul Lawrence]

If you are going to run 240 volts I would want 30 amps or more. I think the 120 in a shop should be GFCI just in case.
Bill D.

... and if there's a huge drawback to this method of distributing power to various loaded outlets, it is the mixing of high-power 240 VAC outlets with maximum 20 amp 120 VAC outlets.

If you protect a 30 amp 240 VAC load with an appropriate breaker, then any 20 amp outlets on that branch will not have appropriate overload protection.

What that emphasizes is that all of the outlets on this type of distribution have to be protected with a breaker appropriate for the 20 amp 120 VAC outlets.

A 30 amp 240 VAC outlet would have to have a separate run protected by a 30 amp breaker. Something one would do anyway, and distributing in the way mentioned above would allow room for that addition in the conduit initially installed.

So, is there a disadvantage to having a somewhat limited 20 amp 240 VAC outlet? Would that be a severe limit on 240 VAC tool selection?

[Julie Moriarty]

If you are going to take the time to install conduit, why skimp on the wiring? Just pull in a network (2H, 1N) for the 120v devices and wiring for the 240v devices. Grounding isn't necessary if the conduit is metallic, such as EMT. Just make sure your fittings are snug.

As for running a conduit run at the ceiling and dropping feeds down, if keeping wall space open is the reason, by all means, do it. But you could also do something like this

http://julimorcreations.com/Images/CondBend/Conduit%20Tutorial-3D%20PLAN.png

Put the dust collector on its own circuit, install two 120v receptacles, each on a different circuit, at each box and install the 240v receptacles where you need them. That should handle pretty much any kind of tool layout you might do, now or in the future.
http://julimorcreations.com/Images/CondBend/Conduit%20Tutorial-PWR%20PLAN.png

[Mike Cutler]

... and if there's a huge drawback to this method of distributing power to various loaded outlets, it is the mixing of high-power 240 VAC outlets with maximum 20 amp 120 VAC outlets.

If you protect a 30 amp 240 VAC load with an appropriate breaker, then any 20 amp outlets on that branch will not have appropriate overload protection.

It also is not allowed by code. 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. In many houses you will see a 120/20amp breaker protecting a 15 amp duplex receptacle.

What that emphasizes is that all of the outlets on this type of distribution have to be protected with a breaker appropriate for the 20 amp 120 VAC outlets.

Once again, it's the conductors that are protected, not the receptacles.

A 30 amp 240 VAC outlet would have to have a separate run protected by a 30 amp breaker. Something one would do anyway, and distributing in the way mentioned above would allow room for that addition in the conduit initially installed.

So, is there a disadvantage to having a somewhat limited 20 amp 240 VAC outlet? Would that be a severe limit on 240 VAC tool selection?

No. My shop was run on 240/20 amp branch circuits for over 20 years. The garage sub panel was protected by a 240/30 amp breaker. I ran a 3HP planer and a 3 HP dual drum sander with a 1-1/2HP dust collector. My band saw and table saw are 2hp,a nd the second table saw and jointer are 1-1/21/2hp motors. I never tripped a breaker. The lights used to react though.
I upgraded the wiring for two reasons. First I wanted to run a 5hp air compressor. Second, I hit the improperly buried service with the corner edge of a plow one winter night.


If you are allowed to use the dual voltage receptacle I referred to in a previous post, not all places allow them, the splitting of loads would be easier. You would pull three, Black, red, white, #12awg, THHN/THWN conductors, through the conduits. Drop all three to each box. The 120vac is the top,so the white neutral conductor connect to the 120 receptacle. The black and red conductors would alternate top/bottom at each receptacle along the circuit. The end result is that every other receptacle is on the same back, or red conductor and it's respective pole. Pulling separate 240 and 120 circuits to the same box is a mess of conductors to deal with in a small space. If you try to split them that's 5 #12 conductors, + ground in one box. Add the receptacle yoke and that brings the total to 6+1, or 7. This may exceed the stuffing capacity of a smaller box.

One topic not yet covered is GFCI protection. The 120vac outlets needs to have GFCI protection. If you do multi wire branch circuits you're going to have to protect all the wiring and the easiest way to accomplish this is with a a 240vac GFCI feeder breaker.
Depending on whether or not this is an attached, or detached building may require two of these,based on local code. One in the main service panel and one in the sub panel to act as a disconnect if you exceed 6 total positions. These breakers are going to cost $75-$100 each and one of them has to be service breaker rated, if the box is a sub panel in a detached building. Whatever you save on wiring is going to get eaten up providing the GFCI protection.

Julie has provided an excellent example for small shop wiring layout! I would really lean toward heeding her advice. It will save you a lot of effort down the road if you want to modify the wiring at a later point.;)

[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.

Mike, as far as GFCI is concerned, I was under the impression that I can still use a GFCI receptacle for the first one in the whole branch circuit. My shop is a detached, portable building that will be fed direct from the main service panel 200 amp breaker to a 100 amp sub panel for the shop. I didn't have any additional requirement for GFCI when I wired my 100 amp house into this main service panel.



If you are going to take the time to install conduit, why skimp on the wiring? Just pull in a network (2H, 1N) for the 120v devices and wiring for the 240v devices. Grounding isn't necessary if the conduit is metallic, such as EMT. Just make sure your fittings are snug.

As for running a conduit run at the ceiling and dropping feeds down, if keeping wall space open is the reason, by all means, do it. But you could also do something like this ...

Put the dust collector on its own circuit, install two 120v receptacles, each on a different circuit, at each box and install the 240v receptacles where you need them. That should handle pretty much any kind of tool layout you might do, now or in the future.

[Robert Engel]

Well Julie is an electrician so I wouldn't dare comment on whether that's the way to go. ;-)


In my shop, they electrician ran multiple circuits in conduit (3-4hots, neutrals and a groud), and run other circuit wires past outlets or when appropriate, drop to JB's and branch from there.

I have 1 - 240V dedicated circuit for my 220 machines.

I don't understand why you would want to bring a 110 circuit off a double pole breaker but you would have to separate the breaker toggles, right?

Wouldn't it be more appropriate to just run individual 110 circuits? Wire isn't that expensive why not pull an extra hot or two?

[Terry Kelly]

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......

[Jim Becker]

While I'm glad to hear it's code compliant, I still would not do this personally. I just do not like the idea of mixing things like that and prefer dedicated 240v connections for machinery that requires 240v. Relative to it existing in households...that's true...dual voltage connections are common for appliances that require both 120v and 240v internally, such as a modern range, similar in setup to the CNC machine I mentioned previously, but those are almost always dedicated circuits. That said, I certainly can see the appeal of this method for someone who moves things around a lot, but honestly, there's not much added expense to have the 240v supply for machines on a separate circuit or circuits from the 120v stuff and there will never be a need to even worry about contention. But again, since it's code compliant (assuming local code enforcement concurs) there's no technical reason you can't do it if you are personally comfortable with the method.

[Terry Kelly]

I would not do this either....

[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 (http://mjobee.com/projects&news/nec%20art%20210.4.pdf) 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 (http://mjobee.com/projects&news/nec%20art%20210.4.pdf) 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
393015
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 (http://mjobee.com/projects&news/nec%20art%20210.4.pdf) 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! :D

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.

[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 (https://www.lowes.com/pd/Southwire-100-ft-12-AWG-Stranded-Green-Copper-THHN-Wire-By-the-Roll/50101624)

100 ft. spool 12AWG any color $34 (https://www.lowes.com/pd/Southwire-100-ft-10-AWG-Stranded-Black-Copper-THHN-Wire-By-the-Roll/50101602)

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!" :D)


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. :rolleyes:

[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. :D 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. :D 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. :rolleyes:

[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. :D

[Julie Moriarty]

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. :D
When you can't work, think away! Overthinking can save you a lot of work later on.

When in doubt, add a box. When in doubt, leave a loop of wire when pulling. If you pull in two networks, one with (3) #12 and one with (3) #10 and leave loops at every box where drops might be, you should be covered for anything your shop will need. Unless you start buying big commercial machines. ;)

[Van Huskey]

First, I don't want to be a downer but it seems the genesis of the thread is "future-proofing". All I can say is I wish I had all the money I spent on future proofing and never used back. I "future-proofed" the low voltage in out 2nd home 10 years ago. There is over 1,000 feet of Cat 6 with RJ45 outlets EVERYWHERE and maybe 500 feet of RG6 with outlets for 10 TV, I use absolutely none of the Cat 6 and one run of RG6 to the main satellite box and that is it. Everything is wireless now.

More apropos to a shop I am getting ready to start my 5th shop this fall, there is no way I could have come close to future proofing my earlier shops. I would have never put in 40 amp circuits (now I need multiples), I would not have dreamed I needed a separate 3ph supply up to 40 amps and the massive ampacity needed for the RPC (I ain't runnin' no 3ph machines ever).

My suggestion is run a lot of current capacity into a large service panel, then run the conduit and run the wire and circuits you need now. Adding on will be "easy" in the future but you won't tie money and time up into guessing what you may need in the future since my guess is you will most likely be wrong and be adding circuits and pulling wire anyway.

I may be the odd duck but I won't spend money of future-proofing anything now beyond the basic infrastructure (like using conduit) to make future upgrades simple.

[Paul Lawrence]

That wiring plan settles it for me. I might just have to start a workshop post. Mine would probably be #4259 on this forum, but since it will probably take me until Christmas to do it, we might have some cold weather reading material.

Thanks to everyone for the informative and experienced comments. I can't tell you how important this has been to me, since I have been trying to get this shop started for over a decade. There's always something more important to spend the money on --- like kids growing up, doctors and medicines!

Now if it will only stop raining for a week or two ...

[Jason Roehl]

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


I think this has changed since you retired. I'm currently working with an industrial/commercial electrician (he's in his late 50s), and he told me last week that his boss told him a few years ago that they could no longer share neutrals on 3-phase circuits that aren't on tied breakers. It's kind of annoying, because my whole building is wired that way from 25 years ago, but I can see how with wiring additions over time, it could become a problem as non-electricians do things "the easy way". (I'm a maintenance tech, and I'm guilty of it at times...)

[Jim Becker]

My suggestion is run a lot of current capacity into a large service panel, then run the conduit and run the wire and circuits you need now. Adding on will be "easy" in the future but you won't tie money and time up into guessing what you may need in the future since my guess is you will most likely be wrong and be adding circuits and pulling wire anyway.


I agree with this...have the available supply there and be generous in your conduit or raceway size. That makes for easy changes later WHEN and only when they are needed. Most often, for me at least, any angst with electrical changes are more about the path, rather than the "stuff".

[Rod Sheridan]

I wired my shop with a multi-wire branch circuit.

it's great, only requires one 2 pole breaker, and every 4 inch square box has a duplex 240 and 120 volt receptacle...................Rod.

[Robert Engel]

Julie,

I've dealt with quite a few electricians over the years and have never heard circuits referred to as networks.

I've always associated networks with LAN systems.

Is this a new term or are you talking about something I've missed out on?

Thx.

[Matt Marsh]

Julie,

I've dealt with quite a few electricians over the years and have never heard circuits referred to as networks.

I've always associated networks with LAN systems.

Is this a new term or are you talking about something I've missed out on?

Thx.

It's probably a regional thing Robert. I have heard the term before, but only online. Here in Northern MN/the Midwest, the slang term is "Boat" or "Full Boat".

[Julie Moriarty]

Julie,

I've dealt with quite a few electricians over the years and have never heard circuits referred to as networks.

I've always associated networks with LAN systems.

Is this a new term or are you talking about something I've missed out on?

Thx.

It's probably regional, Robert. We have names for junction boxes, like 8B & 11B, that I learned later on, maybe 50 miles away, they called them octagon or 4-11 square. But if you're ever in the Chicago area and use terms I use here, you'll be talking the local language. ;)

One time a guy from Iowa came to our local to work. When there's a knockout removed from a box, it has to be filled. We call them KO fillers. When the guy from Iowa needed one he asked me, "Y'all have any blunder plugs?" I looked at him and said, blunder plugs!?!?!" That just cracked me up.

[Terry Kelly]

Julie,

I've dealt with quite a few electricians over the years and have never heard circuits referred to as networks.

I've always associated networks with LAN systems.

Is this a new term or are you talking about something I've missed out on?

Thx.


I use that term as well something I was taught as an apprentice.....have worked with several JW’s from around the country and they have used it too.....single phase system 2 hots and a neutral or 3 phase system 3 hots and a neutral are commonly called a network......today it’s still the same but Some don’t share neutrals....I prefer not to.....

[Matt Marsh]

Where multi-wire branch circuits really shine is when you install several circuits in the same conduit. e.g. When using #12 THWN wire with individual branch circuits in the same raceway, you are limited to 4 circuits before you have to up-size to #10s, or drop to a 15 amp breaker (50% de-rate). With multi-wire branch circuits, you can install eight single phase 120 volt circuits, and nine 3-phase 120 volt circuits, and still use 20 amp breakers.