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I'm looking to install a generator transfer switch to power the well pump as needed. The question I have comes in due to an unorthodox setup - the breaker for the well pump is in the main panel in the cabin, but the disconnect and well itself are about 70ft away in a pumphouse. Also happens to be adjacent to our propane tank (propane genny) and has a lean-to that works nicely to cover the generator in inclement weather. So my question is: can I wire a transfer switch "inline" at the pump house as opposed to powering the main panel? Seems like I could, but main concern is that the breaker would then be "upstream".. would I need another breaker in between the switch and disconnect for when on generator power? Any insight greatly appreciated!

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  • Is the generator only for the pump? What is the pump's breaker size, and its rated power, and what breakers are available on the generator? A lot of portable generators have 15 and 20 amp outlets with suitable breakers in addition to their larger outlets -- does yours?
    – jay613
    Commented May 9 at 20:21
  • There are some issues with grounding with a portable generator, that are especially important here, and different from the typical case of plugging into your main breaker panel, and that are beyond by ability to answer but I think worth asking. Perhaps in a new question once you know your approach and you also know if your generator is bonded or not or adaptable.
    – jay613
    Commented May 9 at 20:29
  • Is your generator a portable unit or permanently mounted, and are you intending this transfer function to be manual or automatic?
    – ThreePhaseEel
    Commented May 10 at 2:55

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Subpanel to the Rescue

Since you only have one circuit, all you need near the pump is a disconnect. However, there is no reason you can't have a subpanel as the disconnect. For example, you could install an 8 space subpanel like this Eaton BR selected from Home Depot for illustration purposes:

8 space panel

  • Two spaces will hold a breaker connected to the feed from the main panel.
  • Two spaces will hold a breaker connected to the generator.
  • Two spaces will hold the pump breaker.
  • Two spaces are available if you would like to use them for wiring up convenience receptacles and lighting.

You then install a generator interlock that fits around the first two double-breakers, allowing one at a time to be ON.

No fancy switch needed. When power goes out:

  • Turn off the utility breaker.
  • Slide the interlock.
  • Turn on the generator breaker.
  • Start the generator.

(There may be reasons to flip the last two steps, consult your generator manual or ask for more details.)

The total cost is pretty low *, and you get the bonus of extra circuits for other uses.

* You may find that a generator interlock that consists of a couple of small pieces of metal and a few screws costs nearly as much, possibly more than, an entire subpanel with case, busbars, etc. But that happens because a lot more subpanels are sold than interlocks, and if you need the interlock you NEED the interlock so you pay the price.

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