During a recent hurricane power outage I got an electrician to rig a line to go from the 240 V output on my 4kw genset into the outlet of my clothesdryer receptacle. I never used that system because there were dozens of downed power lines in the neighborhood, and I did not want any neighbors to fear for their children's safety even though I had pulled the meter which I had connected to the grid.

Is it safe to backfeed your system in this manner? What are the dangers, if any, as compared to a fully approved transfer switch system?

-- Sir (aface@1600Penn.ave), February 18, 1999

Answers

If what you have is not fully approved, you could very well end up killing a lineman. When the power company discovers that you are using a generator to backfeed, they have a way to fry your generator. Don't do it.

-- zap (zap@zap.com), February 18, 1999.

Yes - as above, hook it up safely, and document how to connect/disconnect from the line (house) supply before starting the generator. If the load plug directly into the plug on the generator, then there is no feedback. (A motor, for example, in the furnace has a plug that is tied directly to the generator. This doesn't feed volts back into the wires coming into the house.

But a "blind" hookup into a receptacle (120 or 240 volts) - without a verified way of first isolating the house - can definitely be dangerous. Consider too the result - you have 240v power into a receptacle, then back into the main house panel. Now, where are you going to get 120v "out" and what are you going to do with it?

-- Robert A. Cook, P.E. (Kennesaw, GA) (cook.r@csaatl.com), February 18, 1999.

Please see the following safety warning for generator owners. <:)=

WARNING

-- Sysman (y2kboard@yahoo.com), February 18, 1999.

There's a safety issue here - let me explicit. My "Yes" was in reply to th eprevious answer, not to the original question.

It's NOT safe to directly backfeed like you indicate. IF you completely disconnect the house from the line (outside power), then you MIGHT be able to to hook into a 240v receptacle, IF a qualified electrician checks the main panel and breakers (the what happens next question) before you trust your next house fire to the temporary fix.

IF a load is dirctly run (plugged into) the generator, then that load can't backfeed into the rest of the house, and the rest of the neighborhood.

-- Robert A. Cook, P.E. (Kennesaw, GA) (cook.r@csaatl.com), February 18, 1999.

Course you could just back feed and then throw your main breaker to insure that you were disconnected from the line. What's the drawback?.......Most of the "can I do this?" questioning comes from people who don't want to pay the money for a transfer switch. Looking for a cheap way around it.

You can take simple steps when you're just going to use the setup once. If, for instance, you could guarantee that you'd fire up your generator, use it for two weeks (or whatever) and the lights would come back on and all problems are solved, there are ways around a transfer switch.

But, what happens if you take the easy way out, the lights come back on for a day -- and then they go off again. On, off, on, off. And, one time you forget about the workaround -- zap goes the linesman!

You're playing with other people's lives. Do it right, please.

-- De (dealton@concentric.net), February 18, 1999.

Please read the warning sysman posted. Just get some extension cords.

-- (.@...), February 18, 1999.

I posted this Thursday afternoon, but I see it didn't take.

I copied the original post here to my brother, who is also installing a back-up generator. Here is his reply:

I read through it - pretty workmanlike job. The only hiccup in the procedure comes here:

"I had to extend the length of several of these wires. I did so by soldering the extra length(s) needed and then protecting the connections with 2, count them, 2 layers of heat shrink tubing. I could have merely used wire nuts for such a wire extention, but I wanted an extra good job done."

Soldered splices are OK in electronics (in fact, they're routine), and this guy's background is in electronics, so I guess that's why he thought he was doing an extra good job by soldering. But 120/240v power transmission is another kettle of fish, because at these voltages and amperages a certain amount of heat is generated along the transmission line - from all those excited electrons shoving each around other in the wire. So, all the electrical codes I've read require either continuous runs or wire-nut splices rather than soldering. You terminate the old wire in a utility box with a strain-relief coupling, and bring the new wire into the box, also through a strain-relief coupling, and then splice them with the appropriate size wire nut. With heavy gauge wire, the splice is done with a copper nut and bolt. Solder's a no-no, because of its low melting point.

As others have noted, you don't need a house fire.

-- Tom Carey (tomcarey@mindspring.com), February 18, 1999.

I guess I kind of got an answer to the question. It's as obvious as the nose on one's face that you have to completely isolate your home system and make sure you don't backfeed the grid to keep from killing a lineman and blowing up your genset at the same time. I thought the context of the original question got that much out of the way. If you're intent on backfeeding the grid system, I guess any idiot could find a way to do it. Obviously an elegant transfer switch would be the best way, that wasn't the question. Oh, well. Maybe someone learned something.

-- Sir (aface@1600Pennsylvania.ave), February 19, 1999.