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My house has a generator transfer switch (ProTran 30310B) attached to circuits in the main panel (see photo).

Transfer switch and main panel

I added an attached garage to the house. I want to add a subpanel in the garage, connecting it via 6-3 cable to a 60 amp breaker in the main panel. I will isolate the neutral bar as usual for a subpanel.

Once I do that, can I migrate my transfer switch and the corresponding circuits from the main panel to the subpanel? The goal is to plug my generator in near the subpanel in the garage and to enable some of the new garage circuits to go onto generator power.

  • If the idea is to run the generator while it is in the garage, carbon monoxide will be an issue. – mikes Jan 26 '14 at 22:45
  • Mikes, the generator cable is long enough that I would wheel it out of the garage to run it, but thanks for the reminder. – Michael H Jan 27 '14 at 3:20
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You could simply pull a properly sized cable from the transfer switch, out to the garage. Then install a generator input receptacle in the garage.

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There's likely a knockout in the bottom of the transfer switch to allow for this. If not, you may be able to add your own (check with the manufacturer).

Moving the transfer switch, and migrating circuits is is likely going to be a huge headache. It's much simpler to pull a single new cable.

  • Thank you--this is a good idea. But I also want to put some of the new garage circuits onto the generator. For this reason I need to know if it's safe to connect a transfer switch to the subpanel. – Michael H Jan 27 '14 at 18:05
  • If the transfer switch is installed properly, there is no danger using it to switch circuits in a sub panel. this answer has a simple diagram of how a transfer switch is wired, that might help you understand why. If the transfer switch is used to switch only one half of a multi-wire branch circuit (MWBC), you could potentially backfeed the service. However, this would also be true in the main service panel. – Tester101 Jan 27 '14 at 18:23
  • No danger using the transfer switch on circuits on the subpanel. That's what I was hoping for. Thanks. – Michael H Jan 27 '14 at 20:42
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From what you wrote, no, you cannot do that so easily.

Your transfer switch is a 10 circuit. Let's assume that 6 of those circuits feed loads in the "new" section of your house, and it would be convenient for you to move the transfer switch to the garage to simplify the wiring of those 6 circuits. I guess that's the impetus for your question?

So far so good. You can install a transfer switch in the garage, connect your generator to it, and power those 6 circuits either from the generator of from the garage sub-panel. Minimal wiring, as the generator is next to the garage.

But what about the remaining 4 circuits from the current transfer switch near the main panel? You cannot power them through the existing 6-3 wire (back-feed).

You could wire a second wire between the main panel and the garage sub panel, to carry the generator power to the existing transfer switch. You would have 2 transfer switches, in parallel.

Another option would be to move the transfer switch to your garage and install extra wires to carry those circuits (4 in my example) back to the main panel. If your transfer switch only switches the hots and not the neutrals, then you need to wire only the hots, for example as individual wires in an EMT conduit.

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