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Old 03-15-2010, 11:04 PM   #1
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Back-Feed generator output to bus?


Hello;
If I have a generator that I want to be able to quickly connect when power goes out, and want to connect a plug directly into my SE panel, can I back-feed through a breaker?

I was thinking I would use an approved hook-up receptacle outside, run the correct type and gauge feed cable from that receptacle into my SE panel, through a breaker of the proper type and size, so that when the mains are disconnected (by means of pulling the mains breaker), I can feed circuits throughout the house without having to run any extension cords.

I thought I would post this question here before doing a search of NEC myself. Particularly, because I think such a question might come up frequently after this monster storm we just had in the mid-Atlantic and Northeast.

Thanks for your advice

FW
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Old 03-15-2010, 11:09 PM   #2
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sounds like you are on a reasonable course. One thing you MUST have is an interlock so the mains are turned off anytime the generator can power the system. It is to prevent accidentally killing a lineman by unintentionally backfeeding POCO system.

so, questions?
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Old 03-16-2010, 12:15 AM   #3
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Quote:
Originally Posted by nap View Post
sounds like you are on a reasonable course. One thing you MUST have is an interlock so the mains are turned off anytime the generator can power the system. It is to prevent accidentally killing a lineman by unintentionally backfeeding POCO system.

so, questions?
Sounds like I would need a sub-panel with a transfer switch installed. Feed one side of the transfer switch from a breaker in the main, the other side from the generator, and re-route the branch circuits I want to have backup power to the new sub.
I could handle this kind of work myself, but would absolutely get an inspection before powering it up.



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Old 03-16-2010, 12:28 AM   #4
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It wouldn't have to be a panel. There are simply transfer switches made for the purpose.
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Old 03-16-2010, 12:48 AM   #5
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Quote:
Originally Posted by nap View Post
It wouldn't have to be a panel. There are simply transfer switches made for the purpose.
Something like this?
http://www.homedepot.com/Electrical/...atalogId=10053

Maybe I should buy a large enough genny so I can sell power to my neighbors
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Old 03-16-2010, 12:51 AM   #6
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that is actually a subpanel.

something like this:

http://www.amazon.com/Reliance-TCA10...715059&sr=1-10
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Old 03-16-2010, 01:04 AM   #7
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Here is a popular solution - mechanical interlock that allows the genny breaker OR the main breaker to be on, NOT both.

http://www.interlockkit.com/
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Old 03-16-2010, 01:18 AM   #8
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Quote:
Originally Posted by vsheetz View Post
Here is a popular solution - mechanical interlock that allows the genny breaker OR the main breaker to be on, NOT both.

http://www.interlockkit.com/
that's ugly, but functional
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Old 03-16-2010, 10:21 AM   #9
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Quote:
Originally Posted by vsheetz View Post
Here is a popular solution - mechanical interlock that allows the genny breaker OR the main breaker to be on, NOT both.

http://www.interlockkit.com/
I like that. Inexpensive, and effective, and something I could DIY. The other method, using the transfer switch looks like it requires insertion into the mains, between the meter and the SP. Definitely not a DIY job.


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Old 03-16-2010, 10:52 AM   #10
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How does the transfer switch without the subpanel work to only provide power to certain circuits? Where does it get installed exactly?
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Old 03-16-2010, 11:14 AM   #11
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Let me see if I understand this interlockkit (because if it is what I think it is, it seems pretty ingenous, simple... if not as nap says "ugly").

Basically, you add a double pole breaker that rather than feed power from the panel to a subpanel instead feeds power backwards from a generator to the panel. Then to insure we keep POCO employees save, there is a metal slide that will only allow you to have the "main" breaker "ON" or the "generator" breaker "ON", but not both.
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Old 03-16-2010, 11:18 AM   #12
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the transfer switch without the panel is intended to simply switch the supply to the main panel between gen power and POCO power. If a generator is not capable of handing the entire load, it is not the way to go.


it seems there is something concerning limiting the loads that comes to mind. I remember reading a thread here recently that was dealing with just that point.

any of you other guys remember the thread where it was concerning a generator but the load allowed had to be no greater than the generator could supply?. In other words, you could not simply supply a panel and intend on selectively turning off breakers to limit the load. It had to be designed so the gen could not be overloaded or something such as that.
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Old 03-16-2010, 11:34 AM   #13
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Quote:
Originally Posted by nap View Post
the transfer switch without the panel is intended to simply switch the supply to the main panel between gen power and POCO power. If a generator is not capable of handing the entire load, it is not the way to go.


it seems there is something concerning limiting the loads that comes to mind. I remember reading a thread here recently that was dealing with just that point.

any of you other guys remember the thread where it was concerning a generator but the load allowed had to be no greater than the generator could supply?. In other words, you could not simply supply a panel and intend on selectively turning off breakers to limit the load. It had to be designed so the gen could not be overloaded or something such as that.
I looked over the http://www.interlockkit.com/ web site. It includes the instructions to turn off all breakers before turning on the generator breaker, then turn on only the required breakers that prevent you from overloading your generator. So with the interlock, there isn't anything that will prevent the user from overloading the generator.
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Old 03-16-2010, 11:38 AM   #14
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NEC 700.5 does indicate the emergency system must have capacity for all loads to be served at the same time

I can't find anything (yet) that states it must be able to serve all possible loads



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Old 03-16-2010, 11:56 AM   #15
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That article only applies to legally required emergency systems. You should be looking at Article 702.
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