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Joined: Feb 2001
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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
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Joined: Jul 2004
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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.
Greg Fretwell
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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 
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Greg Fretwell
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Joined: Jun 2004
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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).
Last edited by Tesla; 05/23/12 05:10 PM.
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