How can I safely pass power from an extension cord through a shed wall?

Question

I just purchased a shed and would like to run a few things (light, fan, etc.) inside. The shed is not wired for power, so I was going to just run an extension cord to the shed. Rather than drill a hole in the shed for the cord or run it through the window, is there an electrical box that has plugs on BOTH sides so I can plug the extension cord in on the outside, and plug the power strip in on the inside (yes I get I am still having to drill a hole, but it wouldn't be a hole with an extension cord running through it). Basically the box would act as an mini extension cord to transfer power from one plug to another. Is there such a thing?

Answer 1

The right way...

is to dig a trench and run a permanent circuit out there. Only 6" cover for RMC metal conduit, or with GFCI protection at the house, 12" cover using UF cable.

However I gather trenching is an option you've excluded, so on to your question about an inlet and simply running power out there temporarily or powering the shed off a generator or Jackery.

There's a trick

Plugs have prongy things, sockets have slotty things. The system is designed so power sources, which are energized, are never prongy and always slotty. And then conversely, loads which take power (like your toaster), which are dead when not plugged in, are always prongy since they can't hurt you. You teach your child not to stick paper clips in there, now imagine if every household receptacle looked like this?

That would be bad! It would be ridiculously easy to get shocked.

Well, it would be the same story if some nitwit made an extension cord with the prongy things on both ends, known as a "suicide cord". With one end plugged into supply, the other end is now lethal. And it's been tried to death - people are not perfect enough to handle that without frequent bad endings. Not least, someone could trip on the cord and yank out the zappy end.

Meet the inlet

So what happens when a building is the load, that is taking power? We don't think about it with utility power because that is hardwired. But what about an emergency generator hookup (if properly done)? An RV?

Since the building is the load, it needs to have the prongy thing for the above reasons. So when it works like a socket (being attached to a structure and all), but needs to be a load, that's called an inlet.

You've already met; it's that thing in the photo above.

You put that on the shed or RV or food trailer or whatever is inputting power. That easy.

From the inlet you wire to one or more outlets or hardwired loads, even a subpanel if that's appropriate.

The only issue you really get into is packaging, the pictured one is designed to be built into an RV, so you need to find one that you can put in a junction box or that includes its own junction box.

Answer 2

Look up "inlet extension cord". It's an inlet that screws to the side of a shed and has an outlet attached to the back. No electrical installation, it's one piece exactly what you want. You can screw a power bar to the wall inside next to it.

Assuming the shed isn't double walled and that you will be dragging out the extension cord only when in use, and putting it away otherwise, I think this cheap simple approach is best.

If the shed has hollow walls or you will be leaving it permanently powered you should do it right as suggested by Moishe in a comment to Harper's post. Trench etc, full compliance with building regs.

Come to think of it, if you are only using the extension cord when you're in the shed, you could instead of the inlet use a desktop cable gasket. Effectively a 2 inch round window with a plastic cover.

Answer 3

Since the shed isn't moving anywhere, having an RV-style inlet as in Harper's answer doesn't really gain you anything. All it really gets you is the ability to de-wire the shed, ie the shed now looks like an appliance with a cord that detaches, like the socket on the back of your PC. As you're not going to pick up the shed and take it away, de-wiring the outside doesn't help very much.

Instead, you could wire the shed like its own extension cord. Mount a single receptacle inside the shed, connect it to cable that runs out of the shed, with a regular plug on it that plugs into a wall outlet. You'd have to drill a hole for the cord but not pass any plugs through it. This could work around code restrictions in some places that cover hardwired installations but not ones with a plug on the end.

However that's a hack, and if you're going to keep the shed for a long time it would be better to put in a proper hardwired supply, perhaps with its own breaker at the supply end. That's more or less the same work as above, although may require an electrician depending on local code, but you get proper circuit protection in case of overloads - and increases the scope of what you can run from the shed.

Answer 4

I've been there (shed, not wired) and did it differently.

First, you want to dig your cable, ideally below the frost line, at least deep enough that nobody will hit it by accident with a shovel or stick that they decide to push into the yard for whatever reason. I digged mine about a foot deep and haven't had issues. Also, just for extra proctection I ran it through one of those cable tubes.

Now your cable is in the ground, which means you can come up inside the shed, without making an ugly hole in the wall.

And for safety, as others have pointed out, I did it the other way around: Inside the shed, the power line has a fixed connection inside the junction box. The end that connects to the house has a regular end that plugs into the outside power socket.

All of those (cable, junction box, etc.) you can get outdoor-rated (IPS or whatever your location uses).