generator sizing

Status
Not open for further replies.
C

codepounder

Member
Hello, After installing generators and transfer equipment for over 30 years . we have been tasked by our electrical inspectorate to now provide a 30 day analyzer reading to assure the generator is sized appropriately.

The inspectorate is basing this sizing requirement under section 220.87.
Our argument is this code rule is not pertainent to generators. Our installation falls under section 702 of Optional Standby systems. It is also our argument that it is the end users choice as to the size of the generator they want and which loads they choose to operate. It is also our argument that the inspectorate can not enforce a generator to be sized to the full current draw x 125% as per 220.87. We certainly want to to comply with code rulings as they pertain. We just can not see where they are going with this..... Any suggestions on the proper way to size a generator for the full load on an existing building? We typically use an analyzer for a 1 week period and use the average current (not peak) to size our generator installs.

Thanks Guys
 
codepounder said:
Hello, After installing generators and transfer equipment for over 30 years . we have been tasked by our electrical inspectorate to now provide a 30 day analyzer reading to assure the generator is sized appropriately.

The inspectorate is basing this sizing requirement under section 220.87.
Our argument is this code rule is not pertainent to generators. Our installation falls under section 702 of Optional Standby systems. It is also our argument that it is the end users choice as to the size of the generator they want and which loads they choose to operate. It is also our argument that the inspectorate can not enforce a generator to be sized to the full current draw x 125% as per 220.87. We certainly want to to comply with code rulings as they pertain. We just can not see where they are going with this..... Any suggestions on the proper way to size a generator for the full load on an existing building? We typically use an analyzer for a 1 week period and use the average current (not peak) to size our generator installs.

Thanks Guys
Click to expand...

Are you still under the 2005 cause I believe it changed in 2008 cycle.
 
Why don't you call for the clients usage of power for a year from the POCO ? Beside the accountant could well have all these numbers!

I frankly don't understand, your saying /arguing that total existing service will not be required to be covered 100 % by the use of a generator and your installing under the optional coverage?

If you read 220.87 then yes it just doesn't seem to be opitional at all.

Seems it'd be a Local AHJ call, as to what is required when one applies a generator, I beleive Florida says cover 100% (now), it doesn't seem very optional.

Welcome to the Forum !
 
Even if your running the whole service, I cannot see them forcing you to pickup the full maximum load, because loadshedding is relatively easily done, HVAC units can be shut down or stages removed with a simple relay.
 
codepounder,

If you are truley installing 702 Optional Standby Systems, I don't see where

the EI dept. has a leg to stand on, unless they have amended a local code on

this installation. A '702' system can't have any 'life saftey' items dependent

on it.
 
Frank,
Take a look at 702.5(B)(2). This is new for the 2008 NEC. If you have an automatic transfer switch the generator has to be sized to run 100% of the load that is connected to the transfer switch or you must have automatic load shedding to drop the load back to match the generator output.
 
generator sizing

Hello gentlemen,

to answer your questions , this generator install is for an office building, there is no life safety equipment (fire pump), only A/C, and lighting and common power. We are located in the Caribbean (Cayman Islands) and we adhere to the NEC. I can appreciate the response of using the 2008 code reference, but we have had this generator sitting for 8 months now trying to get approval, so they can not make the 2008 code retro active ( A COMPLETE OTHER ARGUMENT) .

Thank you for your responses.
 
I would think as long as you have emergency lights to get in or out of the building during a power outage. The size and circuits feed should be up to the customer.
Sizing it to the average load as you have done is okay. IMO
 
don_resqcapt19 said:
Frank,
Take a look at 702.5(B)(2). This is new for the 2008 NEC. If you have an automatic transfer switch the generator has to be sized to run 100% of the load that is connected to the transfer switch or you must have automatic load shedding to drop the load back to match the generator output.
Click to expand...

Don,

Thank you.
 
The requirement is to have full power capability. That would mean being able to provide the maximum power required. If no load shed is included in the scope, I can see the inspector's desire to have a reasonable amount of data to demonstrate the generator is sized properly.

There is always at least two sides to every story, and I have a feeling we are only get a partial picture on this one.
 
When we are doing commercial generating sizing the customer provides 24 months of kilowatt demand readings from their utility records. The engineer normally will add a factor to the peak kilowatt demand. Remember most commercial generators have 50% reserve for motor starts for a short period.
jmtc
 
Status
Not open for further replies.
Top