220.87 Determining Existing Loads

[JohnHess]

never mind, what I just said was completely off base

 

[brycenesbitt]

A lot of inspectors outright say that there’s no way a 100 amp service on a single-family dwelling can support a 48 amp EV charger because they’ve always seen load calculations of the dwelling being in the 80 amp range.
So when coming to them with data saying that the house is actually under 20 amp, many are just going to call BS. Having guidance from their governing body would prevent this from becoming an issue.

I've put EVSE on an apartment building with 14 units of housing served by a single 100amp breaker.
With no pushback from the AHJ. The cost is a $350 adder for active load management.

Your other approach is a cheap Empora load meter and get 1 second data for a week, including some tests of "turning everything on".
Your AHJ is going to have trouble calling that BS. I keep a loaner Empora just for that purpose, and tether it to a phone if WiFi is not available.

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The POWER working group has been working for about three years to raise awareness of the magnitude of calculation based overestimation of actual load.

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What won't work? Even in my area where power 4-6pm is 61 cents per kWh, I can't argue that the homeowner won't charge at peak times.
Because, they might.

 

[wwhitney]

P.S. I think we've discussed before the idea that for demand data, the utility might record, say, 1 minute average power usage data, and then use a 15 minute sliding window, and the peak demand would be the largest number you can get by summing up 15 consecutive 1 minute average power figures.

In that case, the underlying 1 minute data (not reported to you) is equivalent to kWh used each minute. If you only have 15 minute kWh usage data, you can still provide an upper bound for the 15 minute sliding window peak demand, based on the largest sum of two consecutive 15 minute kWh usage numbers. Because the sum for any 15 consecutive minutes within that 30 minute interval will certainly be less than the sum of all 30 minutes.

However, I don't see the text of 220.87 as requiring the usage of a sliding window, or even such fine grained measurement as 15 minute interval data (for the case of 12 months of data). The 125% factor applied to the maximum observed demand is apparently judged sufficient to cover any undercount attributable to a longer averaging interval.

Cheers, Wayne

 

[JohnHess]

I've put EVSE on an apartment building with 14 units of housing served by a single 100amp breaker.
With no pushback from the AHJ. The cost is a $350 adder for active load management.

Are you talking about the Wallbox? I am eagerly waiting for ChargePoint to include a reasonably priced load management system that could be added to their EVSE.

I just purchased a DCC-12 load shedder for $800 for a job. This thing is a pair of contactors, a circuit board, and a couple CT’s. It just shuts the charger down dead when the load approaches 80% of the service ampacity. I don’t like anything about this.

 

[wwhitney]

Multiplying by 4 is a waste of time. Just find the highest interval and divide it by 15. This is your maximum average demand per minute, but it is still up to the AHJ.

(kWh used during a 15 minute interval / 15 minutes) * 60 minutes/hr = average kW during the interval. And 60/15 = 4. So your procedure also multiplies by 4.

Cheers, Wayne

 

[jaggedben]

P.S. I think we've discussed before the idea that for demand data, the utility might record, say, 1 minute average power usage data, and then use a 15 minute sliding window, and the peak demand would be the largest number you can get by summing up 15 consecutive 1 minute average power figures.

In that case, the underlying 1 minute data (not reported to you) is equivalent to kWh used each minute. If you only have 15 minute kWh usage data, you can still provide an upper bound for the 15 minute sliding window peak demand, based on the largest sum of two consecutive 15 minute kWh usage numbers. Because the sum for any 15 consecutive minutes within that 30 minute interval will certainly be less than the sum of all 30 minutes.

However, I don't see the text of 220.87 as requiring the usage of a sliding window, or even such fine grained measurement as 15 minute interval data (for the case of 12 months of data). The 125% factor applied to the maximum observed demand is apparently judged sufficient to cover any undercount attributable to a longer averaging interval.

Cheers, Wayne

I recall that some utilize 5 minute intervals. Some may just use 15 min intervals, same as the residential smart meters. Some may measure it in kVA? I'm unaware of a standard. In any case I agree that the notion that there's some industry standard definition of demand that's more strict and rigorous than 15min interval energy consumption has not been supported here. AHJs may need some educating, but that can always be said.

 

[infinity]

A lot of inspectors outright say that there’s no way a 100 amp service on a single-family dwelling can support a 48 amp EV charger because they’ve always seen load calculations of the dwelling being in the 80 amp range.

So when coming to them with data saying that the house is actually under 20 amp, many are just going to call BS. Having guidance from their governing body would prevent this from becoming an issue.

Read through this thread and you'll understand why HHS inspectors won't touch these demand calculations.