New Workshop Electrical Question

[Matt Przybylski]

Sam, do you happen to have a picture of how your 220 and 110 boxes sit next to each other? What I'm having a hard time with is how the conduit is run for that. Is it just all run through one 3/4" pipe to the first box, then a very short length of pipe to the next box that holds the 220, and then on to the next set of boxes down the line? in essence if the 110 box were first and the 220 second, you'd just be pushing the 220 wires through the 110 box in the back and vice versa for the 220 on the right?

[Steve Mathews]

Sam, do you happen to have a picture of how your 220 and 110 boxes sit next to each other? What I'm having a hard time with is how the conduit is run for that. Is it just all run through one 3/4" pipe to the first box, then a very short length of pipe to the next box that holds the 220, and then on to the next set of boxes down the line? in essence if the 110 box were first and the 220 second, you'd just be pushing the 220 wires through the 110 box in the back and vice versa for the 220 on the right?

I don't like the looks of double boxes but I think there are advantages based on my prior reading. Please confirm but I think pass through wires do not count in fill calculations.

[Ryan Mooney]

When it comes to grounding the boxes, receptacles, and the two circuits, you can tie all those grounds together. Get bigger wire nuts if need be, and use a small pigtail with a crimp-on ring (or forked) terminal to screw it to the box.

To clarify, if you do that you want only ONE ground return. What you do NOT want is any loops in the ground circuit. That is don't run two grounds from the panel and pigtail them together (I know Jason knows this but the details are well.. the details... which is where the devil lays in wait).
https://en.wikipedia.org/wiki/Ground_loop_(electricity)

[Art Mann]

I hope the color code you have chosen for your illustration is just a little misleading rather than bad wrong. It appears that you are using grey to depict 120VAC in the 240VAC circuit and to represent neutral in the 130VAC circuit. Yes?

[Matt Przybylski]

Art, that is correct, if you look closely you will see that I've marked the gray (what will actually be a white wire in "real life") with "black tape" to denote that it is hot, as I understand is common to do in this case.

[Art Mann]

I don't see anything wrong with your plan. In fact, that is the way I have my shop wired. There is nothing wrong with running multiple 240VAC outlets from one circuit. I did a couple of 240VAC multi outlet circuits that way and I never encountered a problem. My opinion is that running two machines at once is a safety hazard even if the two machines are on different circuits (unless you have multiple operators). If you are running a 240VAC dust collection system or a big compressor, I would provide individual circuits for them.

[Matt Przybylski]

Thanks Art, those are my thoughts on the subject as well.

[Sam Layton]

Hi Matt,

I used romex, and all of the wires are in the wall. If you are using conduit, and running it on the outside of the wall, I think you can just run the wires through the box. Here is the way I would do it if I was using conduit on the outside of the walls (check code first). Run the 120 and 220 circuits totally independent of one another even though they are in the same conduit. From the panel run 2 hots and 1 ground for the 220. For the 120, I would run 1 hot, 1 natural, and 1 ground, ( One ground may do it for both, I'm not sure). The problem with running everything in one conduit is keeping track of what wire is for what circuit. Color coding will be important. If you run two ground wires, you can not tie them together, like Ryan said. If you run two ground wires, they each only connect at the panel.

I would separate the two boxes by a few inches of conduit. I like double boxes. It clearly identifies your 220, and 120, it also gives you more room to wire things. 10 gauge is hard to work with. I ran all of my 220 with 10 gauge wire. I used 20 and 30 amp breakers depending on what size circuit I wanted. Doing it this way, it allows me to upgrade a 20 amp circuit by just changing a breaker to 30 amp.

I like using twist lock receptacles for the 220. Without the twist locks, and having both 220 and 120 in the same box, someone may try to use the 220 to plug a 120 tool into, you never know...

Today I will take a photo and post it tonight.

Sam

[Matt Przybylski]

Great Sam, thank you!

[roger wiegand]

I've never seen a 240 v outlet that would accept a 120v plug, nor vice versa, I don't think that's an issue, at least if the correct plugs/outlets are employed.

I've wired my shop so that things that can run at the same time as my tools have dedicated circuits-- these would primarily be the air conditioner, dust collector, and air compressor.

I like the convenience of multiwire branch circuits to give me two separate 120 v circuits as well as 240 in a single box with one 12-3 wire. In most boxes I put one 240 outlet and one duplex 120, splitting the 120 so that each side of the duplex is independent. That way I can plug a high draw tool and shop vac in at the same duplex outlet without overloading anything.

[Brice Rogers]

The rule for most residential wiring is that each device has to be within 6 feet of a receptacle. That means that the spacing between receptacles must be 12 feet or less. When I wired my workshop, I put in quad receptacles roughly ever six feet. I have never been sorry. Having only a duplex (2) receptacle wouldn't work for me.

While it appears permitted to include a 240 volt receptacle in the same box as a 120 volt circuit, I think that most people do not do that. Perhaps it has to do with the difficulty of pulling six wires through the conduit. You will find that when you have a lot of wires in the same conduit, it can be a little hard pulling the wires, even with pulling lubricant.

I presume that you are planning on using the gray PVC conduit? I would advise going with the larger sized conduit that your boxes will support. When you start pulling wires, you'll understand why. There is code for the max number of 90's allowed on a conduit run without incorporating a pull box.

So, if this was my workshop I would run the 240 runs in one conduit and the 120 run in another set of conduits. Also, I would use quad 120 receptacles (that is, two duplex receptacles in a single box).

[Chris Padilla]

I used the large 4 11/16 x 4 11/16 boxes and used stranded #10 for everything. I put flex conduit in the walls so I could change things later if I desired. I also Edison-wired (multi-wired) all my 120V/20A using black, red, and 1 white neutral for the return. All my 240V is 30 A and twist-lok and on their own breaker. I also ran dedicated for the dust collector and air compressor.

[Art Mann]

I believe Sam meant to say that the neutral wires from different circuits should not be tied together. The reason is the neutral wire is a current carrying conductor. It has to have a certain capacity independent of any other circuit. You have more freedom with the ground wire because it never carries current unless the circuit is faulted out. If that happens, one hopes the breaker will open the circuit.

Great Sam, thank you!

[Chris Padilla]

I put in quad receptacles roughly ever six feet. I have never been sorry. Having only a duplex (2) receptacle wouldn't work for me.

I believe they use the term single and double-gang to refer to number of receptacles in a box. So your quad would be considered a double-gang and the duplex a single-gang.

[Chris Padilla]

I believe Sam meant to say that the neutral wires from different circuits should not be tied together. The reason is the neutral wire is a current carrying conductor. It has to have a certain capacity independent of any other circuit.

And I think you are saying: In its most basic form, the neutral will need to at least carry the same amount of current as the hot wire in a circuit. In the case of a multi-wire or Edison-wire style, it can carry less if both the red and black hot are drawing. So in a nutshell, each circuit needs its own neutral...except in the multi-wire or Edison-wire style which only needs one neutral despite being two circuits (I think it is appropriate to call such a wiring style as having two circuits?).

You have more freedom with the ground wire because it never carries current unless the circuit is faulted out. If that happens, one hopes the breaker will open the circuit.

Actually, the ground can carry current just fine and never trip the circuit breaker. It is there mostly to keep the current flowing back to the panel and not through a person who might touch metal that is accidentally being used to carry current. Now if that circuit has a GFCI on it (receptacle or breaker), THEN the GFCI will trip in this situation since it will detect a large current difference between the hot and neutral (since the white neutral is no longer the return path back to the panel for the current).