Mr. Big-stuff ha

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I am installing a generator in south Florida, my piers tell me i can size the generator and feeds to the existing sevice based upon my power bill? I do not see anything in the code that allows for this, The customer has a 1000amp service 3 sets of 600 kcmils they want to have a whole house gen-set, the most power used looking at 1 years reports was around 53 kw. they are saying we could add 125% to that and in turn feed this service with a 250amp feed or a 60kw generator without any loadshedding. This may be fine just don't seem right to me. Please advise
 

iwire

Moderator
Staff member
Location
Massachusetts
If you can get demand data for one year from the power company you could do that. Or if you put a recording meter on it for at least 30 days. Or you can do load calculations.


220.87 Determining Existing Loads. The calculation of a
feeder or service load for existing installations shall be
permitted to use actual maximum demand to determine the
existing load under all of the following conditions:

(1) The maximum demand data is available for a 1-year
period.

Exception: If the maximum demand data for a 1-year period
is not available, the calculated load shall be permitted
to be based on the maximum demand (measure of average
power demand over a 15-minute period) continuously recorded
over a minimum 30-day period using a recording
ammeter or power meter connected to the highest loaded
phase of the feeder or service, based on the initial loading
at the start of the recording. The recording shall reflect the
maximum demand of the feeder or service by being taken
when the building or space is occupied and shall include by
measurement or calculation the larger of the heating or
cooling equipment load, and other loads that may be periodic
in nature due to seasonal or similar conditions.
 

augie47

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Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
We get that a lot here also, but, as Bob states, the power bill is only useful if it has a "demand" charge to indicate the maximum load for a given time period. Knowing how many kwh are used isn't much help as it is total usage not maximum load.
 

fmtjfw

Senior Member
I am installing a generator in south Florida, my piers tell me i can size the generator and feeds to the existing sevice based upon my power bill? I do not see anything in the code that allows for this, The customer has a 1000amp service 3 sets of 600 kcmils they want to have a whole house gen-set, the most power used looking at 1 years reports was around 53 kw. they are saying we could add 125% to that and in turn feed this service with a 250amp feed or a 60kw generator without any loadshedding. This may be fine just don't seem right to me. Please advise

If the answer you got was 53KW not 53KWH then that was a demand value and you can do the calculations. That would give about 220A max demand at 240V (assuming single phase).

Further you can use load shedding to protect the other "emergency" circuits by dumping A/C units by breaking their thermostat circuits (easy and cheap).
 
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