480 volt single phase lighting problem

Thread Starter


Joined Dec 17, 2010
I happened to hear this mentioned about some 480 volt lighting that is being installed. There are two legs left of three phase 480 volt system that will energize the single phase 480 volt lighting. An apprentice was told that if one of the two phases was lost,for example if one of the breakers tripped,half the lights would still work. Someone else said none would work. Who is correct? and would you explain the theory?


Joined Feb 4, 2008
So, you are saying that two phases are used to power the lights (no neutral), aren't you?

If this is the case, then all the lights will go off if one breaker trips.


Joined Oct 27, 2010
if its a 3 phase system and they are fused individually then that is correct.

ie if L1 tripped L2 would still function.

are they are on a contactor?


Joined Jul 26, 2010
I can't say that I've ever heard of 480V lighting, in practice they usually use one phase leg which would be 277V to neutral.

My guess is that you've got 277V and they split half of it off one leg of the 480Y and the other half from another one.


Joined Aug 30, 2007
I can't say that I've ever heard of 480V lighting
Some of the newer High pressure sodium, metal halide, ballasts come with multiple taps. One of the available voltages is 480v. I agree with what you say about the 277v scenario, that would explain the OP question.


Joined Jul 26, 2010
To get 480V you'd have to run two live phases of (common to the US) power to them and that would defeat the purpose of saving copper on the long runs usually associated with large area lighting. You'd also want to run a neutral along with the normal grounding these fixtures would have. Can't say as I've looked at the new code on that possible scenario but I'll bet a neutral would have to be included.

In other words it would be economically unfeasible to deviate from the 277V standards we already have in place.

HID lighting is on the way out, we're upgrading our entire warehouse areas to new 277V CFLs that screw right into the mogul base sockets, all you have to do is bypass or remove the conventional HID ballasts. They've got CFLs that only take 105W from a 277V line that put out almost as much light as a conventional 400 W MH or Pulse start HPS lamp that take almost 500W each to operate but it's a more pure 4,100*K so nobody notices the difference.