PI: 220.87

[wwhitney]

This PI is meant to clarify what is meant by "demand data" in 220.87.

Cheers, Wayne

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 (the highest average kilowatts reached and maintained for a 15-minute interval)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 (the highest average kilowatts reached and maintained for a 15-minute interval) 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 might be periodic in nature due to seasonal or similar conditions. This exception shall not be permitted if the feeder or service has a renewable energy system (i.e., solar photovoltaic or wind electric) or employs any form of peak load shaving.
2. The maximum demand at 125 percent plus the new load does not exceed the ampacity of the feeder or rating of the service.
3. The feeder has overcurrent protection in accordance with 240.4, and the service has overload protection in accordance with 230.90.

Statement of Problem and Substantiation for Public Input

At present, 220.87(1) provides no definition of "maximum demand data" or specification of the time interval for averaging. On the assumption that 220.87(1) is intended to use the same definition and 15 minute averaging interval as the exception, that language belongs in 220.87(1), not the exception. The word "continuously" is then removed to avoid any implication that a different averaging interval is required in the exception.

 

[ron]

I suspect that 220.87(1) maximum demand data is meant to apply to utility metering (or similar), but it is not always the case that the utility does their demand measurement based on the highest average kilowatts reached and maintained for a 15-minute interval.
The definition of maximum demand data may block usage of utility metering.

 

[augiekaz]

When we install power meters to measure the demand the CTs are measuring L - N load (120V). But the code seems to suggest we lump the measured demand KW with the new load KW and then divide by L-L voltage (240V). Would this be counting the measured load at half it's amperage (on a single phase 120/240 service)? Would it be more accurate to convert the measured demand to amps and then add that to new load KW / 240V? @charlie b I have seen you comment on 220.87

 

[electrofelon]

Regarding the OP, I would remove the "reached and maintained" words. They are redundant, not necessary, and in fact add confusion and ambiguity.

 

[jaggedben]

Maybe the definition should be something like 'highest average kilowatts reached for any recorded interval not exceeding 15 minutes'.

 

[jaggedben]

When we install power meters to measure the demand the CTs are measuring L - N load (120V). But the code seems to suggest we lump the measured demand KW with the new load KW and then divide by L-L voltage (240V). Would this be counting the measured load at half it's amperage (on a single phase 120/240 service)? Would it be more accurate to convert the measured demand to amps and then add that to new load KW / 240V? @charlie b I have seen you comment on 220.87

If the load is balanced then you are not measuring half the amperage. While it's possible that all the load on a service or feeder could be unbalanced one L-N leg, it's extremely unlikely.