Apartment single phase vs three phase

[Grouch1980]

Is a 120/208 volt, single phase, 3 wire feeder more expensive than 3 phase, 4 wire? if you have a 3 phase, 4 wire feeder, wouldn't the extra phase wire offset any savings? What's everyone's experience?

Also, is a 225 amp,120/208 volt single phase panel more expensive than a 100 amp, 3 phase panel?

 

[LarryFine]

Is a 120/208 volt, single phase, 3 wire feeder more expensive than 3 phase, 4 wire? if you have a 3 phase, 4 wire feeder, wouldn't the extra phase wire offset any savings? What's everyone's experience?

The 120/208v 1ph feeder and panel are physically identical to a 120/240v feeder and panel.

The differences are line-to-line loads receive less voltage (~75% heating power) and the neutral is considered to be a current-carrying conductor.

The 3ph feeder and panel cost more, but can deliver more power for a given amperage, and is ideally suited to supply 3ph motor loads.

Also, is a 225 amp,120/208 volt single phase panel more expensive than a 100 amp, 3 phase panel?

Again, a 120/208 panel is a 120/240v panel, so is cheaper due to being common, and any 3ph panel will cost more. You would have to price 225a/1ph to 100a/3ph.

 

[Grouch1980]

The 120/208v 1ph feeder and panel are physically identical to a 120/240v feeder and panel.

The differences are line-to-line loads receive less voltage (~75% heating power) and the neutral is considered to be a current-carrying conductor.

Understood.

The 3ph feeder and panel cost more,

So for a given calculated KVA load in an apartment, a 3 phase panel and feeder will usually cost more? Vs. the 120/240 volt single phase panel and feeder.

but can deliver more power for a given amperage, and is ideally suited to supply 3ph motor loads.

Understood.

 

[MyCleveland]

So for a given calculated KVA load in an apartment, a 3 phase panel and feeder will usually cost more? Vs. the 120/240 volt single phase panel and feeder.

I believe Larry answered that,,,kVA to kVA,,,yes the 3P will be more.
Going 3P will most likely trigger in utility rate structures, meaning you will jump to a commercial rate rather than a residential rate.
Contact your local utility sales rep and he/she came clear this up for you.

 

[infinity]

We do lot's of apartment complexes and the apartment/condo feeders are all single phase. Three phase will give you 50% increase in capacity by adding a single conductor but without three phase loads there isn't much of an advantage

 

[electrofelon]

I did some Mill buildings that were converted apartments, live work studios, and shop spaces. Obviously these weren't traditional apartments so three phase was much more likely to be used. If you don't need main breaker panel boards I think the cost difference is going to be pretty minimal. There are some factors that might come into play with wiring method, wire and pipe size too if you are really trying to economize things. For example if you don't have bending equipment you would be restricted to inch and a quarter EMT - maybe that would make a difference (just an idea, didn't run any numbers). Oh one major factor might be the 83% residential derating, that would only apply to single phase correct? That would make #2 aluminum not okay for 100 amps.

 

[kwired]

We do lot's of apartment complexes and the apartment/condo feeders are all single phase. Three phase will give you 50% increase in capacity by adding a single conductor but without three phase loads there isn't much of an advantage

Large enough complex though and there is still some potential advantages of having three phase service and or major feeders, typically not enough advantage to run three phase to individual units though.

600 amp three phase @ 208 volts has similar VA ability as 900 amps single phase @ 240. POCO might rather supply you with three phase than with single phase when you get around or above this kind of load level. Price of gear and conductors starts to become even or possibly less at this sort of capacity as well. They probably don't charge at commercial rates if individual units are separately metered either. POCO would have less infrastructure and costs involved here by supplying it with a single three phase transformer than with multiple single phase transformers if that same load were divided out across multiple single phase transformers throughout the area.

 

[winnie]

I think that the approach described by kwired in post 7 is the most common for large apartment/condo installs.

You have 3 phase serving the building, and 3 phase main switchgear, but 'psingle' phase going to each meter and on to each individual unit.

-Jon

P.S. I propose 'psingle phase' as the name for 2 legs of a 3 phase system being used as if it were a true single phase center tap system.

 

[Grouch1980]

Great!... thanks everyone for your feedback.

 

[GoldDigger]

I think that the approach described by kwired in post 7 is the most common for large apartment/condo installs.

You have 3 phase serving the building, and 3 phase main switchgear, but 'psingle' phase going to each meter and on to each individual unit.

-Jon

P.S. I propose 'psingle phase' as the name for 2 legs of a 3 phase system being used as if it were a true single phase center tap system.

I like your psuggestion.

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