300VA transformer for lighting above a ceiling

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mshields

Senior Member
Location
Boston, MA
I have a couple of incandescent fixtures for which a dedicated 277V circuit has already been pulled to (they were not originally to be fluorescent).

Anyway, the contractor has proposed putting in a 300VA transformer in lieu of pulling new 120V circuit. Seems like a good idea, but I've never done this.

What do I need for primary and seconary OCP for this small transformer?

Mike
 
mshields said:
I have a couple of incandescent fixtures for which a dedicated 277V circuit has already been pulled...the contractor has proposed putting in a 300VA transformer in lieu of pulling new 120V circuit...What do I need for primary and secondary OCP?Mike

1) 300VA is a LOT for one citrcuit worth of luminaire's. (is that right?)
2) Is there really no 208/240 panel on site already?

Stepping down 480 to 208 in commercial applications is very common but in every instance I've been involved in the secondary feeds a panel.

I think we're missing something.

Yeah I'm missing something. The K (my bad)
 
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mshields

Senior Member
Location
Boston, MA
300VA is a couple of 150W light bulbs

300VA is a couple of 150W light bulbs

From tables in Article 450 I assume if the 277V side is protected by a 15A, I can get away without secondary protection. Looks to me like all I need to do is wire it up.

Mike
 

bsh

Senior Member
secondary cable protection

secondary cable protection

If the secondary cable will exceed the limits of the tap rules (NEC 240.21(C)) then you may need secondary protection
 

RB1

Senior Member
Mike,

Where primary protection is the only protection provided, the maximum rating of the protective device is 300% unless the transformer is equipped with coordinated thermal overload protection by the manufacturer.

Ron
 

RB1

Senior Member
Because this is a two-wire, single-phase application a properly protected transformer will result in properly protected secondary conductors. Grounding on the other hand will be a challenge.
 

RB1

Senior Member
Mike,

I don't think so. Section 240.3 defers overcurrent protection of specific equipment to the respective equipment article. I don't see anything in 450.3(B) that allows for rounding up for transformer currents of less than 2 amps.

Ron
 

mshields

Senior Member
Location
Boston, MA
next higher rating

next higher rating

yeah - you're correct. If it was rated for 9amps or more, the "next higher rating" concept would apply but not for my 1Amp application. I guess I need something with a thermal overload built into it and designed for the application if such a thing exists.

Mike
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
BryanMD said:
1) 300VA is a LOT for one citrcuit worth of luminaire's. (is that right?)
I don't think so. Are you thinking 300Kva?

My turn to edit. I see you noticed.
 

benaround

Senior Member
Location
Arizona
Mike,

This is a dedicated circuit right, can you intercept it in the panel room and

divert it to a panel with 120vac, or, buy some cheap 277vac fixtures.

I just don't like it. JMO.
 
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