3 phase system , single phase equipment

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wireperson

Senior Member
Location
Florida
this is a 120/240 wye 3 phase fed building. they want to install 4 split AC systems . 5 ton (cu), 10kw heater (ahu) each . the question is is it ok and is there any pros and cons of using single phase HVAC systems fed by 3 phase system?.Its a comercial building and the units they want to buy are for residential use.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
wireperson said:
this is a 120/240 wye 3 phase fed building. they want to install 4 split AC systems . 5 ton (cu), 10kw heater (ahu) each . the question is is it ok and is there any pros and cons of using single phase HVAC systems fed by 3 phase system?.Its a comercial building and the units they want to buy are for residential use.

Bad idea in my opinion but it can be done but you have to watch and make sure you can balance the load.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
wireperson said:
this is a 120/240 wye 3 phase fed building.

No such beast. You can have a _delta_ service with both 120 and 240 available, and you can have a _wye_ service that has 120 and 208V, or a wye service that has 139V and 240V.

If delta, then it may be designed primarily for 120/240V single phase service, with a three phase 'stinger' added for the few three phase loads, or it may be designed primarily for 240V three phase service, with a center tap added to serve the few 120V loads.

You need to know exactly what you have before you can really decide if it is reasonable to add these loads.

-Jon
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
First be sure they are rated at 208 and not 240
then place them so 3 are equaly loaded on 3 phase 1 and 3 ,5 and 7,9and 11 the other should be on legs that are normally low.Really bad design but might be cheaper on them and you.
 

charlie

Senior Member
Location
Indianapolis
Dennis Alwon said:
Bad idea in my opinion . . .
I agree with Dennis. 3? equipment will not have a need for starting capacitors, starting windings, a centrifugal switch, or other 1? "stuff" to go bad. On top of that, 3? motors and compressors are less expensive than 1? because of all the starting "stuff". I would think the owner would have priced the equipment and would be also be aware that the long term maintenance costs will be higher. :confused:
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
charlie said:
I agree with Dennis. 3? equipment will not have a need for starting capacitors, starting windings, a centrifugal switch, or other 1? "stuff" to go bad. On top of that, 3? motors and compressors are less expensive than 1? because of all the starting "stuff". I would think the owner would have priced the equipment and would be also be aware that the long term maintenance costs will be higher. :confused:
5 ton units will not be cheaper,and the disconnects will be far more costly than a $10 pull out.Breakers also more costly.When looking at price look at total cost of all trades.

keeping the load balanced will not be easy as they wont all run at same time but they are small
 
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