Multi-wire Circuit

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  #1  
Old 09-22-07, 02:09 AM
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Multi-wire Circuit

I am not considering this idea or even need it, but I was curious to know when it is a good idea and how it is accomplished. Like what kind of gauge and circuit breakers are needed, things like that. Like I said, I don't need to do this, but am just wondering the when, why and how of it. Thanks in advance, as there is no urgency in this question.
 
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Old 09-22-07, 02:15 AM
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Not enough info in your post to give specific answers but a search of this board will yield lots of posts on the subject. Forexample: http://forum.doityourself.com/showthread.php?t=318545
 
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Old 09-22-07, 03:03 AM
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This is a good start

http://www.mikeholt.com/newsletters....y&letterID=262


Some the of reasons to do it.... long runs where voltage drop is a concern and load management is equal or near equal on both legs. This is because of return neutral current being cancelled. Example 10 amps on one leg and 10 amps on the other puts 0 amps on neutral. Don't have to calculate the return distance for voltage drop in that case just the distance to the loads. So 200 feet round trip becomes 100 feet as far as voltage drop is concerned... given a perfect example. Lots of electricians use it for their home run then split it. Saves a little in costs. Round wire configuration is a minor advantage in handling when using cable. Pretty good deal when running to a split receptacle....one leg on top receptacle one leg on bottom, tab broken between brass screws ..neutral shared. This is used on the dishwasher and waste disposal commonly.

A dryer circuit is a multiwire if that makes it better to understand.

Hope this helps

Roger
 
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Old 09-22-07, 03:47 AM
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Thanks.

Lets see if I have the setup correct.

2-pole c/b, one half black wire, the other red, white N-bus, ground to G-bus

You must need a j-box for this? splice the 3-wire to (2) 2-wire in the box and wire nut the 3 neutrals together. Where the red will splice with the black of the 2-wire of one and the black of the 3-wire will splice to the black of the other 2-wire. Neutrals must be pigtailed through devices such as outlets, but hot feed can go from screw to screw of different devices? Would this be accepable to use for a gas stove outlet and fridge? I don't have room for a dishwasher and don't plan on having a disposal inthis house. Not that I'm looking for reasons, just curious. Can this be used for bathroom circuits? My kitchen and bath are projects on my long list of to-do. I think the current set up has the fridge outlet on the same circuit with an outlet in the living room, the lights and other rec. are a circuit, and the stove is its own line. My next project is to enclose the side exterior porch that is on the otherside of the kitchen window, it also shares a window of the living room where the outlet is on the fridge circuit.

Think of a shoebox and thats my house, the kitchen is the right toe and living room is the left toe of the shoes and the 2 bedrooms are the left heel and the bath and laundry room are the right heel. I think I may be out of room for a dedicated circuit for the porch area.

Thanks again, since my I don't plan on doing this turned into can I or should I consider this.
 
  #5  
Old 09-22-07, 07:01 AM
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You are confused.

You do not have to split the circuit-ever. You can continue to run the three conductor (plus ground cable) to each and every junction box. You might do this if you were wiring a large room and wanted two circuits, such that the circuits alternated. In this case you MUST pigtail the neutrals. If ever the two hots land on the same device then you MUST use a common trip breaker.

However, you MAY split the circuit at a junction box. In this case, once the circuit is split there is no requirement to pigtail the neutrals. And in this case, as long as you don't have the two hots on the same device, you can actually use two separate breakers, as long as each one is on a different leg of the incoming 240 volt service.

They only make sense in a residential setting if you have a reason for it. One reason would be you want two circuits to an outbuilding, such as a shed. Code allows a multi-wire circuit, but not two separate circuits. Or you have long runs and are concerned about voltage drop. I always recommend a 240 volt breaker, to force separate legs of the service.
 
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Old 09-22-07, 09:13 AM
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So basically, I should not concern myself with this? I would like to be less confused, but I don't need to get things straight at the moment. But let me take a stab at it anyway. Dishwasher/disposal set up. 2-pole breaker, 3 conductor wire running to dishwasher recepticle. Pigtail neutral, black wire to screw, ground to box (if metal) and device. I think this is where I get confused, the red wire. Splice to red of outgoing to disposal recepticle? Where does the black incoming from the disposal go? And where does the black at the diposal go if the red is the hot? If I'm completely wrong, please just tell I'm wrong and I'll move on and never think of it again
 
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Old 09-22-07, 10:21 AM
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In this case you only need 12-2 going to the disposal receptacle. Connect the black of the 12-2 to the red of the 12-3, since the black of the 12-3 is connected to the dishwasher receptcle. In this case you do not have to use a 240 volt breaker, but I do recommend it.
 
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Old 09-22-07, 11:26 AM
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Talking

Roger referred to a dryer as a multi-wire. I would add "yesindidee but not to be confused with a multi-wire circuit". no!!!
 
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