ECN Forum Forums Photo Discussion Forums Violation Photo Forum C.T. Cabinet Shorted

The utility *requires* this?!? That seems rather odd.

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.

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.
Alan--
As Kenny Rogers sings: "Sometimes you hold 'em, sometimes you fold 'em, sometimes you walk away..."

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

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)

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?

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).]

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.
Conduits are non-metallic.
If I remember right parallel conductors went to a single panel, located just inside the wall.
Alan--

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).]

People really use wood for this....no insulation between the plywood and the lugs?? No way!!!

All wood has some moisture in it. This varies with the environment over time. The stuff (chemicals, salts, blah, blah) in the wood allows it to conduct electricity right. It's just a question of how much current flows.

If I did this in an industrial control cabinet the inspector would ask me what I was smoking....Convenience should be no excuse by the poco over a safe installation. Dang!!

Do ya suppose if the poco started following some type of electrical code that our rates with triple?
Good...Fast...Cheap; pick two.

RSlater,
RSmike

Ok then, It would have made sense if those parallel conductors were to account for VD in a long run, but with the panel being just on the other side of the wall, am I missing something?

How about plexyglassfor the back and then another half plexyglass with spacesrs, over the lugs?

Jeepmudman:

First off, welcome to ECN!

Plexi might be o.k., certainly a better insulator than wood, but if I was the AHJ, I'd still fail it. Plexi is sensitive to temperature and would readily deform/melt if the lugs got too warm. Now as to a plexi cover that would be o.k. as long as it was not in direct contact with the lugs.

In general:

An issue that I have now noticed and no one's questioned: Aren't the parallel conductors all supposed to be the same length? (Not only each phase/neutral, but the overall set.) From the looks of this install, I'd say no. Another red sticker?

It also makes no economic sense either, for if the panel is just the opposite side of this cabinet, wouldn't a single run of the proper conductor size cost less than the two runs installed?

Alan:
We use a listed/labeled UTILITY Approved CT cabinet, most are NEMA3R. 800 amp rated.
Interior is setup to the UTILITY specs, with brackets, etc for support of CT's. Some CT's are 'bar type, four stud mounted to cabinet rail, and landing pads for line/load lugs. Some are 'donut type', with mounting base to match cabinet brackets.

PSE&G requires non-magnetic, 1/2" dia., stainless bolts, nuts, flat washers, and belleville washers. Utility Wiring Inspector checks hardware with magnet.

Larger (over 800 to 1200 amp) CT cabs are special order fabricated to Utility specs, basically a larger version of the above.

NONE have any wood. No grounding/Bonding conductors are allowed within the CT cabinet, bonding lug is on exterior, IF neutral conductor is not present.

Kenny also said....'know when to RUN'

John

luke,

secondary wiring (customer wiring) is sized as per table 310.16. paralleling has nothing to do with VD.

thank you for the welcome :MXSLICK. This is a great place.

jeepmudman,
Welcome mate!,

Only conductors actually electrically in parallel need to be of the same length, diameter, insulation and conductor material. Separate phases (or the neutral) could be of different characteristics. The neutral could be smaller, shorter, etc. Phase A could be copper and Phase B aluminium, etc. But all conductors of Phase A need to be the same, etc.

-Jon

Here in the city of Austin Tx, we do not allow any splicing of the main conductors going through window ct's in any ct box; must be pulled through in one piece.
Also we don't allow bare energized lugs mounted on wood-an instant red tag.
B. Parks

Alan,
I'm not sure I understand. One end of the conductor is bonded to the cabinet and the other end goes to the ground rod? Where is it bonded to the neutral? What is the fault current path?

I'm with eprice.

Soooo...., how is the fault current going to ground? Where is the bonding to the neutral? If it's in another feeder panel before the the CT panel well then, O.K. maybe but....?

I'm missing something here aren't I?

The grounding electrode conductor can be bonded to the neutral in the panel.

Here in So CA, The GEC is not permitted to even pass through a utility CT cabinet, nor be bonded there.

Grounding / bonding conductor starts at the service disconnect, goes to the CT (bond) then continues to the ground rod. (grounding)
CT cabinets must be bonded per 250.66 if the conduits are non metalic.
Conductors are frequently paralleled to make it easier to pull. 1,500 KcMil (625 A) or 2x 350 KcMil (2x310A=620A) or 4x 1/0 (4x150A=600A) And to Save Money, and our natural resources.
For a 600 amp service the conductors listed above will all handle the load. Using seperate conduits runs where needed to avoid derating four runs of 1/0 will be a lot less expensive than one run of 1,500 KcMil if you can even find it. Then try to install it.
Alan--

Utility requirement or not. There is no way that would pass in this jurisdiction. The lugs would as a bare minimum have to be mounted on insulated standoffs. I would never let a live lug be attached to wood directly. Wood is not an insulator, at best a semi conductor. I once touched a HV transformer from an electrostatic air cleaner with a neon volt checker taped on to a long broom handle and I found out the hard way what a lousy insulator wood and the case for that neon are.