Generator

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F143744

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Kentucky
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Generator mechanic
Hello, I do generator work, and I have a question. If I have a generator and the main breaker inside is a 100 amp, 240 VA, (generator rated at 19.5kW.) Yet my factory sizing guide says it will produce 210 amps, at a 30% voltage drop. (210A X (240X0.70) = 35,280 watts out of a 19,500 watt generator!

To me that approximately 35,280 watts of power, 210 amps is over double the 100 amp main breaker. Am I correct, a inductive or any load exceeding 100 amps or 24,000 watts will automatically trip the 100 amp breaker at 240 VAC, or can it really supply 210 amps? I have people trying to start large AC units with a LRA of 168 amps, I don’t think that’s possible, especially with the 30% voltage drop.

In other words, how fast does a 100 amp main breaker trip with a overloaded? I am sure it depends on the total wattage being used, Can’t seam to find that answer anywhere.

Thanks...
 
You have to look at the trip curves for the breaker in question. But I don't think the trip curves mean much as in my view ratings of small consumer grade gensets are complete fiction. Very similar to "special"motors used on consumer power equipment such as air compressors.
 
The 210 amps is just marketing BS and does not mean anything. Looking at one breaker manufactures trip curve, their 100 amp breaker will hold 200 amps for at least 30 seconds and up to 5 minutes. It is very unlikely that the generator's prime mover could supply the amount of mechanical energy required to produce that amount of electrical power for a long enough time to trip the breaker.
 
As Don mentioned, a generator's engine would probably get dragged to its knees trying to support a 80% overload before the inverse time breaker tripped somewhere in several minutes time. That's guessing that smaller generators like that, depending on the manufacturer, wasn't already undersized for its nameplate.
 
A lot of generator controllers will shut the engine down anyway if overloaded for a predetermined time, usually before the breaker has a chance to trip on overload.
 
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