I have two breaker "panels", one is a 200 amp panel for everything in the house, and a separate one (with a different meter) that is just for my electric cold water heater, right next to the other panel, with two 15 amp breakers on it (240v). Now obviously I want to have hot water when the power goes out, but I want to know if I can use the same transfer switch on both panels?

I am guessing no, since I am not hooked up to the same neutral and ground in that electric hot water heater breaker panel.

If I can't, does anyone know why someone would put a separate panel JUST for a water heater? We just moved in this summer, the house is only 15 or so years old too, and it looks like it was done at the time of building the house. Also the breaker panels are in the basement along with the water heater.

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    Can you post photos of the panels involved? – ThreePhaseEel Jan 26 at 22:16
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    “With a different meter” in my part of the world, the most likely reason this would be done is to charge a different rate for consumption. In my area it was once done in “all electric” homes to charge a lower rate specifically for heating. (They don’t do it that way anymore here, but there are legacy accounts where it still exists.) check your billing and see if the rate Kw/hr is the same. – Tyson Jan 26 at 23:12
  • Who is your electric utility? – ThreePhaseEel Jan 27 at 0:16

Your guess is correct. You will not be able to use a single transfer switch in one of the panels to isolate your generator for both panels.

The solution may be to discontinue the use of the water heater specific panel and re-wire the water heater into the main panel. Then the single transfer switch in the main panel would work out nicely.

Keep in mind that there may be reasons why you would not be able to re-wire the water heater or why it was wired to a second panel in the first place:

  1. The main panel may have already been over subscribed for a 200A service and installing a second panel was the overall cheapest solution.
  2. The second panel may have been there to allow separate power usage monitoring for the water heater. This could have been done to share some electrical costs with a roommate that was living with and renting from a previous owner.
  3. The main panel may have already been full of circuit breakers and the second panel was one way to be able to add an electric water heater at one time possibly replacing a natural gas fired heater.
  4. You may not have room in the main panel to add the two pairs of additional dual 240V breakers, one for your water heater and the other for your transfer switch back feed breaker.
  • Thank you for confirming my suspicions, and the explanations! – Brett Hicklin Jan 26 at 23:16

Transfer switches are hokey, substandard, and stupid expensive. Exploit the fact that you have a water heater subpanel, to expand that subpanel out into a generator subpanel. You'll save a ton and have top tier equipment.

I gather the water heater panel is a small one? You want to find a larger panel with enough room for 4 spaces just for a generator interlock kit. Here is one of my favorites, it is $25 and is made for a Siemens panel, and you can get a good sized Siemens main-lug panel for under $100. Other brands have similar things, don't mix panel and breaker brands. That's way cheaper than those hokey transfer switches.

One breaker feeds from your main panel, the other from your genny. Both breakers can't be on at once.

Now you simply relocate any circuits you want on generator to this subpanel. Instead of a measly six, you can have 18, 26 or even 38 circuits, depending on how big a subpanel you got. (you lose 4 breaker spaces to the interlock).

The wiring is simple and straightforward. It supports individual circuit GFCI and AFCI in both modes, since those are downline of the interlock. If you have GFCI on the generator, it is too small for your usage but you need a different interlock for that.

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    I think he has two main panels because he's on a weird two-rate setup.... – ThreePhaseEel Jan 26 at 23:16
  • Thank you for the information! I will look into it! – Brett Hicklin Jan 26 at 23:16

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