ECN Forum Forums Code Related Discussion NEC & other Code issues 450.3(C)

Since 450.3 says "Overcurrent protection...comply with...(A), (B), or (C).", if I am providing overcurrent protection per (B), then I am not required to provide primary fuse protection for my indoor voltage transformer, correct?

If I choose to only follow (C), I can pick any size fuse I want because there is no reference to a table in (C), correct?

Or should 450.3 read "...(A) or (B) and (C)? What's the intent?

Thanks,

Steve T

A "voltage transformer" is not a power transformer.
It is a precision transformer used in protective relay systems. Different deal altogether.
For power transformers you are either 450.3 A or B depending on voltage.

I agree they could have a more informative FPN here.

Thanks Greg. That sounds right based on the FPN, but without any explicit definitions, a search for 'voltage transformer' on the net brings up a lot of stuff. Anyone have the original substantiation on this section? Or a link to a manuf. web site that shows a voltage transformer as intended in the code section? Thanks again. An Engineer is going to be happy

I found this article that has some info on them

http://www.geindustrial.com/pm/notes/artsci/art08.pdf

Class 450.3 (A) = OVER 600 Volts...

So forget it. That's industrial territory.

Class 450.3 (B) = LESS THAN 600 Volts...

This is the category for dry-type transformers we all know and love.

Class 450.3 (C) = Voltage Transformers...

Which is what you've described it as.

EITHER WAY you're required to provide OCPDs...

See 408.52: "...is protected by standard overcurrent devices rated 15 amperes or less."

So, you don't get to pick a rating out of the air.

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BTW, I don't think that your transformers are 450.3(C) Voltage Transformers. I'll bet that they are a part of some low voltage lighting set-up.

That makes them 450.3(B) transformers, in my eyes.

Why? They're not switchboard devices with potential coils, pilot lights, etc.

They're power supplies for some low voltage loads. -- Hence 450.3(B).