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Old 01-01-2011, 10:15 PM   #1
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SubPanel wiring question


I'm helping my parents add some lights and recepticles (two 120V 15a lighting circuits and two 120V 20a recepticle circuits) to a home built in the late 80's in Texas. Originally it had electric central heat powered by two 240v 60amp circuits. Each was wired with a separate 6/2 cable from the main panel to the attic. When we converted the heat to natural gas the two 240V circuits were disconnected.

I would like to wire a sub panel in the attic to feed four 120V circuits but would prefer not to have to pull cable from the main panel if I can help it.

The question is (from a code perspective) can I use the hot and nuetral wire from one unused 6/2 cable and the hot from the other unused 6/2 cable to wire the sub panel in the attic ( effectively having a 6/3 cable at that point)?

I would then have two black 6 gauge hot wires and a white 6 gauge neutral wired via a 2 pole common internal trip breaker that would feed the sub panel. (each leg of the mains feeding one hot wire and the neutral to the common)

Electrically speaking it would work to carry the load correctly, but since I'm using conductors from two separate cables (though they run the entire length of there run in parallel with each other) is that some violation of NEC?

Sorry for the long winded question. I just don't relish pulling a 3 conductor cable since I doubt I can get it down the wall cavity to the panel without having to use an external conduit to bring the cable from the main panel to the attic.

All help is greatly appreciated. Happy New Year.

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Old 01-01-2011, 10:40 PM   #2
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SubPanel wiring question


In virginia. you have to use 4 conductors, all insulated.black to L1, second black to L2, white to neutral, and the other white to ground, tape it green. dont bond the ground to the box. Should not be common to neutral. At the main panel, the bonding takes place. Call your city electrical office, they should help you with the issue.

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Old 01-02-2011, 07:59 AM   #3
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SubPanel wiring question


The electrical code requires that ALL conductors of the circuit be run together. Your plan will not satisfy this.

You also may not meet the workspace and clearance requirements for the panel in the attic.
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Old 01-02-2011, 08:28 AM   #4
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The electrical code requires that ALL conductors of the circuit be run together. Your plan will not satisfy this.

You also may not meet the workspace and clearance requirements for the panel in the attic.
Thanks for the replies. If where the cables exit the wall cavity into the attic space I placed them both in a rigid conduit from that point to the sub panel would that satisfy the requirement for "run together?

Can you elaborate on the workspace and clearance comment? It is a modest one story home with standing room in the attic where the panel would be placed.

Thanks again.
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Old 01-02-2011, 08:28 AM   #5
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SubPanel wiring question


Are the cables 6-2 with ground? or 6-2 with no ground?

If 2 -2 with ground, I believe you can install a 120 volt sub-panel. A 50 amp 120 volt sub would be plenty for the 4 120 volt circuits you plan.

If 6-2 w/o ground, you are out of luck as Jim P stated.
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Old 01-02-2011, 09:04 AM   #6
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Are the cables 6-2 with ground? or 6-2 with no ground?

If 2 -2 with ground, I believe you can install a 120 volt sub-panel. A 50 amp 120 volt sub would be plenty for the 4 120 volt circuits you plan.

If 6-2 w/o ground, you are out of luck as Jim P stated.
There are two separate 6/2 cables with a bare ground wire of approximately 10ga.

Thanks for the help.
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Old 01-02-2011, 10:03 AM   #7
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SubPanel wiring question


All wire of a circuit must be in the same cable assembly.

Your best option is to install a small 120v sub panel.
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Old 01-02-2011, 07:12 PM   #8
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All wire of a circuit must be in the same cable assembly.

Your best option is to install a small 120v sub panel.
Thanks for the notes. Here is what I did. Comments welcome.

At the main panel I installed two single pole 30A breakers using the two existing 6/2 grounded cables. Each cable feeds half of a 120v, two lug/four space panel which has separate hot lugs. Each lug in the panel holds a twin circuit breaker of 15/20A confirguration so that the result is two 15A lighting circuits and two 20A outlet circuits. The neutral wires and the ground are connected to the neutral bus in the sub panel and the main panel. I did use a ground lug to ground the metal cabinet of the sub panel. For reference the sub panel is less than 25ft from the main panel and is in the attic in an area easily accessible with standing room. Currently one 15A circuit from the sub panel is running 4 can lights in the living room and the others are for future expansion.

Thank you to all for your helpful comments. Any feedback regarding the suitability of the instal would be appreciated.
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Old 01-02-2011, 07:17 PM   #9
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SubPanel wiring question


Pretty sure you need a 240v breaker to feed the panel
And as stated you can't use wires from 2 different cables to feed the panel
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Old 01-03-2011, 08:22 AM   #10
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I also believe your installation is a code violation as to the requirement to have all conductors of a supply feeder in the same cable. I think it is also dangerous as one of your single pole breakers coulf be off and the other half of the panel is still live.

If you plan on leaving the panel as you have wired it, I would at least use a double pole breaker.
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Old 01-03-2011, 07:29 PM   #11
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Thanks. The more I thought about it the more I understand the reason behind the code. Electrically speaking it is over engineered and "safe", at least from a capacity perspective. The violation is in safety of those who might work on it later. That's unfortunate since there are two (Existing) matched, perfectly functional cables run together from panel to panel. I'll be putting a conduit externally from the box to the attic via the eave of the house and pulling a 240V circuit on a double 40 breaker.

Question is: To ground the sub panel, and how? As stated, it is within 25 feet of the main panel. I assume I need a 6/3 with ground and ground the panel via ground strap to the neutral bar where the nuetral and ground wire will attach?
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Old 01-03-2011, 08:04 PM   #12
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SubPanel wiring question


ground and neutral need to be separate.the ground will bond to the metal panel.the neutral will go to a isolated bussbar.you will need to add a ground buss to the panel.

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