I built a shed behind my house and want to use it as a small living space in the event of loss of power that can be heated/cooled. The shed is powered by a 30 amp breaker set and has four wires to the building.

I was hoping to connect the manual transfer switch I bought in line with the input power but came across an issue. The shed is 3 wires and I don’t know what to connect to what. When I started there was a black and red tied together and black/black, white/white, green/ground.

I tied all four black/reds together and the generator works to power the house but now I can’t shut the feeder breaker. What am I doing wrong?

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*** The picture in the switch from left to right is ground, “utility” white, “utility” black, “load” white, “load” black.

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    Can you post some photos? In particular, your shed's panel, the transfer switch (showing the feeders from the house and from the generator inlet), and the generator's outputs? Also please include clear photos of any labels on these devices. You can use the Edit button at the bottom of your question to upload the photos.
    – maples
    Commented Jul 5, 2022 at 19:00
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    Also, what is the manufacturer and model number of the transfer switch?
    – maples
    Commented Jul 5, 2022 at 19:01
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    If you tied the black red together this would provide only 120v we need the type of transfer switch but it sounds like a dangerous setup and could damage the generator with power on the line or charge the line when power is down
    – Ed Beal
    Commented Jul 5, 2022 at 19:13
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    A picture will be very good, because tying all four reds/blacks together sounds like a bad idea. The kind you hope the breaker trips idea.
    – crip659
    Commented Jul 5, 2022 at 19:24
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    To upload pictures, edit your post and click on the "mountain and sun" icon. There is a limit (I think 2 Meg.), so if they are larger you need to either shrink them on your phone or computer (many different ways to do that) or you can email to [email protected] and get back a shrunk image and link (details at picturepdf.com/shrink ) (Full disclosure: My own web site, totally free, images deleted after an hour, images not published anywhere and I don't see them myself (unless you post them to DIY Stackexchange, of course)). Commented Jul 5, 2022 at 20:01

1 Answer 1


That's a 120V "micro transfer switch" that is only legal on a 15A circuit.

Since you didn't mention having a subpanel, I get the impression you have sockets and lights directly connected to a 30A breaker back at the house, which is a huge code violation and a danger.

And you don't know a darn thing about electrical LOL.

It is not the role of this platform to anticipate and warn you off of every error you could make here, which are many, and I already see "kill you/burn your house down" type blunders already. What is called for is for you to skill up. I think the most efficient way to do that is obtain a book on the subject (e.g. from the library) that feels accessible to you, and and read it through. Google won't do this. It only answers questions, and you don't know which questions to ask. That's why you need a well-rounded primer on the subject.

You only have to do it once and it's a lifelong skill.

Speaking of fatal errors,see where the generator inlet is inside? Your plan is to let an extension cord through a door you'll leave cracked open - right? Yeah, that's rapidly approaching the #1 way Americans die in hurricanes! The door left cracked open for the generator cord draws in carbon monoxide and they find a whole family dead. Been happening a lot lately. You need the inlet to be actually outside so you can close doors/windows all the way. But that gadget is not rated to be outdoors, and won't hold up.

All that said, you have come at the problem from completely the wrong angle. I don't know who ran the 30A 10/3 from the house to the shed, but they were clearly expecting you to install a subpanel to power individual circuits in the shed. (you can't just glom a whole bunch of sockets and lights on a 30A breaker, so if you plan to NOT have a subpanel, you need to change that 30A breaker to 20A.)

So a subpanel changes the picture completely on the generator interlock. Now you should be getting the interlock as part of the panel because it's cheap that way. The Siemens ECSBPK01 and 02 interlocks are under $30. This also lets you easily handle the 120/240V problem that you don't understand yet.

Now, if you don't want a subpanel and are willing to downgrade the main panel breaker to 20A, then you can wire the house as a Multi-Wire Branch Circuit or MWBC. Again, stuff you don't know. At that point you can designate half the MWBC to be NOT on generator, and the other half to be ON generator (and place house loads on the appropriate side of the MWBC). And then, the gadget you have could be used as the interlock. However you must understand, that tactic won't support much in the way of appliances. That interlock you have is really limited and is really intended for single 120V loads like a furnace.

However for my money I'd say "send that back" until you have skilled up some more, and allowed those new skills to inform a better plan on wiring the shed.

  • Thanks for the time spent on the answer. I didn’t mention the sub panel because it is downstream the switch I am trying to install. The switch is inside the shed and the intent is to power it with a solar generator and would not be an exhaust issue since it’s a big battery (3.6 Kw).
    – ThatGuy
    Commented Jul 5, 2022 at 21:30
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    @ThatGuy yeah, if you're planning to use a subpanel, you bought the wrong kit, that can't possibly do that, plus it's not rated for 30A. Make sure to get a Siemens subpanel so you can use that ECSBPK01 or 02 interlock, can't beat that price! Yes you can feed that 240V interlock from a 120V supply if you don't install any MWBCs in the shed. The battery instead of gen is a great plan, I wish more people would do that. But still, design for a gas generator - people often mis-size the battery system and are forced in a pinch to switch to gas. Commented Jul 5, 2022 at 21:36
  • CO not an issue here because solar/battery (though not in the original question). But I was looking yesterday at generators (had an outage on the weekend, called my electrician about finally getting heavy-up plus generator inlet etc. which I've been waiting for months, he finally got some key parts that have delayed the job...but I digress) and the instructions say to keep it 20 feet away from any inhabited structure. That may be a little extreme (but I have a good spot for it, so OK) but CO is definitely a real concern. Commented Jul 5, 2022 at 21:46
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    @manassehkatz 20' is not extreme at all, given CO's uncanny ability to seek out vents and openings (partly: driven by wind or negative pressure in building, possibly caused by wind-whipped draft). If I were to install a generator, I would install a chimney/stack for it. Commented Jul 5, 2022 at 22:02

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