Multiple Runs

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  #1  
Old 02-01-05, 06:10 AM
RetiredAK
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Cool Multiple Runs

Hi! Iím new to this forum but have been reading Q&Aís here for the past couple weeks. Lot of interesting info and good advise. I am currently wiring my new (large) shop and have a question! Shop has a 100 Amp Service Main Breaker. (All outlets and lights are 12-2 wiring and 20 Amp breakers) I park the Motor Home on the side farthest from the breaker panel and have a 30 Amp service (10-2 wiring) running to that wall for it. I want to make four additional runs 120V 20 Amp to the same wall about 70 feet each from service panel total run would be about (100 feet each up through the rafters). My question is can I use four 20 amp breakers and make two runs of 12-3 wire from the breaker box to two separate junction boxes above the wall and then split each one into two separate circuits by splitting the (white) neutral of each run. This would give me the four separate circuits I need. Two circuits would be sharing one (white) neutral back to the breaker box. Each of these runs would power one switched light and four GFI protected outlets for general use (No big loads)

The only reason I was considering this is I have a lot of 12-3 wire and it would be easier and cleaner than making four complete runs (12-2) from Point A to Point B,C,D,E.

Guess my question would be can two circuits share a comman neutral?

Thank You!
Retired
 
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  #2  
Old 02-01-05, 06:44 AM
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The answers to all your questions is yes. Normally I advise against multiwire circuit, but in your case with a long run, it's a good idea. You might do some research on multiwire circuits so you understand the principles. Two hots can only share a neutral if you are very careful to put the two hots on opposite legs of the power (definitely not the same thing as opposite sides of the panel!!). Although not required for your application, I advise you to use 20-amp double-pole breakers, and then put the red on one pole and the black on the other. Put a GFCI in the first box on each hot after you split the 12/3 into two 12/2s. If you do not use a double-pole breaker, then I recommend two single-pole breakers, one above the other, to connect the matching red and black wires.
 
  #3  
Old 02-01-05, 06:44 AM
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You can do this, but you have to be VERY careful. These are called multi-wire circuits, BTW. Each 12-3WG that you run will have two hots--one on black, one on red. These two hots ***MUST*** be on opposite phases of the panel box. This is ***VITAL***. Failure to do this will create a fire hazard.

If you proceed with this plan, I HIGHLY recommend that you feed each multi-wire circuit with a double pole (not a "twin"), 20AMP breaker, rather than two single pole 20AMP breakers. This assures that the black and red are on opposite phases of the panel box, and that someone making changes later doesn't accidentally put them both on the same phase (ie, they move one breaker to make room for a double pole). The only downside is that overloading one "half" of the multi-wire circuit trips both halves of the circuit.


Before proceeding, I recommend that you do a search for "multi-wire circuits". There have been LOTS of discussions here about them.
 
  #4  
Old 02-01-05, 07:12 AM
RetiredAK
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Wink

Thanks!

Your answers are right in my line of thinking. Although I had not thought of using the double- pole breakers. This would be the same as running 240 out of the box and then splitting it to 2-120 lines. I can see where that would be a lot safer for future issues. Insuring two separate legs per run. I will do some more reading before I start this project. Yes the GFCI will be the first outlet on each 120 circuit. I have a lot of wiring to do and Iím sure I will have more questions. I have worked in construction in the past and my knowledge for the most part is just enough so I have the basic ideas but not the technical details. I have a nephew that is an electrician, but when I ask him a question he just wants to come over and do it for me and I donít learn anything that way. After I do a wiring project I do have him check it before I cover it up though!

Thanks Again!
Iíll be Back!
 
  #5  
Old 02-01-05, 08:02 AM
harryhomeowner
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GFCI w/ shared nuetral

I just wanted to clear something up.

Is it ok to share the nuetral between to GCFI recepticles? Would that cause them to trip if the loads in the hots were not equal causing the neutral to carry the difference, therefore a measurable differnec in current on the lines?
 
  #6  
Old 02-01-05, 08:06 AM
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It's okay to share the neutral between two GFCI receptacles. But you can't connect a shared neutral to the load side of a GFCI, so you'd have to use only the line side and put a GFCI in every outlet.

Note that this issue does not apply to this thread, however, since the neutral is no longer shared by the time he gets to the GFCI.
 
  #7  
Old 02-01-05, 08:18 AM
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To try to help clear this up for harryhoneowner...(John, correct me if I'm wrong on this please)

As John said, the neutral can be shared by GFCI's on the LINE side. This is because the GFCI only looks at current differences on the LOAD side (the load side being the actual recepticles of the GFCI, and everything connected to the LOAD lugs of the GFCI). A difference on the LOAD side trips the GFCI, whereas a difference on the LINE side does not.
 
  #8  
Old 02-01-05, 10:51 AM
harryhomeowner
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crystal clear

thanks!!

It's amazing how much info is out there if you ask!!
 
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