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Old 12-14-2009, 12:11 PM   #1
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split feed on 12/3


I am wiring 2 signs, 1 is 15 amp and the other is 20 amps. Can I run 1- 12/3 because the run is around 150 feet and split the feed to the 2 signs. Will the white neutral carry the load with the red and black handling the 15 and 20 amp loads?????

Thank you for any assistance.

Dino

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Old 12-14-2009, 12:13 PM   #2
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split feed on 12/3


Are you feeding both with 20a breakers ?
Or you want to feed one with a 15a breaker & the other with a 20a breaker ?

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Old 12-14-2009, 12:22 PM   #3
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split feed on 12/3


humm, like holy wow batman.

Last edited by evapman; 12-15-2009 at 12:08 AM. Reason: no matter.
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Old 12-14-2009, 12:48 PM   #4
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split feed on 12/3


What kind of signs are these - what lights are powering them ?
Is the actual load 15a & 20a ?
Commercial installation ?
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Old 12-14-2009, 04:33 PM   #5
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split feed on 12/3


Quote:
Can I run 1- 12/3 because the run is around 150 feet and split the feed to the 2 signs. Will the white neutral carry the load with the red and black handling the 15 and 20 amp loads?????

Yes and yes.

I'd just put 20's on both legs though.

remember to make the neutral splice bulletproof where they split. If the conection fails you can end up with 240V to both signs.
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Old 12-14-2009, 07:33 PM   #6
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split feed on 12/3


these are regular signs with 6 fluorescents in each but 1 has a digital read out and that's why it has an extra 5 amp load. I was going to run 12/3 split using each side of the panel and 2 separate breakers, 1 -15 and 1 -20.
From what I understand the 12/3 will run 150 feet with that load on each leg and the neutral white carries the 5 amp difference.

Any other thoughts on this procedure.

Thanks for all the suggestions so far.

Dino
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Old 12-14-2009, 07:43 PM   #7
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split feed on 12/3


At 150' length with #12 you will have over 8v of voltage drop w/15a load (7%)
With a 20a load you will have 11.5v drop...close to 10%
Not sure how well that will work

You are going to run a continous 20a lighting load on a 20a circuit ?
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Old 12-14-2009, 07:46 PM   #8
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split feed on 12/3


I guess I will have to run the 10/3, at least that will give the lights a fighting chance.

Thanks for the input.

Dino
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Old 12-14-2009, 07:49 PM   #9
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split feed on 12/3


I wanted to know how the signs would get 240 across them if the circuit is separate and with 2 switches at the panel?? If the neutral fails, you won't get any current flow, correct??/
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Old 12-14-2009, 07:50 PM   #10
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split feed on 12/3


With #10 it drops to 7% & just over 5%
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Old 12-14-2009, 10:50 PM   #11
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split feed on 12/3


When you have a shared neutral, it is called a "MWBC" or MultiWire Branch Circuit".

With a MWBC, you MUST use a double pole breaker and this now needs to be a tie-bar breaker. Just like a 240 volt circuit.

You CAN'T use one breaker here and another breaker over there or you risk placing them both on the same phase of the panel and this would cause a dangerous overloading of the shared neutral wire!

The breakers MUST be next to each other. This places each hot wire on a different "phase" of the panel. Then they are "opposing" hots.

Because they are "opposing" hots, they can then share the neutral wire without ever overloading it. This is sort of an electrical "trick". Basically one cancels out the other.

This is the same thing as 3 wires coming into a home for your electric service. More google: multiwire branch circuit
http://www.google.com/#hl=en&q=multiwire+branch+circuit&aq=0&aqi=g10&oq= multiwire+&fp=eec9c32d20fe6232

As to the tie bar breaker, this is for safety. Both breakers must be turned off at the same time with the tie bar. What can happen is if you turn off just one circuit and work on that hot and the neutral at the same time (disconnect them), the hot from the other wire can come back around from the other direction via the neutral (through a device which is turned on) and ZAP you!

So the tie bar assures that both hots are turned off at the same time. And I like to identify this as a MWBC in the panel with a label so the next person to come along knows it is not a 240 volt circuit. Rather two 120 volt circuits sharing a neutral.

Last edited by Billy_Bob; 12-14-2009 at 10:56 PM.
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Old 12-14-2009, 11:10 PM   #12
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split feed on 12/3


I found a picture!

Explaining this further (MWBC), ignore the first two drawings in the following picture.

Look at the bottom drawing in the picture. This is AC or Alternating Current which is what the electric company provides. 60 times a second, it alternates. It goes from + to - to + to -, etc.

(Whereas with a car battery, it is DC or Direct Current. It is always + or always -. This would be shown in a drawing as a straight line.)

The 3rd drawing in the picture below shows "opposing" phases or what the two hots would look like in an electric panel at a moment in time. They are "opposite" each other!

When one wire is going to +, the other wire is going to -. Thus on the shared return wire or neutral, if both hots are both using the same amperage, there will be no current flow through the neutral as they cancel each other out!

And the reason you can share a neutral (so long as both hots are on "opposing phases".)



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Old 12-14-2009, 11:42 PM   #13
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split feed on 12/3


Hi Billy Bob,

Thanks for the explanation, that really clears it up for me. I was going to use opposing feeds but I never thought of the tie breaker.

Dino
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Old 12-15-2009, 12:37 PM   #14
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split feed on 12/3


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Originally Posted by dinod62 View Post
Thanks for the explanation, that really clears it up for me. I was going to use opposing feeds but I never thought of the tie breaker.
FYI - The tie breaker is a new requirement. There are MWBC's out there without tie breakers! Be careful! (And a good reason to turn off the main power before working on anything....)
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Old 12-15-2009, 01:24 PM   #15
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split feed on 12/3


After all the info and suggestions, I decided to run 2 circuits and avoid any hassle in the future. No split 3 wire and no breaker ties. The only problem we had was running the 2 lines in since the conduit originally laid in, had a kink in it. Probably done when the pavers came in did the driveway and the curbs but we did it and everything is fine. Thank you to all who contributed. Keep up the great work.

Dino

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