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My main panel is 200 amp in my garage, with a 100 amp circuit breaker feeding a panel in the basement. The basement panel powers my electric water heater and well pump, as well as my entire woodworking shop.

During a power outage, I only intend to power the water heater and pump. The transfer switch that I purchased quite a while ago only has 60 amp 2 pole breakers and 5 single pole breakers. Everything I want to power out of the main panel during an outage is 120 volt single pole circuits.

My question is how to wire the remote panel? I suspect that the 60 amp breaker will power both the water heater and the water pump, but I doubt that during normal utility power the 60 amps breaker in the transfer switch will handle my table saw and vacuum system in addition to the HW heater and pump. By the way, I have not purchased the generator yet. I am not a novice around electricity either. My job prior to retirement was wiring municipal power distribution stations, and maintaining water and wastewater pumps and controls.

Rohit Gupta
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David S
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    You initially write "During a power outage I only intend to power the water heater and pump", but then you later write "Everything I want to power out of the main panel during an outage are 120 volt single pole circuits". Does this mean the WH & pump are 120V? Or does it mean that you're not only powering the WH & pump? Where are you planning to locate the new panel - near the main or near the basement? – brhans Jul 03 '23 at 07:43
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    Are you open to returning the transfer switch and getting a different one instead? What make and model is the one you purchased, anyway? – ThreePhaseEel Jul 03 '23 at 11:47
  • In my DIY-but-not-professional-experienced-mind, this seems pretty simple: Hang the transfer switch off of the sub panel. Put the generator input into the transfer switch. Bob's you uncle. This way, neither the wood shop loads nor anything on the main panel get power from the genset, but you get the minimum house electricity you're after. – FreeMan Jul 03 '23 at 12:48
  • I'd like to see the transfer switch. I've seen supply side switches with one double pole switch, and I've seen load side ones with a bunch of 15 and 20amp switches, but I've never seen a transfer switch with a mixture like yours. Is it a residential retail-sold switch? And it's not clear how you're mixing "switch" with "breaker" in the question. – jay613 Jul 03 '23 at 12:55
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    Unless you have an automatic switch, best is to connect to the main panel and then manually set whatever should be On/Off in each panel when running on the generator. Use an interlock instead of a transfer switch and you can potentially power anything, as long as you don't exceed the generator capacity. You're going to need to run a feed from the generator to someplace anyway, most likely that will be a lot easier to the garage (with the inlet on the outside of the wall) than to the basement. – manassehkatz-Moving 2 Codidact Jul 03 '23 at 14:08
  • Also, I assume this is a tanked water heater. If it is tankless, forget about running that on the generator, but I doubt it since most tankless use a lot more than 60A anyway. A tanked water heater will hold temperature for quite a while unless you need to take a hot bath in the middle of a power outage. So if you really want to use a dinky switch, instead of putting it on the subpanel and having to run the generator down to the subpanel, put it on the main panel and run a new circuit for the well pump. Oh, but then you can use an interlock on the main panel and skip the transfer switch, – manassehkatz-Moving 2 Codidact Jul 03 '23 at 14:10
  • so you don't need to run a new circuit for the well pump. Win, win. – manassehkatz-Moving 2 Codidact Jul 03 '23 at 14:11

2 Answers2

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That is the wrong equipment for what you're trying to do - feed loads in two panels. We have searched high and low for a way to do this. It cannot be done safely.

What will do the job is a generator interlock in the main panel. This is a backfeed breaker with a sliding plate interlock to mechanically require the main breaker to be off if the generator breaker is on.

This powers any circuit in the panel, and any subpanel of that panel. Of course you know the generator can't pick up the house's entire load. It is up to you to turn off non-essential circuits in main and subpanel(s) prior to cutting over to generator. However, in exchange for that, you have the freedom to power ANY (not every) circuit in the panel. E.g. if you decide no one will be using water for the next hour, but running the A/C or baking a pie or dryer load would sure be worth the gasoline, you have the freedom to do that.

If that is not your cup of tea, then you can install a "critical loads" subpanel and locate critical loads to that, but then we're back to moving the well pump circuit to the main panel.

And see what Rojit Gupta says: you don't need to power well pump and water heater at the same time. The water heater is a large storage tank that is completely full of water at all times. When you use water, the water pump pushes water through the tank, adding cold water to the bottom and thus pushing hot water out the top - really. It holds temperature for at least 12 hours. So you can shut it off and turn the pump on when you go to actually use the water.

Harper - Reinstate Monica
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If you don't intend to use anything except the water heater and pump during a power outage, then there is no problem.

You can also switch off either of the above manually if you do need to use your saw or other tools.

If you do overload the generator, it will stop, and you can restart it after switching something off. But you shouldn't make this a habit.

I have two water heaters, and I use my home automation to have only one on at a time, so as not to overload my generator when the power has gone. I also switch off my septic system when the water heaters are on. It can handle being off for half a day with no ill effect. In NZ, they are normally designed/rated to hold a few days to a weeks worth of water (before the stages overflow and require a clean).

Rohit Gupta
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    I'm sure it can handle the load, however there is no safe way to split a generator feed to feed circuits in 2 different panels without transferring neutral, which is a PITA in North American wiring because of our two hots. A special circuit would need to be run from main to subpanel any way you approach it. – Harper - Reinstate Monica Jul 04 '23 at 01:11