Transformer

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Benton

Senior Member
Location
Louisiana
Yesterday my boss, another electrician, and myself went out to our companies parking lot to get an idea of what to do on an upcoming job.
We are just installing a 120V circuit for a projector (580w) that is going to be used outside to display an image on the side of one the buildings. The closes receptacle is about 50-60 yards away. I suggested that we use it. The other electrician recommended buying a small transformer to step down the voltage form a pole light-277V. We bought the transformer, but I have doubts about its functionality. It is a Jefferson Electric tranformer, the secondary side has a time delay fuse. I know that we will get 120v, but it seems to me that this type of tranformer should be used for control purposes. Am I over concerned?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
The transformer doesn't care what the load is...only how much load there is. Don't forget that this is a separately derived system and will require a grounding electrode for the secondary side.
 

augie47

Moderator
Staff member
Location
Tennessee
The transformer doesn't care what the load is...only how much load there is. Don't forget that this is a separately derived system and will require a grounding electrode for the secondary side.
Before you get carried away on electrodes, check Exception to 250.30(A)(3). Based on your load your transformer might fit the criteria.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Engineer
The different types of transformer like power, control, or even doorbell are primarily not much more than marketing terms. As far as the NEC, and manufacturer testing, they can be used interchangeably.

Yes there are some construction differences such as enclosure, or lack of, and some performance issues (i.e control power transformers have very reasonable voltage regulation while doorbell ones have relatively poor regulation at no load). But in general, all a transformer cares about is the amount of its loading.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
His load is only 580 va. Under exception 3 is it nor possible to use the geounded enclosure as his electrode if the VA is less than 1000 ?
I don't see this as being an Article 725 Class 1, 2 or 3 circuit so the exception would not apply. I think this is a power circuit, a small one, but still a power circuit.
 

augie47

Moderator
Staff member
Location
Tennessee
I don't see this as being an Article 725 Class 1, 2 or 3 circuit so the exception would not apply. I think this is a power circuit, a small one, but still a power circuit.
I debated that for a long time...they could, IMHO, do a bit better in Art 725, but I believe you are correct.
 
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