j Slattery
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How do you properly size a residential standby generator to serve AC and heating loads when using a load shedding service rated transfer switch?
Generator sizing
- Thread starter j Slattery
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nollij
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- Washington
Refer to article 220 of the NEC if you are looking for a "specific" calculation method.
If you are lazy and want to power everything in your home during an outage, crank your AC up to full blast, turn on all the lights, lamps, computers, TVs on in your house. Clamp an ammeter onto the incoming line at the main breaker for your distribution panel in your house. Take that number and multiply by a safety factor and get the next standard size generator above that.
Or, you can figure that during a power outage the AC, TV, a lot of the lights, w/e are not necessary and size accordingly to get a cheaper generator.
A more technical response would be that it depends on the loads that it will be servicing (motors, lights, UPSs, computers, etc.). If you have sensitive loads and motors on this generator then it might be worth it to talk to a Generator salesman (CAT, Cummins, Kohler, w/e). They have transient response calculation programs that will determine whether the voltage drop from dropping loads onto the generator will cause equipment to not work properly (or if the GenSet can't handle it). It really depends on how big the compressor is for the AC equipment comparative to the generator size and if the AC starting will cause the computers and more sensitive (to voltage) equipment to drop out.
So, in response to your question, it really depends on the loads and what you plan on doing with it.
If you are lazy and want to power everything in your home during an outage, crank your AC up to full blast, turn on all the lights, lamps, computers, TVs on in your house. Clamp an ammeter onto the incoming line at the main breaker for your distribution panel in your house. Take that number and multiply by a safety factor and get the next standard size generator above that.
Or, you can figure that during a power outage the AC, TV, a lot of the lights, w/e are not necessary and size accordingly to get a cheaper generator.
A more technical response would be that it depends on the loads that it will be servicing (motors, lights, UPSs, computers, etc.). If you have sensitive loads and motors on this generator then it might be worth it to talk to a Generator salesman (CAT, Cummins, Kohler, w/e). They have transient response calculation programs that will determine whether the voltage drop from dropping loads onto the generator will cause equipment to not work properly (or if the GenSet can't handle it). It really depends on how big the compressor is for the AC equipment comparative to the generator size and if the AC starting will cause the computers and more sensitive (to voltage) equipment to drop out.
So, in response to your question, it really depends on the loads and what you plan on doing with it.
What safety factor do you apply or how is it determined?
nollij
Member
- Location
- Washington
If I had a house I was installing it in, I would probably just buy a 3kV GenSet (or whatever was on sale) and figure out what I can and can't run while the power is out.
At work I doubled the size of the expected load on a standby GenSet. But then again, I had a few motors running on it and had to go a bit larger to mitigate the voltage drop when dropping load onto the GenSet.
Maybe a typo there, 3 kV genset?
nollij
Member
- Location
- Washington
qcroanoke
Sometimes I don't know if I'm the boxer or the bag
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Not after 10 minutes.
Seems some people were going back and editing their posts to change what they originally posted.
You know, the old that isn't what I posted excuse.... lol
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