Another Transformer Question

[AmeL]

As always thanks for taking the time to read this and for your comments and recommendations.
We had a Contractor install brand new transformers in our plant, but something just doesn't look right. Please reference the attached images.
What is the required distance from the terminating lug to the transformer case?
Is there such a reference in the NEC regarding transformer installation?
Notice distance prior to wire terminations and after.
Has anybody experienced or serviced equipment that shorted bu pushing in or hitting the outside cover?

 

[winnie]

I'm confused. What else changed so that the terminal bus bars are now closer to the case?

The cable terminating lugs extend only a little bit past the bust bars, but the bus bars themselves look to be in different positions.

I am guessing here: you didn't make those measurements prior to the installation, but instead are having multiple transformers installed, and when you saw the problem in one transformer you went and made measurements of the 'pre-installation' clearance in another transformer. Am I anywhere close to the mark?

Is it possible that the transformer was rotated in its enclosure? Is it possible that one transformer was not manufactured correctly?

-Jon

 

[Pierre C Belarge]

I am curious, was the transformer engergized when you took the measurements?

Table 408.56 may give you some guidance, I do not know if the same at this table will hold true for transformers. I would look at a manufacturers site if you are very concerned.

 

[AmeL]

Thanks for reply Jon,
And you are right, I measured the distance on the one that hasn't been installed yet. The only thing that i see can happen that when you loosen the bolts that hold the rubber "feet' under it (as recommended) the whole transformer leans to the side due to the weight of the wire. Is that possible?

The transformers were not rotated, and we installed 3 of 150KVA ones and one 75KVA one and they look the same (too close to the cover). The distance is somewhat larger in 75KVA, about 2". Didn't measure the distance on this one prior to installation.

 

[BAHTAH]

Bus Bar Clearance

Bus Bar Clearance

IMO the clearance requirements for the transformer would be a NEMA standard. If you do not think the 1-1/2" - 2" shown is enough I would call the manufacture and see if what you have is ok. If your not going to sleep nights for the next forty years I would mount the lugs in the farthest hole from the cover and cut the bus bars. If you are worried about someone hitting the cover into the bars I would buy a sheet of insulating material and install it on the cover. I would not do any altherations unless the manufacture said it was ok and someone was willing to pay for it.

 

[Johnmcca]

Torque?

Torque?

I'm looking at the displaced strands under the bolts of the lugs in pics 1 and 2, and, have to ask, was that done with a torque wrench or did someone lean on the wrench and bend the bus bars out of position tightening them?

 

[benaround]

I've had a few that seemed too close to the cover, like Grant suggested, I put sheet

insulation on the cover to make me feel better.

 

[LarryFine]

What is the required distance from the terminating lug to the transformer case?
Is there such a reference in the NEC regarding transformer installation?

These seem to be manufacturer questions, not installation concerns.

 

[Power Tech]

Looks like factory installed connection points.

UL transformer, I see nothing wrong with it.

 

[bobsherwood]

Picture two... wow those lugs are close! Did you put your ruler there??? That bolt on the left is too long. I think I would have found a better arrangement for the lugs...

 

[nakulak]

312.11 A 3 gives a pretty good rule of thumb for minimum space required for <600 volts, although it doesn't exactly apply to transformer cases. I have also felt the need at times to put 3m insulators on the back of transformer case covers. If the transformers are in an area where the covers might get run into, then your concern is warrented. Otherwise, this is either a non issue or a manufacturer issue if you are not happy with the construction. (your cut sheets should be accurate with regards to clearances in the case).

 

[AmeL]

Pierre referenced the 408.56 table and according to this (live parts to ground if applies?? ) clearance needed for 208V would be 1/2" we have about 3/4" as seen on pic 2
The secondary voltage is 480V but those buss bars are the ones seen on pic 3 and are 1/2" further recessed.

The electrician also noticed that the primary connection was marked by X and secondary by H but the actual marking on the primary bars is H and secondary X.
The manufacturer REP agreed that it was wrong and will provide new stickers. Why would he ask us if we wanted the labels to have UL listed symbol on them?
Why would he provide labels without?

 

[AmeL]

Bob see picture 6, they are at two different levels.

 

[nakulak]

generally, you are not allowed to install those stickers.

 

[benaround]

Pierre referenced the 408.56 table and according to this (live parts to ground if applies?? ) clearance needed for 208V would be 1/2" we have about 3/4" as seen on pic 2
The secondary voltage is 480V but those buss bars are the ones seen on pic 3 and are 1/2" further recessed.

The electrician also noticed that the primary connection was marked by X and secondary by H but the actual marking on the primary bars is H and secondary X.
The manufacturer REP agreed that it was wrong and will provide new stickers. Why would he ask us if we wanted the labels to have UL listed symbol on them?
Why would he provide labels without?

amel, The primary of this transformer is 208volts (X) and the secondary is 480Y/277 (H)

you better double check whats going on!!!

 

[benaround]

amel, the copper bars with the adjustable taps on them are the primary.

 

[Besoeker]

This is what happened when clearances were not adequate....

http://www.youtube.com/watch?v=nibB2c9djCo