Another Genny Question


Old 04-22-07, 05:10 AM
Thread Starter
Join Date: Apr 2007
Location: Near Buffalo, NY
Posts: 4,239
Another Genny Question

I didn't want to hijack the other thread with my long-winded question about emergency backup generators ...

We have frequent power outages and use a 2.5kw portable for the gas furnace, fridge, and selected lighting and other small appliances. Two 12-gauge outdoor-rated extension cords, each with three receps, run from the outdoor genny; one upstairs for the appliances and one downstairs for the furnace.

The fridge, lights, and appliances are powered off one of the 12ga with 14ga grounded cords using the "Green Acres" TV show method: "You can't plug a seven with a two ..."

To power the furnace I kill the breaker, pull the 3 wires out of the furnace's junction box, and attach them to a male edison. It works perfectly, but I'd like to make it permanent so it's easier to deal with.

I bought a Hubbell panel-mount 15a male (part #HBL5278C). I've talked to a couple of hardware-store guys who told me I'll only need one SPDT "three-way" switch to switch the hot between house and genny power.

I'm not really comfortable with that. Shouldn't I also switch the ground and neutral? The genny is grounded to a rod I installed according to the manufacturer's instructions. Switching only the hot won't isolate the genny's ground (or neutral) from the service panel.

Am I correct in this thinking? It has to be one switch so there is no possiblity of energizing the panel-mount male. If so, I'd need a three-pole, double-throw (3PDT) 15a switch. Any part number recommendations?

I'm also questioning the manufacturer's grounding method. Why couldn't I just connect the genny's ground to the panel ground or let it make contact through the 12ga's ground? If I did that, it seems like the single three-way switch would work fine.

Many thanks,
-- RJ
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Old 04-22-07, 05:55 AM
Join Date: Apr 2006
Location: New Bern, NC
Posts: 1,623
I found this interesting diagram.

there was also a good article in ECM this month regarding this topic.

I will also PM you with a link to a forum topic that directly relates to your concern.

The simple answers are that you can just switch the hots, and the equipment ground conductor can serve as the connection between the ground rod at the gen and the homes grounding system. Make sure that the only place where the ground and neutral are bonded is still at the houses main panel.
Old 04-23-07, 09:08 AM
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Join Date: Sep 2005
Location: USA
Posts: 4,119
Isn't there a problem with using a regular DPDT switch for a generator/mains switch? Putting aside the neutral/ground discussion; I thought one of the things that made a transfer switch so expensive is that it's designed to disconnect one connection before making the next connection (break-before-make) to ensure the generator can't backfeed the mains (or vice versa) for even a split second.

Most normal switches aren't designed this way and could "make before break" and effectively short the mains to the generator for a split second.

Am I off track?

Old 04-23-07, 09:36 AM
Join Date: Jan 2007
Location: Central Indiana
Posts: 389
Zorfdt - Most run-of-the-mill SPDT or DPDT switches are of the break-before-make variety, so your concern shouldn't be a problem in most situations. .
Old 04-23-07, 04:12 PM
Join Date: Apr 2006
Location: New Bern, NC
Posts: 1,623
Make before break switchs are more expensive and are hard to find.

We us them in industrial installations, but only when safetys are incorporated that insure phase alllignment.

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