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Old 04-22-2008, 01:23 AM   #1
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Is this normal?


Just finished up installing the new service panel in my house today.
I will first say that I will never complain about paying an electrician to do the work. You guys earn your money with jobs like this, no doubt about it.

Anyway I found 2 circuits that are brought into the panel via a 12/3 cable. The living room is fed by the red wire, then the hallway is fed by the black. I assume they both share a neutral somewhere else which is brought to the box by the white in the cable, ground as well.
This is the same for the circuit that feeds the master bedroom, red wire feeds this room, black wire feeds other 2 bedrooms with only 1 white and 1 ground coming into the panel.
Is this normal? If I had to guess I would say it's not good to do this but I'm not really sure.

If not I guess I can add that to my list of things to re-do in the near future.

Thanks.

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Old 04-22-2008, 02:19 AM   #2
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Is this normal?


This is normal.

If done correctly, it is not a bad thing. If the loads are balanced, the neutral carrys no load.

Be sure and put the two circuits on different phases/ legs, next to each other. Use a 2 pole breaker (instead of 2 singles) if you want to be 2008 code compliant.

Problems occur when you interrupt the neutral connection's path back to the panel. You can end up with 240V on your 120V circuits. Problems occur when the 2 circuits are put on the same phase/leg. The neutral's load can DOUBLE.

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Old 04-22-2008, 08:40 AM   #3
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Is this normal?


Quote:
Originally Posted by 220/221 View Post
Be sure and put the two circuits on different phases/ legs, next to each other. Use a 2 pole breaker (instead of 2 singles) if you want to be 2008 code compliant.
If he uses a two pole breaker on a multiwire branch circuit, both phase conductors in the circuit will source from the same phase. I'm not familiar with the 2008 NEC, but are we talking about a "twin" breaker that is essentially two breakers linked together that occupy two slots and thereby both A and B phase? Maybe I'm getting my terminology screwy, and need to be set straight.
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Old 04-22-2008, 08:46 AM   #4
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Is this normal?


The two-pole breaker is the correct one. It will engage "opposite" sides of the bus bars.
Please refrain from posting incorrect info, and then mentioning you are not sure. Just don't post.
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Old 04-22-2008, 10:46 AM   #5
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Is this normal?


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Originally Posted by Joba Fett View Post
Please refrain from posting incorrect info, and then mentioning you are not sure. Just don't post.
Wow. Thanks for the very friendly tip.

Let me ask a couple questions then...
If a two pole breaker (one that occupies two slots and separate phases, and is interconnected at the throws) is installed on a multiwire branch circuit, it is compliant with the 2008NEC? Does the 2008 prohibit installation of two individual single pole breakers (adjacent to each other on opposite phases) for each phase of a multiwire branch circuit? I understand how the phasing works, but since I'm not using the '08 code, I'd love some clarification.

I had my terminology backwards I guess.
Where I was going with the original post was to clarify that a "twin" (not two pole) breaker...one that occupies one phase and one slot only but feeds two separate circuits...Should not be used for multiwire branch circuit applications under any circumstance due to the overload on the shared neutral.
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Old 04-22-2008, 11:47 AM   #6
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Is this normal?


Oh great. I guess I need to go back in and check this out since I had to separate both of them because one section now runs to the generator panel and the other stays in the panel.
So right now I have them in a junction box that splits it back out into individual cables, should I follow each phase and make sure that they are still on different ones?

How (or does) the NEC account for this type of set up?
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Old 04-23-2008, 07:30 PM   #7
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Is this normal?


Quote:
Originally Posted by thekctermite View Post
Let me ask a couple questions then...
If a two pole breaker (one that occupies two slots and separate phases, and is interconnected at the throws) is installed on a multiwire branch circuit, it is compliant with the 2008NEC?
Yes that is compliant with the 2008 NEC.

Quote:
Does the 2008 prohibit installation of two individual single pole breakers (adjacent to each other on opposite phases) for each phase of a multiwire branch circuit?
They must be connected with a listed handle tie so both trip or disconnect both ungrounded conductors together.

See210.4B

Quote:
I had my terminology backwards I guess.
Where I was going with the original post was to clarify that a "twin" (not two pole) breaker...one that occupies one phase and one slot only but feeds two separate circuits...Should not be used for multiwire branch circuit applications under any circumstance due to the overload on the shared neutral.
We knew that.

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