using a 3phase service for single-phase units is ok?

D

davidsol

Member
Location
california
Occupation
electrical engineer
I have 12 units project that has a 3ph elevator, so we need a 3phase service.
is that ok too use that 3phase service for units? my units use single-phase
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Yes, it's very common to use a three phase service and single phase for each unit.

Welcome to the Forum. :)
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
You do need to confirm the voltages on the 3 phase service. It is possible POCO will provide a 120/240 delta in which case the B phase would be 208 v to ground which would effect your using it on the single phase loads. It is also possible the 3 phase will be 208/120 which will have a effect o 240v loads.
 
kwired

kwired

Electron manager
Location
NE Nebraska
If this is multifamily then it may be pretty common to see 208/120 three phase service, three phase for the "house panel" which likely also includes the elevator but just two lines and neutral for each tenant panel as they won't have any three phase loads in them. They stagger these singlep phase feeds to the units connections to balance load on the service. Keep in mind that 240 volt resistance heaters (or appliances with resistance heat elements) will still work but will only put out approximately 75% of their 240 volt rating. Usually is not a problem unless unit selection was minimal to begin with. Air conditioners/heat pumps are all pretty much designed to run on 208 or 240 nominal. They will just draw a little more @ 208 then @ 240. Nameplate values still are what you size conductors and OCPD to, not many have dual values on nameplate though.
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
One would think that if this is a new design the equipment specified would be 208 volts if the service were 208Y/120.
 
kwired

kwired

Electron manager
Location
NE Nebraska
infinity said:
One would think that if this is a new design the equipment specified would be 208 volts if the service were 208Y/120.
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Or whoever selects units knows to upsize certain items like water heaters or space heaters. Ranges/clothes dryers, you generally just going to have longer run time to do same task. You possibly can get a 208 volt rated water heater or space heater but more common is dual rating marked on the units and you need to know how to select accordingly to supply volts.
 
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