I currently have a tower crane that the general put 277 volt lights on and the crane is fed 480 volt 3-phase. I installed and 7.5 Kva transformer on it for 120v/208 power. I am trying to figure the best way to utilize one or two legs of the 480v available because I do get 277V to ground on it and have this be safe would an auto transformer be it I believe it would be 6.8 Kva load each light is 4.1 amps at 277V there are 6.

 

just hook them to ground and one or both legs of the 480. if you have 6 lamps, put three on one leg and three on the other, to maintain balance. of course, use the usual disconnect, fuses and such.

 

Is the 480 power to your crane Wye connected ? That would mean it has a neutral plus the 3 phases, 4 wires total, not including ground. The ground should never be used as a current carrying conductor, it's a code violation. I'm not really clear on what you want to do with the transformer.

 

and a crane should never not have a pulled ground. none of our cranes here have only 2 phases, all are three phase with ground. 4 wires through the shoes tothe feed rails.

 

and a crane should never not have a pulled ground. none of our cranes here have only 2 phases, all are three phase with ground. 4 wires through the shoes tothe feed rails.

They dropped a 4-wire SO 3 hots and a ground. This is just a temporary construction tower crane. I got the lights on and everything seems good since it is only accessible to qualified personnel and grounds will not be broken I am going with it

 

In most areas a 4 wire 277/480 three phase systems with one wire sharing both common and ground duty is legal so if its allowed in your area that how I would go about it and never give it a second thought.

 

Could be installed between two phases or I am wrong?

 

Voltage between 2 phases would be 480