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Thread: Undersized generator?

  1. #1
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    Undersized generator?

    My friend has a 16kw whole-house generator. Her house is 2,000 sf with a 3-ton air conditioner, washer, dryer, range, pool pump, and irrigation pump. How can all this, which comes off of a 150A service, be run on a 65A generator?

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  2. #2
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    Whole house generators are always undersized compared to the service the home has. The assumption comes from the fact that you won't be doing laundry, cooking a thanksgiving turkey and have every light on at the same time. Also, a home very rarely uses 100% of the service it has. I bet the average load on the home is around 80 amps or so give or take. Sizing a generator to supply 100% of the homes "possible" load would be cost prohibitive.

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  3. #3
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    Quote Originally Posted by iwire64 View Post
    My friend has a 16kw whole-house generator. Her house is 2,000 sf with a 3-ton air conditioner, washer, dryer, range, pool pump, and irrigation pump. How can all this, which comes off of a 150A service, be run on a 65A generator?

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    The panel having 150 amps doesn't mean that all of that amperage is being used, nor being used all the time. Also the generator may only be for emergency/power outages, in which case the power usage can be kept to a minimum of only essentials. A question for you: Is it a 65 AMP generator or a 65 KVA?

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  4. #4
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    Quote Originally Posted by iwire64 View Post
    My friend has a 16kw whole-house generator. Her house is 2,000 sf with a 3-ton air conditioner, washer, dryer, range, pool pump, and irrigation pump. How can all this, which comes off of a 150A service, be run on a 65A generator?

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    150 amps being available doesn't mean that all of those amps are being used by the home, nor being used all the time. The actual average usage could be lower than the generator rating.

    I did very light research to come up with this:
    Based on average daily home usage of 48 kwh, a home uses 2,000 watts per hour, which, applied to 120 volt circuits, equals 16 amps per hour. Less when you account for some of those circuits being 240 volt. This would more than be taken care of by that generator.

    (If this is incorrect somehow, I welcome correction. I'm new to this )

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  5. #5
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    Quote Originally Posted by truck41trouble View Post
    Whole house generators are always undersized compared to the service the home has. The assumption comes from the fact that you won't be doing laundry, cooking a thanksgiving turkey and have every light on at the same time. Also, a home very rarely uses 100% of the service it has. I bet the average load on the home is around 80 amps or so give or take. Sizing a generator to supply 100% of the homes "possible" load would be cost prohibitive.

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    I actually prefer your answer to mine.

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  6. #6
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    If you look at your average electric bill, here anyway at my house, you'll see that the demand month-wide is less than 10A constant. 10Ax240V=2400VA or 2.4kw. x 720 hrs/month, that's 1728kw-hrs, x .10$/kw-hr = $173. That is actually very high here, only one month a year does my electric bill go that high, and that's all electric everything. A single 5kw generator could run this place if I ensured the dryer, water heater, and AC weren't all on simultaneously.

    For the generator, we do maintenance and load testing on them all the time. Largest is 22kw, and it's difficult to load one to 90A, even with the oven, dryer, ACs, range, etc all turned on at once.

    HappElectrician, a 16kW genset @ 240V is putting out 66.7A at full load. We routinely install 22kW generators on houses with 400A service. The entire house is not backed up, and large draws like the ACs may be load shed.

    The only thing I can think of that would tank a 16kW generator is a large, on demand electric water heater, or back-up heat strips in an HVAC unit. If those units are gas, no problem. Also, most large purely resistive heating loads cycle via thermostat.
    Electricians do it until it Hertz!

  7. #7
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    Thx

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  8. #8
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    My service is 200A but the POCO transformer is 15kva.
    I only have 1200 sf.

    If I turn on everything I have, I still cannot get to 50A.

    You may want to try that experiment while running on utility then decide if anything needs to be done.
    Advise is a dangerous gift, even from the wise to the wise.

  9. #9
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    Well, it got us through Irma. Thanks for the input.

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  10. #10
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    Oh, and it's a 16 kva.

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