Does this count as two feeds to an outbuilding?

[Ken]

I have a detached garage with a subpanel in it that is fed underground from the main panel in the house. When the electrician wired this up, I mentioned that some day in the future, I might want to have a light on the front of the garage that I could control from the house if I wanted to. Since at the time there was already a trench dug from the house to the garage, he said why don't I throw in a 12/3 UF cable (so it could be a three way switch in the house and garage) and leave the ends hanging in the garage and the house for that potential future use.

So now it's 5 years later, and I still haven't hooked up that cable to a light in the garage, but now I'm wondering what's the correct way to wire this up. As I have since come to understand, you can have only one electrical feed to an outbuilding, so if I have the feed to the subpanel in the garage and this other cable coming in also, it sounds to me like that counts as two feeds, and would not be allowed. On the other hand, could I wire it such that the light on the front of the garage is fed from the subpanel in the garage, and then use that 12/3 feeder as a switch leg back to the house? In that case the garage would have just the one feeder. So would this be the corect way to do this? Or maybe it doesn't matter which end the power comes from?

Ken

[HotRod]

This is not considered a second feed because you will be using the power from the garage to feed the switch in the house. You are not sending power anywhere just turning the power on. Check the web for a three way wiring diagram, this should get you started. Or try to fin my logic below

[HorneTD]

That call is up to the Authority Having Jurisdiction (AHJ) which is the codes way of saying the local inspection authority. Using the cable as a switch leg back to the hose would always be acceptable and would render the question moot.

The other approach that is perfectly valid is to take advantage of the code exception for emergency power and run it supplied from the house with a receptacle just inside the out building. Then if you have to work on the out buildings wiring you power your trouble light and tools from the emergency outlet.

A third approach is to power a post light with a weather proof three way switch. In that way the circuit never reaches the out building.

I cannot speak for your AHJ but most would not be concerned about the power to an outside light as long as the switch were in a completely separate box or a divided box so that when the out building's Building Disconnecting Means is open there will be no power in the outbuildings wiring system. Some would require that the three way switch be labeled as powered from the house. Others would require that it be mounted on the exterior of the building so that all access to the lights wiring would be from outside the building.

I have always preferred the emergency circuit approach for it's obvious advantages for having power while trouble shooting the rest of the buildings wiring. Emergency circuits must be kept entirely separate from other wiring. If the circuit enters a non emergency box the box must be fully divided so that the two circuits cannot effect each other. A four inch square by one and one half inch deep box with a plaster ring and a box divider fill that bill quite nicely as would completely separate boxes.