Josuea1990
Member
- Location
- Florida, USA
- Occupation
- Electrician
Can 220.83 (a) be used to calculate the optional standby system (generator) size for a whole house automatic transfer as per 702.4 (b)(2)(a) on a dwelling unit?
Generator sizing
- Thread starter Josuea1990
- Start date
Where in 220.82 does it say the load has to be at least 24kVA?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I believe he is citing the part where it allows you to use that section if it is 100amps or more. 24kw/240 = 24000/240= 100
Oh, got it.
I think 230.79 (C) requires 100A minimum for dwelling units. Perhaps 230.79 is referring to the disconnect rating and 220.82 is referring to the feeder rating but seems to be the same intent overall.
(A) Feeder and Service Load.
This section applies to a dwelling unit having the total connected load served by a single 120/240-volt or 208Y/120-volt set of 3-wire service or feeder conductors with an ampacity of 100 or greater.
(C) One-Family Dwellings.
For a one-family dwelling, the service disconnecting means shall have a rating of not less than 100 amperes, 3-wire.
Birken Vogt
Senior Member
- Location
- Grass Valley, Ca
There is one county that requires us to use their worksheet that is basically the optional method.
Lots of generators get sized by that under 24 kw.
It's all so haphazard across the board.
Realistically, the standard, optional, and 220.83 methods are all designed to prevent overheating of wires, and not really tailored toward generators that will run fine at 100% but will shut down if loaded to 110% even for a few seconds, due to the engine running out of power. Where if it were just wires they would only get slightly warm during that same overload.
But then there is the truth that houses do not use anything close to 3va/sq. ft. run through the formula, and that things like air conditioners do not use anything close to their nameplate, and people do not run their stoves at 67% even once in a while.
Lots of generators get sized by that under 24 kw.
It's all so haphazard across the board.
Realistically, the standard, optional, and 220.83 methods are all designed to prevent overheating of wires, and not really tailored toward generators that will run fine at 100% but will shut down if loaded to 110% even for a few seconds, due to the engine running out of power. Where if it were just wires they would only get slightly warm during that same overload.
But then there is the truth that houses do not use anything close to 3va/sq. ft. run through the formula, and that things like air conditioners do not use anything close to their nameplate, and people do not run their stoves at 67% even once in a while.