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I have a main panel and a critical loads sub-panel fed by a PV inverter + battery backup. I need to avoid overloading the normal capacity in the critical loads panel (50A), and I'm already at a comfortable max on that for normal use.

However I'd like to be able to run my garage door opener off of that panel selectively, so that I don't have any concerns about tripping the breaker backfeeding that sub-panel, but also be able to easily switch over to backup temporarily to still run the garage door opener during an extended outage.

Is there a standard/easy way to accomplish this? I suppose I could use something like the Square D QO1DM10030TRBR 30-Amp Generator Main Breaker Outdoor Manual Transfer Switch (and just remove the generator twist-lock receptacle from the bottom and instead feed directly from the critical loads sub-panel), but I wanted to see if there was a better way of accomplishing the same thing.

Edit: In an ideal world there'd be a way to a setup a "transfer switch" like this without require breakers in both the panels and in the switch itself.

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  • The likely problem I would see with your last paragraph if I understand what you are suggesting is the transfer switch doesn't appear to switch the neutral, and replacing the single pole breaker with a two pole to switch the neutral (if legal) would not align with interlock mechanism. – NoSparksPlease Aug 19 '20 at 15:10
  • Do GFCI/AFCI breakers switch the neutral? It's in the garage, so those breakers are required anyway here by code. – jcoleman Aug 19 '20 at 15:26
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You have to switch the neutral in your application. Fortunately your garage door load is only 120V, so you can use 2-pole interlocks.

Now, you're overspending on that particular panel. What you're looking at is a common "QO" 8-space panel ($35) + a QO2DTI interlock ($30) + a pricey 100A breaker you don't need ($65) + a common 30A breaker ($16 because QO) + a socket you don't need.

You can buy just the components and avoid the expense of socket and large breaker: just a "QO" 4-space panel + the QO2DTI interlock and 2 2-pole breakers. Don't leave room for anything else in the panel; it's an oddball 120V switched-neutral panel.

An even cheaper way to do this is to bring a receptacle fed from each power source... and right next to that, have an inlet. From the inlet proceed with normal house wiring to the garage door opener (so this section of permanent wiring is isolated from all others). Then have a short 1' extension cord that you plug into the inlet and move to whichever outlet is relevant.

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  • So you're thinking something as simple as this mounted to a standard junction box (mounting it with screws seems a bit odd...but I don't see why I can't make it work)? – jcoleman Aug 19 '20 at 17:51
  • Side note: for anyone who thinks like I do and had to go look it up, this usage of an flexible cord is allowed under the 2014+ NEC Section 400.7(11): "Between an existing receptacle outlet and an inlet, where the inlet provides power to an additional single receptacle outlet. The wiring interconnecting the inlet to the single receptacle outlet shall be a Chapter 3 wiring method. The inlet, receptacle outlet, and Chapter 3 wiring method, including the flexible cord and fittings, shall be a listed assembly specific for this application." – jcoleman Aug 19 '20 at 17:51
  • @jco yess, well done. – Harper - Reinstate Monica Aug 19 '20 at 22:32

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