Load Calcs for Receptacles

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whisperinghill

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I have a question on performing load calcs for receptacles in a non-dwelling building.

Here is my issue. At my facility we have field produced power poles with an example of (4) Single 5-20R 120v 20A and (1) L5-30R 120v 30 A and (2) L6-30R 208v 30A receptacles, all are individually fed and all receptacles are mounted in about 18"- 24" of power pole.

At some time some, none or all of these receptacles on this pole could be in-use.

Technically this is a multi-outlet assembly, correct? So if I used 220.14(H) then the demand factor would be around 300va since they would most likely be used simultaneously. Well that doesn't make sense.

NFPA Art 220.44 states receptacles loads calculated from 220.14(H) and (I) shall be permitted to use tables 220.42 and 220.44 to calculate demand factors. So if I use 220.44 then the first 10kva is at 100% and the remaining at 50% demand factor.

So if I add my loads , 120v x 20a x 4 recps = 9600 va and then 120v x 30a 2 recep = 3600va and then 208 x 30 x 2 recps = 12480va. Now part of this is 208v load. Or I could use the 80% loading rule for continuous loads.
What is the first 10kva? To me each receptacle is the first 10kva so all would be at 100% demand factor.

We use excel spreadsheets for our panel schedules.
We include connected amps per phase for each circuit. and an estimated demand for those that do not have dedicated loads.

Since my 120v 20a receps are not general purpose wall receptacles, using the 180va load or 1.5a is not practical or realistic.

Nor is it realistic to use 100% demand factor for each receptacle. this would give you a full panel with a third of the breakers connected.

Using a single snapshot of the load is also not realistic, because all of these could be zero amps or at 18 amps, etc.

What is a realistic way to calculate the demand factor for these receptacles? Be conscious that I may have every circuit on a 150A panel fully connected to receps on power poles but then only draw 10 amps per phase or draw 80a per phase.

I appreciate any help someone could provide.

perplexed!
 
I would be inclined to look at this from a practical point of view first, forgetting for the moment the "correct" way to calculate the load for NEC purposes.

What is the maximum load you are likely to see when as many things are plugged in and drawing power as are ever likely to draw power simultaneously?

That with a safety factor for future unknowns will tell you what you really need. If that exceeds the NEC calculated load, go with what you know is actually needed versus what you calculate.

It does you no good to spend a lot of time trying to downsize things and end up with something that trips a main now and then.
 
To add to what petersonra said, I believe this is a great example of where the code will allow a person to undersize a system. We must remember that the code is a minimum standard. This is why I always look first at what is needed practically before I test it with the code. If my design meets the minimum requirements of the code, then fine. If not, then time to up-size to the code required minimum.
 
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