Interlock device vs. transfer panel


Old 01-19-07, 01:24 PM
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Interlock device vs. transfer panel

So it looks like we're getting yet another snow storm in the midwest. I have a larger portable gas generator with a 4-prong 30amp twistlock receptacle. For my house, I put in a Generac transfer panel and external inlet port. It took some time, $$ and several trips to the hardware store, but I'm pretty happy with the install.

The problem is, my father split the cost of the generator and now he wants to have a hookup. His main panel is in a finished basement and I'm thinking for this one, I'll put an interlock device on his panel and wire 10/3 to the outside with another inlet box. But I have some questions.

1) Is a manual transfer panel better than an interlock? I know that I have gauges on mine to help balance the load, but he swears that he just wants lights and the furnace blower to run. Shouldn't be too much of an issue. I just hope he remebers to turn off the AC, which would surely knock the generator offline.

2) How is the wiring handled for this? I know I run the two hots to a double breaker and probably the neutral and ground to the bonded ground and neutral bar (this is the main). And then I'll have them running to an inlet box. The interlock device would keep the main and the double breaker from being "on" at the same time. Now that I think about it, are Siemens breakers rated for back feeding? Don't want to burn the house down.

3) How will he know when power is restored? I imagine he could take the panel cover off and wave a voltage sensor over the mains, but is there a better way? Or he could try it every hour or so. Ideas?

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Old 01-19-07, 01:32 PM
Join Date: Sep 2003
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The disadvantages of an interlock are:

You don't know when the power is restored. You have to watch your neighbors, or the street lights, or check every so often.

You don't get the meters that may be built in to the transfer switch.

The advantages of an interlock are:

They are usually cheaper.

You can usually power any breaker (except those larger than the generator power) in the panel.

Yes, you connect the hot wires to the breaker, and the neutral and ground to the appropriate buss(es).

Do not run the generator with the panel cover off. In some cases this defeats the interlock (it depends on the type of interlock).

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