The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!

Featured Items:

Switch Bit - Interchangeable Flex Bit System
>> Switch Bit -
Interchangeable Flex Bit System

>> 2014 NEC and Related

Recent Posts
long & crawford switchgear ring main unit 11KV 400
by willmesa
Today at 04:29 PM
Satec power meter CT wiring
by sedesigner1
Yesterday at 07:05 AM
Just gotta Say
by Webmaster
07/21/14 08:40 AM
Overhead Span Across Portable Garage.
by wewire2
07/21/14 08:37 AM
Minimum Bend Radius?
by HotLine1
07/17/14 06:47 PM
New in the Gallery:
Copper Theft
Shout Box

Top Posters (30 Days)
HotLine1 34
Tesla 18
gfretwell 15
renosteinke 11
sedesigner1 8
Who's Online
0 registered (), 114 Guests and 4 Spiders online.
Key: Admin, Global Mod, Mod
Topic Options
Rate This Topic
#206106 - 05/22/12 03:45 PM 450.3(C)
Steve T Offline
Member

Registered: 02/14/01
Posts: 312
Loc: Oak Park, IL, USA
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

Top
2014 / 2011 NEC & Related Books and Study Guides
#206107 - 05/22/12 04:13 PM Re: 450.3(C) [Re: Steve T]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 8356
Loc: Estero,Fl,usa
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

Top
#206109 - 05/22/12 04:41 PM Re: 450.3(C) [Re: gfretwell]
Steve T Offline
Member

Registered: 02/14/01
Posts: 312
Loc: Oak Park, IL, USA
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 smile

Top
#206111 - 05/22/12 08:32 PM Re: 450.3(C) [Re: Steve T]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 8356
Loc: Estero,Fl,usa
I found this article that has some info on them

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

Top
#206116 - 05/23/12 03:07 PM Re: 450.3(C) [Re: Steve T]
Tesla Offline
Member

Registered: 06/16/04
Posts: 1173
Loc: Sacramento, CA
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.

-----

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).






Edited by Tesla (05/23/12 03:10 PM)
_________________________
Tesla

Top



ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals