looking for trick to balance single phase load across three phases

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BrianMuir

Member
Location
Comox BC
I have a problem where I have a single phase 208V load going into a service location, which has adequate capacity in terms of overall KVA, but my calculations indicate that the two involved phases could be overloaded (based on utility company record of historical load).

I believe it is necessary to either reconfigure the load as three phase, (the client is reluctant to consider this), upgrade the switchgear (also not easy), or take power from an alternate location, which we do have at this site, but a fair distance away (= big expensive conductors).

A transformer that balances a single phase load across multiple phases would do the trick, but I don't think such a beastie exists.

Am I missing any possible solutions?
thanks
 
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wirenut601

Member
Location
champaign, illinois
phase loads

phase loads

iwire is correct just take amp readings of all your single phase loads and due the math. move circuits around to different phases so you get a fairly even load between all three phases.
 
PetrosA

PetrosA

Senior Member
Location
Lancaster, Pennsylvania
I'm not sure your configuration is coming across accurately - are you dealing with a panel that has two hots and a neutral pulled (single phase configuration) from a three phase service (120/208)? If so, you could have issues with overloading those two phases and you will have problems with the neutral as well, since balanced loads on the two hots won't cancel each other like a 240V load on a single phase neutral will. I'd pull the third phase and upgrade the switchgear to a new three phase panel. That's the only way to really make things copacetic.
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
It sounds to me like his new load is indeed single phase line to line.

But is also sounds like the panel has existing loads and there is a good chance that some of the existing loads are single phase L to L or single phase L to N. Either way you could push those existing loads around to lighten the load on the two phases you want to use for the new load.

Of course if all existing loads are three phase my suggestion is worthless. :)
 
kwired

kwired

Electron manager
Location
NE Nebraska
A transformer that balances a single phase load across multiple phases would do the trick, but I don't think such a beastie exists.
Click to expand...

The only way that comes to mind to me on how to do that is to rectify the input to DC then invert it back to single phase AC. There are probably easier and less expensive alternatives unless you have a single load that can not be subdivided across multiple phases.
 
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BrianMuir

Member
Location
Comox BC
thank you.
The project involves an expansion to a school. The existing loads consist of 4 three phase panels, all well balanced. The major portion of that load is all the three phase mechanical/heating equipment.

The load to be added is a prebuilt modular classroom, which unfortunately is designed as a single phase component. The main portion of this new demand is a heat pump, 208V 17KVA, 1 phase.

I think my best move is to ask the client to swap the new heat pump with an equivalent three phase module, and then have our contractor reconfigure the classroom as a three phase unit.
 
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Besoeker

Besoeker

Senior Member
Location
UK
friendlyfire said:
thank you.
The project involves an expansion to a school. The existing loads consist of 4 three phase panels, all well balanced. The major portion of that load is all the three phase mechanical/heating equipment.

The load to be added is a prebuilt modular classroom, which unfortunately is designed as a single phase component. The main portion of this new demand is a heat pump, 208V 17KVA, 1 phase.

I think my best move is to ask the client to swap the new heat pump with an equivalent three phase module, and then have our contractor reconfigure the classroom as a three phase unit.
Click to expand...
Sounds sensible.
 
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