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Discussion Starter · #1 ·
Working in an old barn and need to bring power to an outdoor chicken coop. Problem is i need to run 40 amps across the barn and down to a new sub-panel. There is an existing AWG #8/2 cable feeding a 30 AMP outlet that I can use I just need to run a third #8 wire for a ground. Is this ok. The existing 8/2 is new and in good shape. Running the new third wire will be easy and save replacing the entire existing cable. Just want to make sure this is Ok. Thanks for any input.
 

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A distribution panel needs a 4 wire feed. Also all conductors need to be in the same raceway or cable.
 

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It's perfectly fine to retrofit a ground wire in the way you describe. On a 40A circuit, you only need a #10 ground.

It's also possible to feed a subpanel with /2 cable, depending on what circuits will be in the subpanel (they have to be 120V-only, or 240V-only; you can't have both 120V and 240V loads in a subpanel fed by /2 cable).

However... you say the /2 is new. New /2 already has a ground wire in it. Why do you need another?
 

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Discussion Starter · #5 ·
The 8/2 does have a ground I need two hot wires and the 8/2 has a white, black and ground. To get the power to the new sub panel I need a third number 6 wire to be used as a non load carrying back to the main panel. I was planning on zip tying the additional wire to the cable carrying the other three.
 

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A "Handy Husband"
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The 8/2 does have a ground I need two hot wires and the 8/2 has a white, black and ground. To get the power to the new sub panel I need a third number 6 wire to be used as a non load carrying back to the main panel. I was planning on zip tying the additional wire to the cable carrying the other three.
With the existing 8/2 cable with ground, what you have is a hot, neutral and ground. You are missing the second hot. You need a total of 4 conductors: 2 hots, neutral and ground. You cannot run a single conductor with your existing cable to supply the second hot.
 

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OK... consider neutral vs ground.

Neutral is the normal current carrying conductor. As you may know, electricity flows in loops. 240V electricity goes out hot1 and comes back on hot2. 120V electricity flows from a hot and comes back on Neutral.

If you want to have both 120V and 240V loads served out of the same box, you must have a Neutral wire. Neutral wires must be white or gray, always.

Equipment Safety Ground is nothing but a safety shield. No current flows on it normally. It is there to be a "fault catcher" so that current is carried back to the panel (and hopefully causes a breaker trip) instead of electrocuting someone or starting a fire. Grounds must be bare or green.

Modern electrical codes require a totally separate neutral vs ground going to a subpanel. They used to allow them to be combined, but a trivial loose connection on neutral would electrify all the grounds, meaning people touching grounded things would get shocked. They considered that "bad".

So, can you state more clearly what you are trying to do? Also several of us would appreciate if you could describe exactly what your loads actually are. We're trying to find a way to pull this off safely.

Also, what are the distances involved?
 

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Discussion Starter · #9 ·
Thanks for the input and sorry if I was not clear. I am attempting to run a 20 AMP GFCI outlet to an old well so we can pump water out of the well for a garden. I also want to run a second 15 AMP outlet to a chicken coop for security lights. I installed a 70 AMP two slot sub-panel that is 95 feet away from the sub-panel that powers a 150 Ft by 50 Ft pole barn. The existing 8/2 wire runs up 12 feet from the sub-panel that feeds the pole barn and 54 feet across the barn to the second, 70 AMP, sub-panel. I have with the existing 8/2 a ground, which I can use as ground and a black that I can use as a hot and a white that I can use as a second hot. I want to run, a #8 wire to be used as the neutral. The #8 wire will run along and zip tied to the existing 8/2 cable. Hope this is clear. Thanks
 

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Thanks for the input and sorry if I was not clear. I am attempting to run a 20 AMP GFCI outlet to an old well so we can pump water out of the well for a garden. I also want to run a second 15 AMP outlet to a chicken coop for security lights. I installed a 70 AMP two slot sub-panel that is 95 feet away from the sub-panel that powers a 150 Ft by 50 Ft pole barn. The existing 8/2 wire runs up 12 feet from the sub-panel that feeds the pole barn and 54 feet across the barn to the second, 70 AMP, sub-panel. I have with the existing 8/2 a ground, which I can use as ground and a black that I can use as a hot and a white that I can use as a second hot. I want to run, a #8 wire to be used as the neutral. The #8 wire will run along and zip tied to the existing 8/2 cable. Hope this is clear. Thanks
You cannot run a single conductor to use as a hot or a neutral to supplement a 2 wire cable.

Sent from my RCT6A03W13E using Tapatalk
 

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As has already been stated, you can't run an external current carrying conductor outside of a cable that contains its related conductors.

If you had a 120/240 volt well pump that can be adapted to high voltage then there are plenty of 240 volt lights available. Otherwise you'll need to change out the wiring so you have 3 line conductors and a ground.

sorry.
 

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Good plan. When your wires are getting up to #6 Cu though, it's time to seriously consider aluminum. Aluminum has always been fine for feeder. The new AA-8000 alloy even moreso. Good chance the panel lugs will be aluminum anyway.
 

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Discussion Starter · #15 ·
Thanks to all for the valuable input. You guys always come through. Its like having a bunch of wise friends keeping me in code and safe. And I will explore the aluminum.
Safe safe!
 
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