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#110831 - 07/14/06 09:29 PM C.T. Cabinet Shorted  
Admin  Offline

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Member
Joined: Oct 2000
Posts: 3,437
NY, USA
Quote
This is a C.T. cabinet and the electrician decided to use some old terminal lugs instead of splice blocks to connect the wires and save some money. It looked neat and I almost approved it until I studied it further because something just didn't look right. Gut feeling or instinct. Then it dawned on me. The lugs were screwed to the plywood backboard with long wood screws. Long enough to penetrate all the way through the wood to the metal cabinet. If I had allowed it to be energized it would have flashed over behind the wood.

(Note; The local utility requires the wood backboard. I don't like it but, can't make them change.)

Alan Nadon
[Linked Image]


2017 / 2014 NEC & Related Books and Study Guides

#110832 - 07/15/06 12:28 AM Re: C.T. Cabinet Shorted  
napervillesoundtech  Offline
Member
Joined: Feb 2006
Posts: 144
Naperville, IL, USA
The utility *requires* this?!? That seems rather odd.


#110833 - 07/15/06 07:00 AM Re: C.T. Cabinet Shorted  
RODALCO  Offline
Member
Joined: Dec 2005
Posts: 854
Titirangi, Akld, New Zealand
Strange that the utility allowes the extra fire danger.
In NZ the CT cabinets are from steel, The bussections or blocks are mounted on insulated stand offs.
A PVC cover is fitted to cover the exposed bare copper terminals, underneath the CT chamber door to avoid direct touch contact to exposed live conductors.


The product of rotation, excitation and flux produces electricty.

#110834 - 07/15/06 12:27 PM Re: C.T. Cabinet Shorted  
Alan Nadon  Offline
Member
Joined: Mar 2005
Posts: 399
Elkhart, IN. USA
Utility requires the wood back to make it easier for them to mount different size current transformers. Listed CT enclosures are required to provide adjustable mounting brakets and to pass an ice test. This cabinet and others like it are listed only as junction boxes, not CT enclosures. For years the utility supplied them and they were utility property. Now with deregulation the contractor has to supply them but, this is the only style they will accept.
They have worked for years and I don't feel up to a fight with the utility company. [Linked Image]
Alan--
As Kenny Rogers sings: "Sometimes you hold 'em, sometimes you fold 'em, sometimes you walk away..."


Alan--
If it was easy, anyone could do it.

#110835 - 07/15/06 12:33 PM Re: C.T. Cabinet Shorted  
LarryC  Offline
Member
Joined: Jul 2004
Posts: 781
Winchester, NH, US
I am not an electrician, but I have an interest in becoming one.

Why is there such a difference in the wire sizes for the incoming service and the load?

LarryC


#110836 - 07/15/06 03:45 PM Re: C.T. Cabinet Shorted  
mamills  Offline
Member
Joined: Nov 2001
Posts: 745
Wharton, Texas, USA
The wood screws for the lugs not withstanding, it looks like the two hot legs are double-lugged.

Isn't some type of bonding supposed to take place in here?

I may be missing something obvious, but which side is line and load?

Mike (mamills)


#110837 - 07/15/06 06:40 PM Re: C.T. Cabinet Shorted  
John Crighton  Offline
Member
Joined: May 2005
Posts: 177
Southern California
Mike, I think if you look closely, it's not double-lugged. The center wire has its own hole, right in the middle and underneath the other two. The middle setscrew is to the right of the others.

I'm not sure, but I think I see the enclosure bond at the bottom left. Either that, or the EGC is just lying loose! The conduits are probably RNC, so no bonding nuts.

I'll guess that the larger wires are the load, that they've been beefed up to reduce voltage drop on a long run, and that they go to two separate load centers. (Am I close?)

Alan, suppose those lugs had been bolted to a separate plate of plywood, then screwed as an assembly to the backboard. There'd be a full thickness of plywood between live parts and the enclosure. Would you have accepted it then?


#110838 - 07/15/06 11:19 PM Re: C.T. Cabinet Shorted  
mxslick  Offline
Member
Joined: Oct 2004
Posts: 803
Atomic City, ID USA
Quote
Alan, suppose those lugs had been bolted to a separate plate of plywood, then screwed as an assembly to the backboard. There'd be a full thickness of plywood between live parts and the enclosure. Would you have accepted it then?


Don't know for sure how Alan would feel, but I would not. It would still be possible, given enough moisture buildup in or on the plywood to form a conductive path, with heating, arcing or a flashover possible.

Painting the wood won't help either as some paint is at least semiconductive.

edited to fix a missing word..

[This message has been edited by mxslick (edited 07-15-2006).]


Stupid should be painful.

#110839 - 07/16/06 12:22 PM Re: C.T. Cabinet Shorted  
Alan Nadon  Offline
Member
Joined: Mar 2005
Posts: 399
Elkhart, IN. USA
LarryC: Electricain has to size wire to the NEC. Utility co sizes their wire to expected load. If their wire fails they replace it. Until then they save money.
John: You're right all the lugs had three openings.
Conductor with green tape is a bond and then goes to the ground rod. Although the six screws through the plywood on the grounded phase made an effective bond although unintended. [Linked Image]
Conduits are non-metallic.
If I remember right parallel conductors went to a single panel, located just inside the wall.
Alan--


Alan--
If it was easy, anyone could do it.

#110840 - 07/16/06 07:57 PM Re: C.T. Cabinet Shorted  
tdhorne  Offline
Member
Joined: Mar 2001
Posts: 345
Maryland, USA
Does the utility in question require fire treated plywood for these improvised CT cabinets.

There is a very nice insulated lug made by Polaris Connectors that would be perfect for that application. http://www.polarisconnectors.com/37022_POLSAL_EXTRA_IPLMD1.pdf
It has insulated mounting holes in each end to hold it in place. Is that what you meant by the term splice blocks?
--
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use." Thomas Alva Edison

[This message has been edited by tdhorne (edited 07-16-2006).]


Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use" Thomas Alva Edison

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