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I saw one similar question, but I want to be sure if I can do what I would like to do with the transfer switch. Here's the setup:

  • Siemens 200 amp main panel outside wall fed by meter. This panel uses one common bar to terminate both the neutral and ground wires. This panel then feeds a
  • 200 amp Cutler Hammer interior subpanel. The neutral and ground use separate bars.

I want to install the transfer switch to the inside panel which has all the circuits I want to use except one, a 20 amp double-pole breaker for well pump in the OUTSIDE panel. Isn't this virtually like having all breakers in one panel?

So... I would like to route two pairs (red and black) from transfer switch to outside panel to feed the double pole well pump breaker to get water in power outage. Since the neutral and ground from the outside panel feed to the internal panel, then all I need to do is bring the neutral and ground from the transfer switch into the interior panel, right? Bringing those two also to the outside panel would be a no-no ground loop, right?

  • Is this transfer switch a multiple circuit transfer switch, a manual feeder transfer switch, or an automatic transfer switch? – ThreePhaseEel Oct 7 '17 at 0:41
  • Also, is your interior panel type CH or type BR? – ThreePhaseEel Oct 7 '17 at 0:41
  • it is a Connecticut 10 circuit manual transfer switch – dbrown58 Oct 7 '17 at 2:42
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Lucky you

Your panels are set up very advantageously to put in a generator transfer switch. All the loads you want to switch (but one) are already in a subpanel. This makes this super easy. It's almost like somebody planned it... Except the guy who put the pump circuit in the main panel did not get the memo.

You need to put a different transfer switch in between the two boxes. There are a couple ways to do this.

One is fit the subpanel with a manual interlock switch. This is a listed (offically tested) modification to the subpanel where it puts two breakers opposite from each other with a sliding plate so they can't both be on. Simple and cheap, and you may even be able to retrofit your existing panel. Must be thrown manually.

The other way is to pick a spot along the cable between the panels (or elsewhere if you don't mind rerouting cable), cut the cable, and insert the transfer switch inline. This will work with any kind of transfer switch, including automatic. You'll need to cut the cable on one side with enough slack to work, and the other side will be too short so you will have to replace that "half" of the run. So choose location and cut point very carefully to your advantage.

That one breaker in the wrong panel

The stuff you are imagining, you cannot do anything like that. In that approach, the options are break the law, backfeed the grid and kill linemen; or spend a king's ransom on more heavy cables than the underside of an NYC subway car, in a veritable Gordian knot of transfer switch wiring that nobody will be able to figure out after the fact. And the power company and inspector will absolutely hate it.

The right way is easy, if annoying: move the circuit to the subpanel. Extend the pump circuit, all wires, to the subpanel and land it on a double breaker, ground bar, and neutral if used. Do not continue to use the ground in the main panel, in fact if you make this splice inside the main panel, tape the ground wire with green tape to insulate it from the main panel. It's not the end of the world if it grounds accidentally, but grounds must go to the same panel the hots do.

I know that's a pain, but it's way less of a pain than anything else you could do legally.

Not room in the subpanel?

This happens a lot, some guy drove back from the subpanel store slapping himself on the back for saving $30... by buying barely enough spaces. Don't be that guy. You're going to need 6 right off the bat - 4 for the transfer switch and 2 for the well pump.

Worst case you may need to replace the subpanel, and fortujately that is DIY-possible because you can entirely shut off the panel at the main breaker. Also a great time to be looking for transfer switch friendly panels if you want to go that way. Don't scrimp - slap yourself on the back for buying twice as many spaces as you need today. The bigger panels often come with "bonus breakers" which save you some money too.

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    @dbrown58 belay that, I didn't know what kind of transfer switch you meant. Those hokey milti-circuit jobs are a nightmare of wires, and are designed to be a one-stop no-brain solution for paid installers who may be running into God knows what kind of challenge in a customer panel. Since you have a great subpanel setup and don't want to hook up literally 60 wires, I am recommending a big transfer switch that lets you throw the whole subpanel over to mains or gen. This only has 9 wires, but they're fat. – Harper Oct 8 '17 at 21:10
  • Thanks again @Harper. I moved the well pump circuit to the interior sub-panel and now all the circuits I want to energize during power outage are all there. I haven't heard of the "fat" type of transfer switch with only 9 wires before, can you point me in the right direction to view them? – dbrown58 Oct 11 '17 at 23:41
  • @dbrown58 I discuss them in paragraphs 3 and 4. – Harper Oct 12 '17 at 3:10
  • I see one paragraph. Ends in word "fat". But that's ok. I'm all set. Thanks again – dbrown58 Oct 13 '17 at 13:52
  • @dbrown58 paragraphs 3-4 in the answer. ends in words "manually" and "advantage". At that time, I edited my answer to further improve the references there. Did it for you, man. – Harper Oct 13 '17 at 14:51

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