What size transfer switch for generator?

needsometips08November 13, 2010

Our new generator is 7500 watts continuous, 9350 peak. It's 120 volts at 62.5 amps and 240 volts at 31.3 amps.

It has a 120 x 240 30 amp plug in.

Anyone know what size transfer switch we would need to use? We are getting quite conflicting info both in real life and with internet research.

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It depends on what you want to do with your transfer switch. If you want to power the whole house (not likely considering the size of your generator), you need a switch rated for whatever your service entry is. If you choose to power only part of the house, a smaller switch will do. Here is a pretty good reference to show you the options.

Whichever option you choose, be aware that the ratings of your generator are likely to be overstated to some degree. It will last a lot longer and probably work better if you can limit loading to 6000W or less.

Here is a link that might be useful: switch options

    Bookmark   November 13, 2010 at 7:20PM
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The size of the transfer switch will depend on what you are switching. Sounds obvious but let me elaborate a bit. The transfer switch will switch between your two power sources. In your case (a) the generator and (b) power from the power lines connected to your house. The transfer switch will have to handle the larger of the two power demands. So for example if you want have a 200 amp house supply, and your generator. You will need a switch to handle 200 amps. A two hundred amp switch is quite large. May be two feet by one foot by 8 inches. Some people call this a "Frankenstein" switch, just like those old black and white movies. This switch is expensive.

You can however use smaller cheaper switch that will handle less current. Your genset can handle 6500 watts. What some people do is to split off about 6500 watts worth of essential circuits onto a sub panel. The transfer switch is then hooked up only to switch those few circuits. Because the circuits concerned are only a few with a lower current draw, a smaller transfer switch can be used, So 6500 watts / 120v = approx 60 amps or there abouts.

One other scheme popular is to have a bank of small mini-transfer switch of say 20 amps for each circuit. The these transfer switches are about the size of a breaker. You have say 10 of these small switches in a panel box. Because the switches are small they are also cheaper and about the same cost as one larger switch. The smaller switches are easier to switch when compared to a Frankenstein switch, which make a big clunk when it is switched. Good for familly member use, older members, wives, and husbands!!!!!

Hope this gives you some insight and color on how to go about solving your back up genset needs.

Warmest regards, Mike.

    Bookmark   November 14, 2010 at 10:38AM
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