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



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.

[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....