Disclaimer: This month’s column involves some basic electrical wiring. Do not attempt electrical work unless you are comfortable and certain of what you’re doing. Improper wiring can result in shock, fires, and even electrocution.
Where I live in western Pennsylvania, power outages don’t usually last for too long. Repair crews often make the needed fixes within hours or perhaps the next day, but I’m a guy who likes to be prepared for things. I can go without a TV and most lights for a few days, but I sure don’t want all the food in our refrigerator to go bad, or to be without the ability to power my (gas) furnace on a cold winter day. A whole-house generator that automatically kicks on would be incredible, but alas, is also very expensive for the little use it would likely see. One solution, and a popular one, is to use a portable gasoline-powered generator to provide a temporary source of electricity.
I might go into how to select and size such a generator in a future column. My generator has two usable 120V outlets, each rated at 20 amperes. I’m smart enough to know that when running, the generator must be outdoors so I don’t kill myself breathing carbon monoxide. My plan is to leave the generator in my detached garage, with doors and windows open, and run two heavy gauge extension cords for the 50 feet or so to reach the house. Obviously, powering certain appliances means being able to get them plugged into the powered extension cords. That presents a group of challenges, like how to plug a furnace in, or leaving a window open so the cords can be brought through.
I came up with the idea presented below perhaps 20 years ago, so don’t have photos showing the particular steps in the implementation. I’ll try to explain what I’ve done in diagrams and with some new photos.
Study this diagram for a bit. It shows the basic concept of interrupting a normal house circuit with an outlet, WITH THE WIRING CONNECTING TABS BROKEN, thus making two independent receptacles on one unit.
Here’s a picture of the tab connecting the upper and lower sets of screws, which must be broken (each side).
One critical thing about using a generator is that whatever it’s powering must be completely isolated from the electrical grid. That protects workers who may be trying to restore power, so that a “dead” line really isn’t being powered by your generator. In the above diagram, I’ve interrupted a wire from my circuit breaker panel, and installed an outlet as shown. With the breaker power to the upper section and the added-on plug inserted there, the circuit functions as it always did. Inserting the plug into the bottom half of the outlet fixture allows that house circuit to be isolated from the electrical panel, but receive power from the generator feed hooked up there.
Generally, the circuit feeding a furnace only feeds that one device, so I installed the above setup on that circuit. Since my generator has two 120V outfeeds, I duplicated this setup for the circuit powering my refrigerator (as well as a few lights and outlets). I should say that my house wiring is old, and yes, I know that lighting circuits and wall outlets are normally on separate feeds.
Here’s a picture of my installation, wall-mounted near the breaker panel. I also have written directions placed nearby on how to use it, and a note to keep the plug inserted in the “normal” location (house panel power) except if the generator is being used.
How do I get the power from the generator to this setup? I have the “generator” side of this outlet setup wired to a weathertight box (lower unit in picture) on the side of my house, within reach of the extension cords from the garage-located generator.
Inside that box are the wires from the two circuits I can power. Each has a MALE plug attached. That’s important. The extension cords being used will have their male ends plugged in at the generator, and have a female end toward the house. If I used a female end in the house junction box, a double-male extension cord would be needed, which would be EXTREMELY dangerous. The plugs in that junction box are wired through the house wall to the generator side of the outlets shown above.
In short, when the generator is running, I can hook up the extension cords to the house-side box, and simply pull the circuit plug in the basement from the breaker panel side of the outlet and insert it into the generator side. That powers the critical circuits and isolates things from the grid.
Sharp eyes will notice that one of my outlets is a 20A unit but the other is a 15A one. That’s one goof I made long ago that I’ve yet to correct. Both should be 15A since that’s the rating for the wires on those circuits.
However, there’s another very important step I took to be sure everything is safe. You may recall I said my generator provides 20A outlets. I wanted to be sure that no more than 15A gets through to the house feed, because my hookup essentially by-passes the protection of the breakers in the house panel. (Yes, the generator has circuit breaker protection, but 20A.)
I built two of these units. Each plugs into a 20A circuit on the generator, but has a fuse wired in so that the maximum amperage drawn through will not exceed 15A.
Here’s a diagram of how the wiring for each of those units was done:
With a fuse inserted into the generator side of the setup, the power goes through the fuse before powering the other side of this receptacle. Using a 15A fuse, then, limits the amount of power drawn through the wires to 15A and protects the house wiring. It essentially plugs into a 20A generator outlet and converts that to a 15A fuse-protected outlet.
I should note that several options are available for commercially made transfer switches, and there are circuit breaker modifications that can be done which “lock” a circuit to a generator and isolate the power, but my setup is completely safe and costs nothing but a few outlets and some wiring. I’ve also noted that there are several internet videos somewhat copying bits of my idea. Those generally convert a hard-wired furnace into a furnace with a wire-and-plug that slips into an outlet on the circuit. That allows you to unplug the furnace and plug it into an extension cord to a generator to supply running power.
If you try any of these ideas, be sure to do so safely, with the power off, the proper wire and connections, etc. Even if this setup is never used, I can rest assured that it’s there, ready for action.
I hope all your projects go well. Thanks for reading, and happy restoring!
Ed
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