Extending Wires For New Breaker Panel *Complicated*

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Old 11-04-07, 09:48 PM
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Extending Wires For New Breaker Panel *Complicated*

I'm finally getting around to my service upgrade, the new meter is set, new service panel is set, passed my first inspection just waiting to get my service cut in by the poco.

My old panel sits two stud cavities from the new panel, I have a few questions.

1) All of my 15 + 20A circuits are too short to be pulled back over to the new panel. Is their any NEC issue with using a 16x16x6 junction box. I'd splice the NM cables to THWN-2 in the box, and run them to the new panel in 3/4 Conduit with no more than 3 current carrying conductors in each conduit.

2)Can I run a #8 ground wire to a ground bar in the 16x16x6, and terminate all the grounds to this?

3)If these are all 15 amp circuits can two circuits share a 12G neutral? I remember reading something in the NEC about sharing neutrals.

4)Any other tips anyone who has had do something like this has for me?

Btw I got lucky all of my high amperage wires were coming from the direction of the new panel so I was able to pull back the range wire, the dryer wire, and the water heater, and central air.

Thanks in advance,

Gabe
 
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Old 11-04-07, 10:13 PM
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Locale inspector permitting you could pull the guts from your existing box and just use it for a J-box. If the breakers are currently exposed with no covering door you would need to fill the breaker slots with blank inserts. Of course you can't bury this in the wall. It must remain accessible.
 
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Old 11-04-07, 10:24 PM
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We often use the old box as a junction.
Have a piece of sheet metal cut and drilled the same size as the old cover for a neat installation.
Opposite phases may share a neutral but it cannot be #12, it should be #14 if that is the conductor size.
The grounds should terminate in the new panel and the junction box should also be grounded.
 
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Old 11-05-07, 06:57 AM
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Why can't a shared neutral be #12? I don't see a problem with that if the circuits are 15 or 20 amps. There is nothing in the code prohibitting up sizing conductors.
 
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Old 11-05-07, 08:21 AM
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Originally Posted by gabe24 View Post
Is their any NEC issue with using a 16x16x6 junction box.
That's okay. You could also just use the old panel box with the guts removed and a flat cover.

I'd splice the NM cables to THWN-2 in the box, and run them to the new panel in 3/4 Conduit with no more than 3 current carrying conductors in each conduit.
You can put many more conductors in the conduit than that. If the conduit is less than 24" in length, the only limit is the number of wires you can install without causing damage to the insulation. If the conduit is greater than 24", you can have up to 9 current carrying conductors assuming all 15 and 20A circuits.

Can I run a #8 ground wire to a ground bar in the 16x16x6, and terminate all the grounds to this?
You have a couple options here. If the boxes are both metal and securely connected with metal conduit, the conduit itself is a legal ground. Simply terminate the grounds in the j-box ground bar and they will be grounded through the conduit to the main panel.

If you'd rather use a ground wire, you only need to install one and it should be sized to match the largest hot conductor. It's okay to make it larger if you want to, but wire bigger than #12 is not required if you only have 20A circuits.

If these are all 15 amp circuits can two circuits share a 12G neutral? I remember reading something in the NEC about sharing neutrals.
You could share the neutrals, but given the very short distance between the boxes I see no compelling reason to do so. Shared neutrals substantially complicate the use of AFCI & GFCI breakers and place restrictions on the breaker position in the panel. In this case, it's best to not deal with it and run a separate neutral for each circuit.
 
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Old 11-05-07, 04:43 PM
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Originally Posted by joed View Post
Why can't a shared neutral be #12? I don't see a problem with that if the circuits are 15 or 20 amps. There is nothing in the code prohibitting up sizing conductors.
You are right.
You can't go the opposite way (i.e., upsize the conductors say to #10 and use a #12 ground).
Sorry, I got myself a** backwards
 
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Old 11-06-07, 12:12 PM
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Sub-Panel?

Why not keep the current junction box as a sub-panel to the new panel? That way you can keep most the current connections, and just run one large cable (6/3, 4/3 or larger) between the two panels. Move only the larger loads, or circuits that are possible to move. Any new circuit should be added to the new panel. A lot less work, and avoids all these messy wire connections and wire nuts, which are a possible source of problems down the road.
 
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Old 11-06-07, 03:20 PM
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Thanks for all the advice, its been extremely helpful.

I was using #12 thwn because I have 3 500 rolls lying around with no use til now.

I'd rather junction all the wires there than leave the lighting / outlet load in a 30 y/o panel and sub it. I ended up using a 16x16 box, with two 1 1/4 peices of emt between. I've got inspection friday hopefully it goes well. I Put a ground bar in the box, and ran a #8 ground wire to it, had extra #8 too.


Thanks again
 
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