Triple strands of 12/3

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  #1  
Old 01-09-11, 11:30 AM
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Triple strands of 12/3

I had my generator wired directly into my circuit box. I had a 30a 220 breaker, which matches the 30a breaker on the generator. (You get the idea: turn off the service breaker and as many other breakers as necessary; start the generator and turn on its breaker into the box.)

For the wire I used three strands of #12 wire, with two wires each to the 220 poles and to the two grounds. I learned this from a friend and his father. Father was chief of maintenance at a big wood processing plant.

However, a guy who wired a new addition to our house mildly chided me on this. His argument was that unless the two mated wires to a given pole were of identical length, the current would only go down one. Makes some sense. On the other hand, an argument could be made that if that wire began to overload, it would create resistance and the current would flow down the other wire.

In rewiring, I used 10/3 from the box to an outside socket, but still using my old three strand from the generator to the socket.

Thoughts?
 
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Old 01-09-11, 11:47 AM
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There are several problems with this. One you do not have a Code required interlock to prevent the backflow of electricity onto the grid and killing someone. The other is that the conductor sizes used are well below the sizes allowed to be paralleled.

I would advise you very strongly to stop using this dangerous setup.
 
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Old 01-09-11, 12:35 PM
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Thanks for your concern, but could you give me a bit more technical detail.

1) I presume that "Code required interlock" means some sort of switch that will not allow the service breaker on the panel to be switched back on until the generator is disconnected. I know that the high-end generator setups have this.

2) In your third sentence you suggest that with wire that is large enough, one could run two in parallel. But this doesn't seem responsive. If the problem is that current will only go down one wire (because they are never going to be identical in length relative to the speed of light) then parallel can never be efficient. If it is never efficient, then it should always be discouraged. But your statement suggests that it is approved in some cases.
 
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Old 01-09-11, 01:26 PM
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You NEVER use a hookup like this for ANY reason. We had a guy locally here lose almost half his home with this type of setup. If the local utility sees it they will yank out your meter. Use a properly installed double throw safety switch or a small generator panel matched to your generators size. Cost anywhere from 150-300 bucks for a small setup. The other question is moot as there is NO safe way to do what you are doing. You can get a generator panel and most will come pre wired so it only takes an hour or so to install, unless you need a longer hook up wire for the exterior. Mine installed in 65 minutes.
Take a quick look here.....these are available locally or on Ebay....
Reliance Controls Corporation The World's Leading Manufacturer of Transfer Switches for Portable Generators
 
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Old 01-09-11, 01:43 PM
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Conductors larger than 1/0 can be paralleled.

If the conductors are not the same length or material the flow between the two will not be equal. You will always have some flow on both unlike what I think your friend was saying.
 
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Old 01-09-11, 02:35 PM
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Originally Posted by pcboss View Post
Conductors larger than 1/0 can be paralleled.
To expand on pcboss' explanation, THEORETICALLY, any wire can be paralleled. Unless the difference in length is significant, the difference in resistance will be so minuscule that the load imbalance will be negligible. In larger engineered environments, these load balances are designed into the ratings of the wires.

But... since we live in the land of code requirements and safety, the NEC does not allow smaller gauge wires to be paralleled. The cost savings (if there is any) doesn't make sense to allow it.

So yes, you really should replace the wire with 4 10ga wires (hot/hot/neutral/ground). Others have mentioned the requirement for a transfer switch as well which is quite necessary as well.
 
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