Optinal Standby Systems

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marmcc

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Article 702.5 states "An optional stanby system shall have adequate capacity and rating for the supply of all equipment intended to be operated at one time." the article goes on to say that "the user of the optional standby system shall be permitted to select the load connected to the system."
I am installing a 25kw (104 output amps) generator in a residence with a 200 amp sevice. I believe I can install a 200 amp automatic transfer switch and connect the 25kw generator to the existing loadcenter. I believe that the the generator does not have to be sized according to the load calculation of the residence (171 amps) because the code allows for the user to select the loads connected to the system. Most homes in Florida have an air handler with a electric heat strip and an air conditioning compressor controllled by a thermostat common to both units. However the heat strip and the air conditioning compressor do not operate at the same time and they are non-coincidental loads. If the user elects not to select the heat strips (2 @ 10kw, the range (12kw) and the electric water heater (4.8kw) then the standby generator has adequate capacity and rating to supply all equipment intended to be used at one time. Have I interpreted this code article correctly, I am having difficulty convincing the local building department.
 
Re: Optinal Standby Systems

If it's a 12 kW range, it's demanded load is 8kW, which combined with your other stated loads, comes to 2.2kW to spare for lights and whatnot. Your generator seems plenty large enough to me, but I could be missing something.

It's an "emergency" generator, for Pete's sake. :D
 
Re: Optinal Standby Systems

marmcc,
Are the nonselected items in a seperate panel and unable to operate while the gen. is running.
Legally Required and Emergency Generators do not allow the user to select what ever they want,they have preselectd loads that must be connected and other loads may not be installed.
Is this of any help??

frank
 
Re: Optinal Standby Systems

I think your heater and AC unit fall under 220.21, and you would only use the larger of either for both the service calculation and the generator calculation.

Other than that, I think you are completely correct. The inspector really thinks you have to size a standby generator for an electric range, heating and hot water all at the same time? 25KW is huge for a residental generator.

Would the inspector require the same size generator if it was a manual switch? Maybe he is thinking the user can't preselect loads if the transfer is automatic. In that case, benaround's suggestion should be enough.
 
Re: Optinal Standby Systems

Originally posted by georgestolz:
It's an "emergency" generator, for Pete's sake. :D
Click to expand...
George this is one of those times where we have to use the correct terms.

Never call a generator an "Emergency Generator" unless that is truly what it is.

The NEC has 3 categories for generators.


ARTICLE 700 Emergency Systems.

Emergency systems are those systems legally required and classed as emergency by municipal, state, federal, or other codes, or by any governmental agency having jurisdiction.


ARTICLE 701 Legally Required Standby Systems

The provisions of this article apply to the electrical safety of the installation, operation, and maintenance of legally required standby systems

The systems covered by this article consist only of those that are permanently installed in their entirety, including the power source.


ARTICLE 702 Optional Standby Systems

The provisions of this article apply to the installation and operation of optional standby systems.
The systems covered by this article consist of those that are permanently installed in their entirety, including prime movers, and those that are arranged for a connection to a premises wiring system from a portable alternate power supply.


The rules are much more restrictive and costly for article 700 emergency systems.

The opening post stated "I am installing a 25kw (104 output amps) generator in a residence"

No typical residence would have an emergency generator, it would have an Optional Standby generator.

The difference between the two is $$$$$.


Call it an Optional Standby for Pete's sake. :D
 
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