Voltage drop on 277v lights in 480 system

[SparkyDave1990]

Hey guys,

First time posting so take it easy on me. My question involves the voltage drop equation. My boss put me in charge of the lighting and I don't wanna screw up the first thing he puts me in charge of.

I'm working warehouse lighting with 277v lighting on a 3 phase 480 volt panel. Each light draws about 0.5 amps and the furthest one is approximately 400' away from the panel. I'm running it in steel conduit and until it splits off it will be all 3 phases along with the neutral and ground in the same pipe.

My question is what do I use for the amperage value and voltage value for the voltage drop calculation to see if I need to upside the wire? Do I use 20a be a use that's the size breaker it's going on or the .5a for the current the fixture draws. There are 8 on each circuit. Do I use 277v or 480 because it's a single phase circuit on a 3 phase system?

 

[Fitzdrew516]

Hey guys,

First time posting so take it easy on me. My question involves the voltage drop equation. My boss put me in charge of the lighting and I don't wanna screw up the first thing he puts me in charge of.

I'm working warehouse lighting with 277v lighting on a 3 phase 480 volt panel. Each light draws about 0.5 amps and the furthest one is approximately 400' away from the panel. I'm running it in steel conduit and until it splits off it will be all 3 phases along with the neutral and ground in the same pipe.

My question is what do I use for the amperage value and voltage value for the voltage drop calculation to see if I need to upside the wire? Do I use 20a be a use that's the size breaker it's going on or the .5a for the current the fixture draws. There are 8 on each circuit. Do I use 277v or 480 because it's a single phase circuit on a 3 phase system?

A lot of this is hard to explain without drawings, but I digress. It really depends on how you want to do it. If it's site lighting, or long enough runs where it makes sense often you can do a series voltage drop where you calculate the load at that particular point in the circuit and you size the wire for each run in between each light (each run being a different load). However, the more standard way to do voltage drop calcs for indoor lighting is to do them on a per circuit basis. In other words - calculate the load on the whole circuit and size the circuit's wire to that, it sounds like this is the method you should be using. If your voltage is 277v that's what you use. If the longest run is 400' out with 277V, 4A (8 fixtures) then you shouldn't need to upsize as #12's (Copper) will be under 3% VD.