Generator Interlock and Back-Fed Mains

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Old 12-14-11, 08:50 PM
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Generator Interlock and Back-Fed Mains

My home was built in the late 70's and has only a 60 Amp electrical service and I'm planning on expanding my garage from a 1-car to a 2-car. As part of the garage expansion, I'm upgrading my electical service to 200 Amp and want to install a sub-panel (main lug) in the garage and add a connection to allow my generator to connect through the main panel. I was planning on using a Square-D QO panels, and it looks like I have a big problem. The generator interlock kit requires that the generator breaker is on the top-right (positions 2 and 4) of the panel. It also appears that the breaker retaining bracket required for the back-fed sub-panel also only works on the top-right of the panel (position 2.)

I want to install a 50-Amp sub-panel in the garage because it will be cheaper (and easier) to install the new wiring. I need about 4 or 5 additional circuits for lighting, outlets, a compressor, furnace, and the hot tub on the porch behind the garage.

What are my options here? If I install a main-breaker panel in the garage instead of a main-lug do I still need a breaker retaining kit in the main panel that feeds the sub-panel? Do I need to install a 200 Amp panel in the garage and connect via a feed-lug in the main panel? Is there another type of panel that I need to install in the house instead? If using the generator breaker with the interlock, does that mean I can't have a sub-panel at all?
 
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Old 12-14-11, 09:15 PM
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I'm confused. Are trying to state that you want to have a sub-panel in the garage and also use that garage panel for the generator connection? If yes, then the answer is no, you cannot use a sub-panel to connect through to the service panel.

The very first thing you need to do is to find out if an interlock is even acceptable to your Authority Having Jurisdiction (AHJ) aka the local electrical inspection agency. Some AHJs do NOT allow circuit breaker interlocks that can be defeated by removing the panel cover.
 
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Old 12-14-11, 10:44 PM
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The main panel will have the generator connection and the feed to the sub-panel. I know I can't feed the generator through the sub-panel.

The problem is that on the main-panel both the generator interlock and the breaker retaining bracket both fit onto the same breaker position (top-right). So if I can't use a mail-lug panel in the garage which I know requires a breaker retaining bracket), can I use a main-breaker panel in the garage without a breaker retaining clip on the breaker that feeds it from the main panel?

In a nutshell, what are my options for feeding a sub-panel when a breaker retaining bracket is not avialable to install in the main panel.
 
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Old 12-14-11, 11:16 PM
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Circuit breaker retainers are only required on back-fed circuit breakers. Since the circuit breaker feeding the garage panel would NOT be back-fed no retainer is necessary and it may be placed anywhere in the panel.
 
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Old 12-15-11, 06:51 AM
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Furd could'nt he use something like this as a sub panal?

TRC1203B Panel/Link | Product Details | Reliance Controls Corporation

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Old 12-15-11, 01:49 PM
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Yes, and no. That panel is set up to be fed through the main breaker/generator breaker combo and supply additional circuit breakers that are installed in the same panel. The loads served by the generator will only be the loads installed in this particular panel.
 
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Old 12-15-11, 05:21 PM
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Thanks Furd for the info!!! A lot of the NEC code is a bit confusing to me since I'm not familar with a lot of the terms. Knowing WHY something is done a particular way helps me understand a lot better. I did a quick google on "back-fed mains" and learned that the retaining clip is required so that the breaker can't be removed accidentially. I guess it also acts as a reminder that the legs may be "hot" even though the breaker is off. I just re-read the section on mail-panel and main-lug panels and it all makes perfect sense now. I can see now why my first post was a bit confusing.
 
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Old 12-15-11, 06:26 PM
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Square D makes panels already set up for a generator.
 
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Old 12-17-11, 01:47 PM
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Square D's "intelligent" whole house generator panels are only for automatic transfer. They also make a line of sub-panels with manual transfer, but you need to move all of the circuits you want on the generator to the new sub-panel. They make an interlock kits that fit all of their residential panels that you can hook up to a generator. With this setup it's a bit more complicated to get generator power up and running but you can supply any circuit in your house with generator power.
 
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