Shop Electrical question

[Steve Roxberg]

I am going to rewire a large portion of my shop and have some questions.

My shop is in the basement and the subpanel is in the same room. The existing outlets are wired by running romex along the floor joists and then down into conduit to the actual wall boxes.

I am planning on running conduit horizonitally around the room about about 54" high and having boxes about every four feet.

Can or should I run two seperate 20amp circuits through the conduit so I can alternate which circuit is being loaded. Meaning I would alternate every other outlet to a different ciruit so that a vacuum and a drill plugged into two seperate outlets would be on different circuits?


If I run two seperate 20amp circuits Can I share the neutral or ground and run two hots? Or would I needt to run two hots, two neutrals, and two grounds?

Should I run 1/2" or 3"4 conduit?

[Jim Becker]

You can run conductors for more than one circuit in a single conduit as long as it's sized appropriately. I can't answer the sharing question with any respect to code, but personally, I wouldn't.

[Jason Beam]

Whether or not you should is up to you and your needs. I like the idea, myself. And I think 12/3 is perfect for what you want to do. I'm unaware of any codes that require you to run all new romex for each circuit.

[Eric Haycraft]

I can't answer if using 12/3 meets code or not, but it will work. The two hots must be 180 degrees opposite of each other, otherwise you can easily fry the common wire..start a fire, etc. From a safety standpoint, you may want to stick with multiple wires..much easier to identify what is connected to what breaker and if someone accidentally moves a breaker in the box you don't risk a fire.

What I did was to have the top outlet on one breaker and the bottom outlet on another breaker and marked the outlet plates with marker to show what was on what breaker. That way I could have two large machines in the same outlet running at the same time. If you do that, you need to break away the metal tab on the hot side of the outlet. Again, I can't say if this meets code or not.

In general, the larger the conduit the better..especially if you plan on pulling more than 1 romex through. You may want to go with 1 inch which would let you pull much larger wire if you needed to add some larger wire for big 220 machines.

[Scott Velie]

You can share the ground but not the neutral. (unless the wire size is twice as large).

Scott

[Rob Russell]

Steve,

You don't say whether this is a finished or unfinished basement, but because you have access to the floor joists I'm going to interpret that as being an unfinished basement.

Based on that assumption, your receptacles must be GFI-protected (per NEC 210.8). You can't have a multiwire circuit and GFI-protect the separate parts of the circuit.

It's fine to run multiple 20 amp circuits in the same raceway (conduit). Pull (5) #12 THHN/THWN conductors for the (2) hots, (2) neutrals and 1 equipment grounding conductor. Because these are separate circuits, you can make the first receptacle on each circuit a GFI and use the "feed-through" option to protect the receptacles that are down-circuit from there.

Rob
(Addy protocol: unlicensed, homeowner electrician)

[Wade Lippman]

Steve,

Based on that assumption, your receptacles must be GFI-protected (per NEC 210.8). You can't have a multiwire circuit and GFI-protect the separate parts of the circuit.

Of course you can; you just have to use a GFCI outlet everytime, rather than one for the circuit.
If you are saying it is a bad idea I agree, but it is possible.

[Rob Russell]

Of course you can; you just have to use a GFCI outlet everytime, rather than one for the circuit.
If you are saying it is a bad idea I agree, but it is possible.

Wade - yeah, I guess you could do it that way. I agree with your statement that it wouldn't be a good idea.

Rob

[Steve Roxberg]

It is an unfinished space, does code really require GFCI circuits? Do they even make a GFCI that supports 20amp, and is grey?

[Joe Chritz]

If I read your question correctly you want to run two circuits of 20 amps each. Alternating individual outlets from circuit to circuit. That wouldn't be hard and you could pull THHN wires or two runs of 12-2w/g NM and feed through the outlet. One keeps going unbroken, the other goes to the outlet.

I am not sure you really gain that much but it is possible. It would be the same as running two conduits next to each other, as long as it is properly sized. When pulling NM bigger is better for conduit.

Joe

[Tom Veatch]

You can share the ground but not the neutral. (unless the wire size is twice as large).

Scott

What if the OP ran one 240v 20amp circuit with a neutral (3 12ga wires, black, red, and white) and used the EMT conduit as the grounding conductor. If the 120v outlets alternated connection to the hot wires (black/red) then there would, in effect, be two 120v 20amp circuits that share the neutral and the ground and be protected by a common trip breaker. The only current in the neutral would be the difference between the two hot legs so it would not exceed the 20amp breaker rating. The only downside I see is both circuits would go down if the breaker tripped. An upside would be the availability of 240v if/when needed.

[Rob Russell]

It is an unfinished space, does code really require GFCI circuits? Do they even make a GFCI that supports 20amp, and is grey?

Steve,

Here are snippets of the applicable section of the NEC:

210.8 Ground-Fault Circuit-Interrupter Protection for Personnel.

(A) Dwelling Units.

All 125-volt, single-phase, 15- and 20-ampere receptacles installed in the locations specified in (1) through (8) shall have ground-fault circuit-interrupter protection for personnel.

(5) Unfinished basements

— for purposes of this section, unfinished basements are defined as portions or areas of the basement not intended as habitable rooms and limited to storage areas, work areas, and the like

GFI receptacles are absolutely available in 20 amp ratings. You can get gray, but that is probably a color you'll have to get from an electrical supply house. Our local big box stores like Home Depot and Lowe's tend to carry white, almond and beige.

[Rob Russell]

What if the OP ran one 240v 20amp circuit with a neutral (3 12ga wires, black, red, and white) and used the EMT conduit as the grounding conductor. If the 120v outlets alternated connection to the hot wires (black/red) then there would, in effect, be two 120v 20amp circuits that share the neutral and the ground and be protected by a common trip breaker. The only current in the neutral would be the difference between the two hot legs so it would not exceed the 20amp breaker rating. The only downside I see is both circuits would go down if the breaker tripped. An upside would be the availability of 240v if/when needed.

Tom,

If Steve did that, he'd need to install a GFI receptacle everywhere. It's cheaper to run another conductor and use the feed-through capability of a GFI receptacle to protect each string of receptacles.

Rob

[Rob Russell]

If I read your question correctly you want to run two circuits of 20 amps each. Alternating individual outlets from circuit to circuit. That wouldn't be hard and you could pull THHN wires or two runs of 12-2w/g NM and feed through the outlet. One keeps going unbroken, the other goes to the outlet.

I am not sure you really gain that much but it is possible. It would be the same as running two conduits next to each other, as long as it is properly sized. When pulling NM bigger is better for conduit.

Joe

If he's running conduit, there is no reason to pull NM-cable and some inspectors will give you grief about running NM in conduit. If conduit is required, he's better off pulling THHN/THWN.

Rob

[Chris Padilla]

Wade - yeah, I guess you could do it that way. I agree with your statement that it wouldn't be a good idea.

Rob

Right...each GFCI protected circuit requires its own neutral so keep that in mind...nearly bit me in my garage rewire. A true multi-wire system has a common neutral returing current for the black and red hot legs. That won't work in a GFCI circuit as you'll need a second neutral.

I hear they make 14/4 now and the second neutral has a red line on it.