calculating generator load

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P.E.S.

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I have a generator that is 20kw. Aprox 66.7amps @240v and 133amps@120v.
The question I have is, when estimating amperage draw for both 120volt circuits and 240v circuits, which of the max amperage ratings do you use.
 
You don't figure your load based on the amperage, but on the wattage of the load. So for 120V loads the draw is 120 X Amperage = VA or, for all practicle purposes, watts. For 240V loads likewise, 240 X A = watts
 
thanks

thanks

I realize how to compute the load, all I am asking is which max amperage of the generator rating do i use when powering both 240v loads and 120v loads
 
You just need to make sure your total load is less than or equal to the capacity of the generator.

In other words, figure the load you're feeding with 240 V, and then figure the load you're feeding with 120 V, and then add them together. If it is 20 kW or less then you're OK.

Example: You've got 20 Amps @ 120 V and 15 Amps @ 240 V. That is 120*20=2400 W and 240*15=3600 W for a total of 2400+3600=6000 W or 6 kW.
 
PES,

Check with the manufacturer of the gen set, you also have to watch out for starting capacity of your motors, that will eat up kw. They may have a list of typical residential equipment and the wattages. A quick rule of thumb is 2 x HP for motors.
 
P.E.S. said:
I realize how to compute the load, all I am asking is which max amperage of the generator rating do i use when powering both 240v loads and 120v loads
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How did you come up with your amperage values?

The only way a 20kW generator has a max amperage of 66.7A @ 240V is if the 20kW rating is an inrush rating for like motor starting capability. Note 66.7A ? 240V is roughly 16kVA. This 66.7A is more likely the sustained max current rating.

Regardless, whatever the max ampere rating is at 240V is the max the generator will sustain per Line. It has two Lines and your 120V circuits connect one Line to Neutral. Each line is ampere capable to that of the 240V rating. In other words, if the 240V rating is 66.7A max, the max 120V load in amperes you can run on one Line is also 66.7. However, the amperes on each line is the sum of the 240V load in amperes plus the 120V loads in amperes on that line... up to the max.

Also note in many cases, the rated max amperes may be higher than the overcurrent device's trip setting/rating. In operation, running a sustained load at the max ampere rating may trip the overcurrent protection device.
 
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