480/277V step down

Status
Not open for further replies.
S

solis

Member
We are replacing lamps, ballasts and sockets in a parking lot. We are replacing 1000W MH with a newer, lower wattage lamp/ballast. The site voltage is 480, but the manufacturer only makes a 277V ballast and is sending a step down transformer to mount at each fixture. I feel the transformer is not rated high enough, that it needs to be 125% of the each lamp/ballast load. He says he does this all the time (hope not). Am I wrong code wise? I couldn't find the exact code reference that would say this. I found the overcurrent section. Somewhere in the back of my mind I remember you could load a trans. 100% but don't really use them in the work I do. I couldn't find the exact code reference that would say this. I found the overcurrent requirements.
Thanks
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Transformers are not required to be rated 125% of the load.

You can load a transformer to 100% of its nameplate.

Other questions come up such as grounding and bonding though.
 
S

SceneryDriver

Senior Member
Location
NJ
Occupation
Electrical and Automation Designer
J

JFletcher

Senior Member
Location
Williamsburg, VA
Yep, those. Most problems from 480-277 or 277-480 involve remarking the grounded conductor. Leaving everything 480 to the pole and using the autoxfmr to get 277 solves that frequent problem, tho I'd still prefer line voltage LED w/o a xfmr to fail at some point.
 
Electric-Light

Electric-Light

Senior Member
SceneryDriver said:
Use of an autotransformer would pretty much solve the grounding issues, yes? GE makes something specifically for the purpose: http://www.gelighting.com/LightingW...p-Down_Transformer_SellSheet_tcm201-20992.pdf



SceneryDriver
Click to expand...

solis said:
Exactly the one we are using.
Click to expand...

JFletcher said:
Yep, those. Most problems from 480-277 or 277-480 involve remarking the grounded conductor. Leaving everything 480 to the pole and using the autoxfmr to get 277 solves that frequent problem, tho I'd still prefer line voltage LED w/o a xfmr to fail at some point.
Click to expand...

You can only use that transformer under limited conditions. You should also assign transformer loss to the LED ballast as if it's part of the luminaire.

Wye 480V – Connect any two phase wires to input of transformer. (this is when you have 480/277 but neutral isn't pulled to the poles)
Delta 480V – Special consideration, connect to ground referenced legs only
Ungrounded – Not suitable for electronic systems & GE step down transformer
 
Status
Not open for further replies.
Top