220.87?

[charlie b]

Existing building, no new loads being added. Existing small generator provides power via existing ATS to optional standby loads. Plan is to replace the normal feeder to this ATS, thus delivering power from a different panel. Both existing "normal source" and new "normal source" are in the same building, and this is a small portion of the building's overall load. The task at hand is determining the feeder size for the new "normal source."

Question: Do I need to perform a feeder load calculation, or else take a 30 day load measurement, in order to confirm the existing load? I can certainly use 220.87, by taking the maximum measured demand over 30 days, add 25%, and then use the value of "zero" for the amount of new load. But do I have to go that far? Would a shorter measurement be acceptable (e.g., one week), just as a "sanity check," since this really isn't a load addition.

 

[char]

Since you are not adding any load to the system, you should be able to use the same feeder size-unless something looks wrong.

However, when you add your load to a different panel you will need to justify that new load on the panel, and that will require a 30-day metering (or calculation per NEC)

 

[chris kennedy]

The task at hand is determining the feeder size for the new "normal source."

Wouldn't the task at hand be to determine the new laod on the panel supplying power to the ATS?

Question: Do I need to perform a feeder load calculation, or else take a 30 day load measurement, in order to confirm the existing load? I can certainly use 220.87, by taking the maximum measured demand over 30 days, add 25%, and then use the value of "zero" for the amount of new load. But do I have to go that far? Would a shorter measurement be acceptable (e.g., one week), just as a "sanity check," since this really isn't a load addition.

Why? Your not adding any additional loads to the ATS?

Commentary following 220.87.

Additional loads may be connected to existing services and feeders under the following conditions:
1. The maximum demand kVA data for a minimum 1-year period (or the 30-day alternative method from the exception) is available.
2. The installation complies with 220.87(2) and 220.87(3).