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I have a portable 6500 W generator. I have a main house electrical panel and a subpanel in my garage, which are on opposite sides of the house. My subpanel is on the outside wall of my garage. The main panel feeds the subpanel.

I would like to connect the generator to the subpanel which would then feed the main panel and then I can decide which breaker (main breaker-OFF) to shut off and which to keep on.

Can this be done? What do I need and how do I do it?

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What is the subpanel for? Is its only purpose to interface to the generator? – wallyk Dec 21 '13 at 3:30

I don't see any way this could be done safely, to code, etc.

Problem being there's no way to interlock the MAIN and the Generator if they are on different panels. Without an interlock, it's quite simply not safe (and in a more nuanced view, if the power company becomes aware of it you may not get your power turned back on - they REALLY don't like that.) The fact that you say you will turn it off is just not good enough. If the service folks are in your area restoring power and they hear a generator running, they very often WILL come check.

It IS possible to have a generator input to the main panel, if the panel manufacturer has an interlock kit for the purpose - I have one. It is not physically possible for the MAIN and the Generator to both be turned on at the same time. The only way you could have it go into the sub-panel would be if the sub-panel was interlocked to disconnect from the main panel, so you absolutely cannot feed the main from the sub, no way, no how.

The generator is portable - when you need it, move it, and provide enough cord from a proper interlocked input on the main panel to connect to it. Or, run new wire all the way to where you want it outside the garage.

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Can you explain briefly what an interlock is and why it can't be placed on a subpanel? – Reid Dec 21 '13 at 17:17
@Reid It's basically an OR switch. The panel is connected to the Mains OR to the Generator, but not to both. This means that the generator cannot backfeed into the mains (and put repairfolk at risk). It cannot be on the subpanel because it must come between the mains and the main panel to work. – bib Dec 21 '13 at 17:39
That pretty much is the third paragraph. Mine is a big hunk of steel that fits over two breakers, my dad's is a little steel toggle that fits between two breakers. Both can be off, but only one can be on. Far less costly but just as effective and legal as a transfer switch. – Ecnerwal Dec 21 '13 at 22:36


You'll likely end up backfeeding the grid, which can easily lead to linemen being injured or killed. A generator should never be connected to the electrical system without a proper transfer switch being installed.

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There is no way to do this safely, and it's certainly against code. Similar to throwing the main breaker and plugging the generator into household outlets, there is simply no way to make it safe. It's not done because it cannot be done safely.

If you want to connect your generator to the outside of the garage (don't operate it inside the garage) then you simply need to install a transfer switch at the main panel, and run a length of cable from the transfer switch to the generator location. It's not as expensive or as much work as you might think, and it provides provably safe power from the generator to all of the house.

There is no other safe way to do this.

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