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#124992 - 01/23/07 09:43 PM Transformer Conduit  
Admin  Offline

Joined: Oct 2000
Posts: 3,460
This is a 4 in PVC conduit that originates in a 1600A 480/277V 3 phase fused switchgear and feeds a single phase transformer. The transformer feeds a 240/120V 3 phase 800A breaker panel. The 4" PVC contains (3)350MCM conductors. The primary is fused @400A. This was installed in Nov. of '06. Check out the reducer to 3" where it turns into alum flex.

Fred White
Amptech Electric
[Linked Image]

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#124993 - 01/24/07 04:59 AM Re: Transformer Conduit  
iwire  Offline
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
I don't have a problem with the reducer.

I do see issues of lack of support.

A building inspector might also have a problem with taking out that large chunk of perlin.

Bob Badger
Construction & Maintenance Electrician

#124994 - 01/24/07 08:09 AM Re: Transformer Conduit  
HotLine1  Offline

Joined: Apr 2002
Posts: 6,883
Brick, NJ USA
Ditto on Iwire's comments.
Also, looks like a dusty/dirty enviro, basrd on the top of the xfr case.
A red


#124995 - 01/24/07 08:24 AM Re: Transformer Conduit  
Joined: Mar 2004
Posts: 251
Kingwood, TX USA
Maybe I missed something. Single Phase transformer feeding a 800 A 3 phase panel? If it is a 3 phase panel and only has 3 conductors where is the EGC. (remember, PVC feed) Robert.

#124996 - 01/24/07 10:15 AM Re: Transformer Conduit  
renosteinke  Offline
Cat Servant
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
This install fits in the "close, but no cigar" category.

Using the flex, I see no need for the 45 before the 90. Hence, no need to take that chunk out of the structural steel.

(There's a time, place, and method to cutting structural steel ... but this is not it!)

I'd like to see some support for that flex as well.

A few other notes:

Even were the conduit steel, a ground wire is necessary. A neutral is not (on the feed side).

For the life of me, I cannot imagine a situation where you would NOT want a neutral to the secondary panel.

I do hope there's a main breaker in that panel.

I do hope the transformer is grounded, including on the secondary side. Grounded both with a wire back to the GEC, as well as to that structural steel.

Likewise, the neutral buss ought NOT be bonded to the case ... your 'bond' is at the transformer.

Now ... into "forbidden territory." While the NEC has information as to sizing conductors and breakers, I've never seen an inspector check them. This job has enough signs of a well-intentioned, but unqualified, job that those decisions ought to be reviewed.

I also agree; a three phase panel fed by a single phase transformer is a worry. I consider it a technical violation of code (look at the panel listing).

#124997 - 01/24/07 02:47 PM Re: Transformer Conduit  
Fred  Offline
Joined: Apr 2001
Posts: 449
Straughn, IN 47387
No, there is not a main breaker in the panel. What you see just to the right of the transformer is a 400A fused disconnect which is just ahead of the 800A MLO circuit breaker panel. It contains (4) 200A breakers that feed other panels throughout the building as well as 20A 2 pole breakers that feed MH lighting. This electrical work was done by an EC hired by the building owner. I was hired by the tenant to install conduit/conductors and connect their equipment. I will get more pics tomorrow to give everyone a better overview of this situation.

#124998 - 01/24/07 07:50 PM Re: Transformer Conduit  
renosteinke  Offline
Cat Servant
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Thanks for the correction, Fred.

EC or not, I still think he could have done better.

#124999 - 01/26/07 08:46 AM Re: Transformer Conduit  
Trainwire  Offline
Joined: Mar 2002
Posts: 360
Pardon my ignorance.

I don't often work with this type of installation, and when I do it's under someone else.

That piece of pipe from the reducer to the transformer case looks all the world like a piece of flex exhuast pipe stuffed into a BX connector.

In all of my wanderings around the local warehouses I personally have never seen that style of conduit. I'm not saying there isn't,just I've never seen it.

It looks like someone cut the outer jacket off of a piece of metalic flex.

You have to give the installer a few points for creativity though.


Never underestimate the perversity of an inanimate object.

#125000 - 01/27/07 11:07 AM Re: Transformer Conduit  
BigJohn  Offline
Joined: Mar 2004
Posts: 391
Boston, MA

That stuff is legitimate. It's called flexible metallic conduit in the Code or Greenfield or "flex" in the real-world. It's very often used in short lenghts to make connections to equipment that vibrates, such as motors or transformers.

It's funny this should come up, because I was wondering about this practice the other day: Does anyone have any negative experience with non-flexible conduit being connected to transformers? The vibration is so slight that I have to question if FMC is even necessary. Especially since in many cases the pieces are of such a large diameter, and so short, that they aren't technically very flexible at all, and do very little to dampen the vibration of the tranny.


#125001 - 01/27/07 01:22 PM Re: Transformer Conduit  
renosteinke  Offline
Cat Servant
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Using flex for that final bit is a trade practice. One of those habits we get into....

The last few transformers I have installed have had the cores suspended inside, not rigidly attached to the case. With that sort of construction, it is likely that things will be just fine without that bit of flex. At least from a vibration point of view.

I still like having some flex in there. If nothing else, it allows for the unforeseen complications ... like the transformer being replaced, or shifting when a forklift bumps it, etc.

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