Determining Existing Loads

[cvirgil467]

Can a 5 minute period be used in liue of a 15 minute period for recording maximum demnd use per 220.87? I would assume a smaller window of samples is better than a larger one.

Thanks.
c

 

[Hv&Lv]

Can a 5 minute period be used in liue of a 15 minute period for recording maximum demnd use per 220.87? I would assume a smaller window of samples is better than a larger one.

Thanks.
c

No. Why do you think a smaller window would be better? Besides, why do you want to waste bits on your recording device? You already have to have 2880 readings(based on readings every 15 minutes for 30 days) you would have to take three times as many readings over the minimum 30 days.
Utility power meters(demand meters) read in 15 minute intervals. Many of the newer smart meters do also. Maybe you can just use the utilities readings.

 

[charlie b]

I think the wording of 220.87 does not allow for using 5 minute intervals, instead of 15 minute intervals. But I would not call the 5 minute sample a violation. Nor would I call it "better." Suppose that during one 15 minute period there is a very large demand that lasts for about 2 minutes. If you average that peak with the remainder of the 15 minute period, you get a smaller number. But if you instead averaged it with the remainder of a 5 minute period, the results would be a higher average. That would give you an overall higher value for "existing loads," when you look at the entire 30 day window. That is a more conservative value, and therefore would not make the next installation "less safe." But it may prevent you from adding load to a building that, in fact, does have enough spare capacity to handle the added load.

 

[steve66]

If you know the 5 min. demand, you know that the 15 min. demand can't be any higher. I would use it, even if it is conservative. I usually don't like to cut my loads that close, even with the added 25% 220.87 requires.