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Old 01-11-2012, 04:59 PM   #1
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Generator/Transfer Switch Question


Hi,

I am trying to figure out how many amp transfer switch to buy. I have a 5000/6250 surge watt generator. If it puts out 120 volts that means the draw at 5000 watts and 120 volts would be 41.67 amps. Right? So why does the generator have a built in 20 amp breaker? Wouldn't that trip at just 2400 watts (20amp x 120v)?

Should I use a transfer switch that is the same amp as the breaker on the generator or can I use a larger one?

Thanks
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Old 01-11-2012, 06:47 PM   #2
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The generator probably has 2 120 volt and 1 240 volt outlets. So 5000/240 = 21 amps.
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Old 01-11-2012, 07:22 PM   #3
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Thank you. I forgot about the 240v plug.
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Old 01-11-2012, 09:52 PM   #4
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Transfer switches are sized to carry the current of the circuit they are transfering. For example if you wanted to transfer a 100 amp service, a 100 amp transfer switch is required, irrespective of the size of the generator.
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Old 01-11-2012, 09:58 PM   #5
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Quote:
Originally Posted by Instantlegend View Post
Hi,

I am trying to figure out how many amp transfer switch to buy. I have a 5000/6250 surge watt generator. If it puts out 120 volts that means the draw at 5000 watts and 120 volts would be 41.67 amps. Right? So why does the generator have a built in 20 amp breaker? Wouldn't that trip at just 2400 watts (20amp x 120v)?

Should I use a transfer switch that is the same amp as the breaker on the generator or can I use a larger one?

Thanks
Do you plan to use your generator power to substitute for the power company's power at your house's main panel (240 Volts)? If so, your non-surge max current draw would be about 22 amps at the 240V outlet. There are many 30 amp transfer switches that will take care of this for you. However, you will have to wacth which appliances you turn on with a 30-amp switch, because your generator won't be able to handle them all at once.

Last edited by Arnold Ziffel; 01-11-2012 at 10:53 PM.
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Old 01-12-2012, 03:00 AM   #6
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Jack's right. There are two ways to set up a transfer switch system, but in both cases the generator's output isn't the main factor affecting the sizing of the transfer switch. You can install a new subpanel with just a few loads to be supported by emergency power, in which case the total load in the subpanel typically does not exceed the generator's capacity. You then install the transfer switch on the feeder to that subpanel, and it needs to be rated for the ampacity of the breaker that feeds it. Alternatively, you can install an ATS on the service feeder to the main panel, so it will transfer the entire building's load to the generator. This requires a transfer switch sized to the service ampacity. If it's automated, it also requires either automatic load shedding or a generator capable of supporting the full load.
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