Help with wire count for three circuits..

[Pugly]

After the bum got fired for his botched wire job, I really need to run a 110 circuit to power my sump pump.

The conduit run he put in runs about 50 feet and was supposed to be for three circuits, one for the sump pump, one for the lights and one for the wall plugs, well actually it was supposed to be four as the wall plugs were supposed to be two separate circuits.

The wall plugs and lights are all just normal 110 stuff to plug a TV, desk light, etc, and they are all 12 gauge wire.
My question is how many wires do I need to run through the conduit to power all these circuits. The reason I ask is because when I did my rent house rewire for a couple of circuits, an electrician told me I should have just used one 12-4 wire Instead of two 12-3 wires) and used the white wire as a common, common and the bare wire as a common ground.

If this is correct it would seem that I would need 4 black "power" wires, one white "common" wire and one green "ground" wire. Can you even run the common for more than one circuit? or Two?

I also read somewhere that if you used a common for more than one circuit than the "power" wire needed to be on different legs of the panel so the phasing would not overload the wire.


Have a scared anyone yet? A little assumed knowledge is a dangerous thing.

 

[Charles (in GA)]

What you are describing is known as a "Multi-wire" or "Edison Multi-Wire" circuit. It shares a neutral, and indeed, the two hots must be off of opposite sides of the panel buss. You are required in virtually all cases, to use a double pole circuit breaker with the two handles tied together, the type you use for 240v circuits. This insures that if one side trips and you go to work on it, you won't get zapped by the remaining hot, and it also assures you that the two hots are properly tapped off the two busses of the panelboard.

Multi-wire circuits do not work well with GFCI's however. You either have to separate the two circuits completely and run separate neutrals from the GFCI in the first outlet position, or you have to install GFCI receptacles in every box position. You cannot use GFCI breakers with a multi-wire circuit.

You have to start de-rating wires after you get three hots in a conduit, but it is of no real consequence until you exceed 9 hot wires in a conduit. Be sure and calculate your conduit fill and box fill so you don't exceed the capacity of the conduit and boxes.

Charles

 

[Pugly]

Thanks Charles.
That hardly seems worth the risk of not using a GFCI and it seems I would still have to run two "whites" for four circuits. Is it okay to run one ground wire (green) for all the circuits and just branch them out at the conduit box? It;s got 3/4" conduit so with one green it would be 9 total wires.

 

[ajaynejr]

Run one ground sized for the largest of the (four) hot conductors.

You must run two whites for four 120 volt hot conductors where the four are set up as two multiwire branch aka 120/240 volt circuits.

For MWBC's one white serves no more than one breakered hot wire on each of the hot legs of the system. The white is sized equal to the larger(est) hot wire it serves.

Yes you can get a 120/240 volt GFCI breaker for use on MWBC's but it costs a lot more than an ordinary breaker.

Suppose you were going to run 4 white wires for the 4 hot wires not as MWBC in order to make GFCI installation easier. Given this you can still easily use MWBC from the panel to the first outlet box (7 wires in the conduit) and go non-MWBC from there. The same number of GFCI receptacles (4) would be needed, one for each hot wire.

Example: MWBC from panel to outlet box. Black and white connected to line side of GFCI receptacle. New black and white (12-2 cable) from load side of GFCI to additional ordinary receptacles. Red and also line side white connected directly to an ordinary 12-2 cable to next outlet box. GFCI receptacle there with 12-2 cable continuing on to additional ordinary receptacles. Repeat (duplicate) for the third (black) and fourth (red) hots and separate white of the other MWBC coming from the conduit.

 

[Pugly]

So.....
I am confused, not about the wiring buy about the multi breaker. It's been said that if I want to run a multiwire circuit that I should get a double pole breaker that would kill both circuits that share the Multiwire.
I understand that I would need to have one black wire that was on each leg of my panel so the phasing is right if I run a single white (common) wire, but if I get a double pole breaker, wouldn't that put both legs on the same phase? I tried looking at a bunch of picture on line to see if the breaker was made so it "reached" over to the other leg, but found nothing that helped.


I ask way too many questions.....

 

[VHF]

The panel bus bars are arranged so that alternating rows are connected to opposite legs; this ensures that a double pole breaker always connects to both legs. No "reach over" required!

 

[Pugly]

Man I looked at the panel also, It sure doesn't look that way. It's a GE panel.

 

[theoldwizard1]

The panel bus bars are arranged so that alternating rows are connected to opposite legs; this ensures that a double pole breaker always connects to both legs. No "reach over" required!

+1

Man I looked at the panel also, It sure doesn't look that way. It's a GE panel.

If never seen one made any other way. Required for 240V appliances.

 

[Aceman]

Man I looked at the panel also, It sure doesn't look that way. It's a GE panel.

I'm not too familiar with GE but I think I know what you're talking about as I've came across the same thing in the past. Make sure your looking at a genuine 2 pole breaker and not a twin. GE does some funny stuff with how their buss stabs mount to their breakers.

You can look inside your panel cover to see what kind of breakers to buy. I think they use something like a THQL or some variation of that if it's the type I'm thinking of.

 

[Pugly]

I am going to go look. I am way over my head with this one, but I am down to not much choice but to do it myself.