Two circuits to receptacles in the same box?
I’m in the planning phase of rewiring my garage/shop. The exisiting receptacles circuits all have issues, or are under sized for the loads I anticipate. So, I want to run: 4 new 20-amp, 120-volt circuits, for the bench top and portable tools; and, two new 20-amp, 220-volt circuits, one for a dust collector, and one for the table saw, jointer, and planer. I want to have two seperate circuits with receptacles adjacent to each other so that if I use the shop vac, to collect dust off the router table, they aren’t both trying to pull off the same circuit. The whole shop has 3/4-inch plywood on the walls, which I would rather not have to tear off and reinstall. So, I intend to surface run EMT. My question is: Can I run two circuits in a single EMT, install receptacles from both circuits in a common box, and be code compliant? I would use two colors of receptacles to make them easily identifiable.
Replies
Best thing to do is to run one 240V circuit. Have half the outlets wired "A" side to neutral, the other half wired "B" side to neutral. Fewer wires to deal with in the boxes, less voltage drop, no worries about multiple circuits in a box (which generally isn't an issue but can get into some hazy areas).
Dan,
In addition to what the other fellows said about hidden problems if the breakers are changed at the main box, you've got to also run a ground wire from the main to your double circuit box. If you don't have that 4th wire, green ground, when you push in one of those little plug checkers it will show an open ground when you check your 110v plugs.
Your idea is a good one if you have a 220v table saw out in the middle of the floor, but you would like to add a 110v drum sander or jointer at the far end of a long set of fence rails. Mounted on the saw itself would be a subpanel for the 220v saw and your 110v equipment.
Don't forget the green ground wire back to the main breaker...,
Bill
Did I say anything about not having a ground wire??
I would assume that a 240V table saw would be on its own circuit (or shared with a few other 240V devices, as the OP suggests). The circuit in question was a general outlet circuit, only the OP wanted it split between two breakers, so that he handle two large loads at once. A split 240V circuit is ideal for this (and, in fact, is required in kitchens in Canada).
Yes.
And a suggestion: run an insulated equipment grounding conductor, even though the EMT itself is allowed per Code to serve as the grounding conductor. Yea, it's more work, but surface-mounted EMT in a home garage/shop can get a lot of abuse, and separate at a coupling. Having the additional wire in there is a backup ground.
Cliff
>>>So, I want to run: 4 new 20-amp, 120-volt circuits, for the bench top and portable tools;
I think you mean 4 new receptacles (not circuits) split between two circuits, right?
If so, then what DanH said.
You can use 12-3 wire for this. Break the little tab on the receptacle that joins the two "hot" tabs, but leave the neutral tab intact. Then you can run the red wire to one hot terminal and the black hot to the other.
You can either split tabs with a single duplex receptacle, or just use two receptacles side-by-side.
If he runs a common neutral, do the two hots (the red and the black) have to be on different busses back in the breaker box?
Yep.
>>>If he runs a common neutral, do the two hots (the red and the black) have to be on different busses back in the breaker box?
This usually happens automatically if you use two adjacent full-sized breakers. It gets a little trickier with the half-size ones.... you need to use either the two inner ones or the two outer ones.
He should NOT run a common neutral back. It makes placing GCFI breakers in there very hard to do, unless he buys the expensive kind... if he can find them.
He didn't say anything about
He didn't say anything about using GFCIs.
I would not run a common neutral for two circuits. If at some time in the future someone moves around the breakers to add a circuit they could put them on the same phase and could cause some real problems. Just keep separate circuits separate. It's one more wire. Big deal.
>>>If at some time in the future someone moves around the breakers to add a circuit they could put them on the same phase and could cause some real problems.
That's rarely a problem. In fact, using split-circuit receptacles is a code requirement here for kitchens.
"using split-circuit receptacles is a code requirement here for kitchens"
Scott, can you explain what this means, so I do not misunderstand.
Are you saying that each kitchen receptacle must be serviced by two different (out of phase) circuits with a common neutral and ground? How do the GFCI receptacles operate, or do you have special GFCI breakers?
"How do the GFCI receptacles
"How do the GFCI receptacles operate, or do you have special GFCI breakers?"
No problem. GFCIs monitor current differences only on their own receptacles and on their load terminals to protect devices downstream.
GFCI receptacles wired to a common neutral on their line terminals will not see any current difference. Remember, the circuit downstream from a GFCIs line terminals is not protected.
OK, so I'm trying to wrap my head around this method of wiring. I'm no electrician but I've done my own for some time... usually with a knowledgeable pro looking over my shoulder before pulling the switch.
I've run two 120 V circuits (two 120 breakers, different sides of the panel) in the same conduit that share the same neutral. That makes sense. But you say to use one 240 V breaker. This does the same thing until one of the lines needs to trip the breaker. Then both circuits go dead. Now I can see why this would be of benefit for the guy going into an outlet box... nothing's live. But perhaps it might not be so good for whatever has been plugged into the two circuits. For instance: the vacuum cleaner shorts out and the computer plugged into the other 120 circuit goes down. It just seems like this method you propose may have some shortcomings.
Or am I not seeing it correctly?
We are not talking about opposite sides of the panel, they are usually on the same bus. They are saying two breakers next to each other.
The safest way to do this is to use a full sized two pole breaker. You can also install a 240v receptacle in that box at this point too. They do make a duplex with a 120v and a 240v receptacle on the same yoke. That would give you the most flexibility. You would have two 120v circuits (3 plugs) and one 240v outlet.
By using a 240V breaker you greatly reduce the chance that some jackleg, some time in the future, will come along and juggle the breakers, putting both circuits on the same leg. Plus, as you noted, there's the safety factor.
Tripped breakers in a normal residential setting (with adequate wiring) are a rarity -- we've never in 33 years had a breaker trip "in anger" in this house. Computers get got for a lot of other more common reasons, such as power failures, tripping over the power cord, etc. Any decent, properly configured computer should be able to handle a power failure from time to time.
Sorry, my computer example was a poor choice. The OP is doing this wiring in a shop. He specifically says he wants to power a vacuum and router table at the same time.... is worried about overload, thus this two circuit in one box thing. So say he's working away on the router and something happens to the vac and it trips the breaker. Both it and the router are de-powered if the 240 V breaker is used. He fixes the vac, resets the breaker, and surprise surprise the router springs into life because in all the commotion he neglected to turn its switch to off. Let's hope that the shop cat hasn't chosen the router table for a nap site. Now this all may seem far fetched but its possible. My large stationary machines have magnetic switches to prevent accidental start up so somebody must have had it happen.
But the 240 breaker thing is supposed to be code in some places so maybe I'm still not understanding what is happening and what could possibly happen. I'm an inquiring mind.
By the way... if a nitwit is going to mess about in a panel there's no way even the most careful installer is going to prevent him from doing stupid things.
The handle tied breaker has been code for decades if you terminate in the same device (split receptacle) but the 2008 code made it code for all multiwire circuits (shared neutral)