Single Vs. Three Phase (Condo)

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Npstewart

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Im working on a new condo building with several units. On average, a typical demand load per unit is about 28kW and the voltage is 208v coming into the building. These are condos and therefore are subject to change and I would like to leave some capacity for future alterations. Im trying to figure out if it would make more sense / cost effective to bring single phase (or) three phase to the individual dwelling units. These will be fed from a meter center with three phase in, and then three or single phase out depending on conclusion.

So....

28kW @ 208/1 = 135 Amps and I would probably use a 200A service for this because 15 amps of spare capacity (3.1kW) is too close for comfort.

28kW @ 208/3 = 78 Amps and I would probably use a 100A service for this because 22 amps of spare capacity (8kW) is good for spare capacity.



Given all that, do you think it would be more cost effective to use a 200A service @ 208/1 (or) a 100A service @ 208/3? I feel like 3-phase is a better option here due to needing some spare capacity.

Thanks!
 
I have contemplated this before with condo/loft type spaces. I think the cost for the feeders and condo panels is going to be about the same either way. You may want to investigate the meter centers and feeder breakers as I could see a price jump there to go with three phase - although with single you are into 200A frame stuff, where with 3 you could use a standard 3100 feeder breaker, so I don't know. Price it out
 
One sorta nitpicky thing I wanted to comment on:. I don't like the term "demand load". I don't really know what that means. If it is an article 220 load calculation, I would call it "calculated load.". The term "demand" to me makes me think of 220.86 where you have historically measured the average 15 minute (usually) interval load,
and selected the highest interval in a month (usually).
 
electrofelon said:
One sorta nitpicky thing I wanted to comment on:. I don't like the term "demand load". I don't really know what that means. If it is an article 220 load calculation, I would call it "calculated load.". The term "demand" to me makes me think of 220.86 where you have historically measured the average 15 minute (usually) interval load,
and selected the highest interval in a month (usually).
Click to expand...

Interesting take. I normally view the load for dwelling units as being either “demand” or “connected”. When I say demand, I just mean the load after the permitted diversity/ demand factors have been applied. I’ve never really looked up to see if there was an actual definition.


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I have a hard time believing a 3ph 100a service would give you enough headroom for any kind of real add-on if you're already calculated at 78 amps. What are you gonna do with 22 amps of 3phase power? Nothing, really.

There's no way you would ever add enough lights or receptacles to take up that much.

I can't imagine any future alterations that would add more than a couple of amps, unless it was more cooking equipment, sauna, or something else along those lines

200 amps of single phase would be the only way to leave enough headroom to really matter.
 
I presume that these are residential condos and that most of the load is L-L.

If you only have L-L loading a 100A 120/208V 'single phase' supplies 20.8 kVA as expected. But if only L-N loading it can supply 24 kVA. Remember you have two 120V 100A legs.

I know this is a small thing, but it might be relevant in terms of headroom for future expansion.

Jon
 
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