277 or 480

[jibron]

I have 480/277 3 phase available.
Is it ultimately better/cheaper to run my floods at 480 single phase as opposed to 277 or is it just a matter of being able to use smaller wire, smaller conduit , etc?

 

[peter d]

Depends on a variety of factors -distance, availability of 480 volt fixtures, number of fixtures per circuit, wiring method, etc.

 

[jibron]

I'm talking from a cost of operation standpoint.
AND ALSO
I'm confusing myself terribly using my voltage drop calculator.
I'm trying to figure voltage drop and total load to size my 480v 3 phase breaker.
I have six 1000w MH multi-tap fixtures.
I'm powering them through one 3 phase breaker from a 480/277 panel.
How would the size of the breaker change if I were to:
run 2 fixtures off each phase to neutral @ 277V?
or
run all the fixtures at 480V off 1 breaker?
any opinions on the better route?
p.s.(the breaker will feed a three pole fused disconnect immediately before the installation.)
The furthest fixture is 500' from the panel, the nearest is about 300'
Specs say 2.4A @ 480v and 4.1A @ 277v

 

[augie47]

There is no difference from a cost of operation standpoint, kw is kw.
With 3 phase avaialble, if you operate 2 fixtures per phase, it will make little difference if you use 480 or 277. In either case you could use a 15 amp breaker.
The worst case scenerio, at 277, with 2 fixtures 500 ft away and a #12 wire your voltage drop would be less tha 5%

 

[kingpb]

You will have 2000W on each of ph A, B, C regardless of whether you use 480V, 1ph, or 277V, the load will be balanced either way.

Sounds like voltage drop may be the deciding factor. Voltage drop is predominantly I^2R losses, so operating at the lower current will reduce your losses.