How do you guys keep from back-feeding the power from your generators back through the power line dropped to your house?
Obviously some of you are just plugging stuff directly into your generators but it sounds like others are full-on powering their entire house.
There are two correct ways:
A double pole (or triple pole) double throw switch.
Or a dedicated transfer switch.
There is some overlap here. One can be the other.
With the double throw switch, you hook the house to the common, and when you throw the switch one way, the house is hooked to the line. When you throw it the other way, the common (house) contacts break from the line and make contact with the generator contacts.
The generator and line contacts never move, and there is no connection between them. The common contacts just go from one to the other.
My big genset uses a commercial transfer switch. It has voltage sensors and timers to crank the generator automatically when the power goes off and switch the house to it.
Then it switches it back and turns the generator off when the power comes back on.
But, the main part is two big three pole single throw relays with auxiliary contacts.
Both of them are normally open, and the output of both are hooked to the house.
The input of one is hooked to the line, and the other to the generator.
The power for the coil to pull in each relay, goes through the normally closed auxiliary contacts of the other.
So, when one pulls in, it kills the connection to the coil of the other. Thus it cannot get power to pull in.
At the same time, each one has a fiberglass non-conductive rod attached that sticks between the contacts of the other when one pulls in.
That way, when one pulls in, the other one physically cannot close because the rod is in the way.
But, if one were to weld shut, and not release when the power to the coil drops out, the other one cannot close.
Because the rod cannot get between the contacts of the welded one which means the other one cannot pull in.
Basically, it means that it is critical that you cannot backfeed the line even by accident.
Remember, transformers work both ways.
That transformer on your pole may be stepping 7,200 volts or 12,470 volts down to the 240 you use in your house.
But, if you put 240 back into it, it will supply 7,200 or 12,470 back down the line to the nearest lineman working on the system.
Trust me, linemen, or the survivors, get really cranky when they find a line that is disconnected from the main source is still hot.........
I know that you are really super careful about pulling the fuses or disconnecting the main before hooking up the generator, but would you put a gun to your head and pull the trigger on the say-so of someone else that its unloaded??
That is how the linemen feel......
. I have no idea how long it will run off the big pig tank in the yard, but with the power out for a couple of days I couldn't see any difference on the gauge. We usually call for a refill when we hit 30%, so even on the low end we could sit through a pretty long power outage. Propane doesn't go bad and doesn't destroy it's own carb. NG is similar, but only available in town. In a real disaster the NG could get turned off, I imagine. But if you don't already have propane at your house, there may be an ordinance against a yard tank and a large tank is a real hassle if you have to drive it in for a refill. Of course, NG is cheaper than propane.
