GENERATOR SIZING 702.4(B)

[florida-sparkey]

Hello,
I am being asked about a generator on a residence. Home has a 400A service and they want an ATS for the whole home.

As I read it, my first option is using the standard method load calc Article 220 per 702.4(B).

We all know the gen will not need to carry what the load calc comes in at.

702.(B) also says I can use "another approved method". Does anyone know what that means? Is there another method like one put out by the gen set manufacture that will be accepted by the AHJ?

I can do a seperate "emergency" panel with selected loads but this does not meet what the customer really wants so I want to have my ducks in a row before I speak with them.

Thank you!!!!

 

[petersonra]

702.4 Capacity and Rating.
...
(B) System Capacity. The calculations of load on the standby
source shall be made in accordance with Article 220 or by
another approved method.

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 ...

It seems to me that paragraph 220.87 is contained in article 220 so you might want to see if the provision found here is helpful to you. Hint - it will be VERY helpful. Especially if the customer has had a smart meter installed for at least a year.

 

[florida-sparkey]

It seems to me that paragraph 220.87 is contained in article 220 so you might want to see if the provision found here is helpful to you. Hint - it will be VERY helpful. Especially if the customer has had a smart meter installed for at least a year.

Thank you so much sir!!!
I forgot that completely on this. :roll:

I use 220.87 now and again for commercial services and even have a fancy 3 phase recording ammeter for the 30 day recording.

In this case, I think this customer has a smart meter!

 

[LarryFine]

Last one I did with two 200a panels, I used 2 service-rated ATSs, as master and slave units, and used the load-shedding modules to disable the 24v control for the three AC compressors and the one electric-heat indoor unit.

 

[kwired]

I know you said they want to power the "whole home", but with load shedding features you possibly can reduce the size of the generator and still be able to run the "whole home" most of the time with no noticeable interruptions if you shed things like AC, water heater, heat pump or aux heat or at least certain "stages", pool pump...

 

[kingpb]

The problem in sizing for the "whole" house is you have to realistically define what that means; i.e. loads that would actually be needed/used. If you go too big, then you could get into a situation where the EG has a wet stacking problem (diesel) or ash deposits (NG). This occurs because of under loading. You need to load at least 50-60% for long periods, under that you need to limit run time to 30 minutes or so.

An option, if they have the money to burn is to use two smaller units in parallel. Each sized for about 50% of total needed load. The controls easily operate together. This option makes it easier to test the units as well.