Home Power Generator Question

July 18, 2015 11:38 AM

Every summer and winter, random weather related power failures (as well as those caused by people knocking down power poles - it's rural with lots of winding roads) leave the house without power for hours to days. So I'm thinking about getting a Generac 8kw gas-powered portable with a manual transfer switch. A Generac 10kw propane powered installed with an automatic transfer switch is at least 6 six times more expensive and I don't see much of an extra benefit.

My question is, the manual transfer switch is rated at up to 8kw. The generator is rated at 8kw with peaking/starting power of 10.2kw. Is the transfer switch rated too low or right on the edge and I should get a 7.5kw generator instead, or will the two work together just fine?

posted by CollectiveMind to Home & Garden (7 answers total)

Do you have a model number for the transfer switch you propose to use? Generally, they will be rated for 30A (7.2kw) or 50A. Obviously, 50A will be fine for your needs. If 30A is enough for you, then you'll be fine with that as well, though obviously you'll need a 30A breaker between the generator and the switch.
posted by ssg at 12:13 PM on July 18, 2015

The transfer switch will be fine. All component ratings have a bit of padding in them. Switch ratings are also worst case for making or breaking under load, and you'll almost certainly be throwing the switch with both the power and the generator off. If you only throw the switch with the generator off you can overload it by a much greater factor without serious risk of harm. It's the arcing when the switch contact opens or closes which does damage and which determines the switch rating.
posted by Bringer Tom at 4:20 PM on July 18, 2015

Response by poster: It's a Reliance 6 Circuit Transfer Switch Kit. The model number is 30216 BRK.
posted by CollectiveMind at 7:10 PM on July 18, 2015

Response by poster: On the Lowes website, it says it's rated at 7.5Kw, but the sales rep for Lowes says believe the rating on the box which is 8kw.
posted by CollectiveMind at 7:12 PM on July 18, 2015

The specs for the transfer switch say 7500 max running watts, so you should be fine with a 7500 max running watts generator. Generac doesn't seem to make a 8kw generator that runs on gas, so perhaps the generator you are buying is actually 7500w anyways.
posted by ssg at 8:32 PM on July 18, 2015

Does this not seem like something you'd have an electrician do, rather than doing it yourself? And if that's the case, I'd expect the electrician to spec the components.

If I'm understanding this right, you'll need to cut power upstream of your main breaker box, probably by pulling the meter. Depending on where you live, this might require permits, an inspection, and/or getting the electric company involved. It's a bit beyond the usual household electric work.

(Electric companies are especially interested in transfer switches because if you connect it wrong, there is the possibility of feeding current upstream into their lines, potentially electrocuting workers repairing damage after a storm.)
posted by ryanrs at 9:49 PM on July 18, 2015 [1 favorite]

Response by poster: I will absolutely have an electrician do this. If the ratings are wrong or don't match, I will switch them out for what does work. Reading the boxes and specs (and comments here), what I have already bought will work and the electrician may have no problem. But if s/he does, I get something else.
posted by CollectiveMind at 9:57 AM on July 19, 2015