Transformer Install

jayrad1122 · Jul 16, 2008

tonyou812 said:
jay are you a leffty?

why yes I am :-?

edit: was it the drill that made you wonder?

jayrad1122 · Jul 16, 2008

bakerbrotherselectric said:
If someone knows the code section for requiring a bond bushing at what voltage, it would help.. I thought it was 250v and over , and going through a concentric knockout.

nec 2008 250.97

bakerbrotherselectric · Jul 16, 2008

I read that section, which made me wonder why the bond bushing was on the 120/208v sec. According to that section and my understanding of it, the bond bushing should be on the 277/480v primary. ????
This would not be the first time my understanding of the code would be wrong, please correct me.

infinity · Jul 16, 2008

bakerbrotherselectric said:
I read that section, which made me wonder why the bond bushing was on the 120/208v sec. According to that section and my understanding of it, the bond bushing should be on the 277/480v primary. ????
This would not be the first time my understanding of the code would be wrong, please correct me.

In this case the bonding bushing is not required on either the primary or the secondary. If the primary (480 volt) had a concentric or eccentric KO knot not listed for bonding over 250 volts then a bonding bushing would be required. Below 250 volts they wouldn't be required even if a concentric or eccentric KO were used.

jayrad1122 · Jul 16, 2008

bakerbrotherselectric said:
I read that section, which made me wonder why the bond bushing was on the 120/208v sec. According to that section and my understanding of it, the bond bushing should be on the 277/480v primary. ????
This would not be the first time my understanding of the code would be wrong, please correct me.

250.97 says if concentric or eccentric ko's are used and not rated to be used as a reliable bonding connection you have to use them. But I punched my holes so I didn't need to use one. The one on the secondary side is as iwire and infinity says, a redundant ground. I just have it there because I treat it kinda like a service and bond my raceway.

Huevos · Jul 16, 2008

jayrad1122 said:
why yes I am :-?

edit: was it the drill that made you wonder?

Not sure what made him ask the question but, being right handed, I always hold the strap with my left hand and drive the screw with my right on a vertical run. Your screw hole on the one hole strap is on the left.

peter · Jul 16, 2008

Eggs,
Perhaps the stud behind the drywall is on the left hand side.

~Peter

quogueelectric · Jul 17, 2008

Huevos said:
Not sure what made him ask the question but, being right handed, I always hold the strap with my left hand and drive the screw with my right on a vertical run. Your screw hole on the one hole strap is on the left.

And the xformer cover is screwed on the left side of the xformer. We dont miss much do we???? clip on the screwgun is on the right side ect.....ect..... screams LEFTY!!!

Huevos · Jul 17, 2008

peter said:
Eggs,
Perhaps the stud behind the drywall is on the left hand side.
~Peter

Good point, never thought of that. Missed the clip on the drill motor too (even though the OP mentioned it). Guess I need to sharpen my observation skills....

Ragin Cajun · Jul 17, 2008

Nice. Be sure to keep the transformer off the wall 8-10" depending on manuf instructions. 50% of the cooling is out the back vents. Too often I've seen transformers slam up against the wall.

RC

mivey · Jul 17, 2008

It is hard to tell, but did you use Belleville washers, and in the 3rd picture (lug on right), is a Belleville washer installed next to the busbar, or is it an optical conclusion?

LarryFine · Jul 17, 2008

Nice work! Be proud.

jayrad1122 said:
I don't know how other transformer are but I didn't like how the lugs only faced the side, it would have been easier if they were facing forward.

You can always unbolt the lugs from the transformer, hold them with channel-type pliers while you tighten them, and then re-install them. It's better to not put that strain on the winding conductors anyway.

I noticed how close each phase's primary and secondary lugs are right away. I would have put them on facing away from each other, which is easy if you remove them to make them up anyway.

jayrad1122 · Jul 17, 2008

Thanks everyone!

Thanks everyone!

LarryFine said:
Nice work! Be proud.

You can always unbolt the lugs from the transformer, hold them with channel-type pliers while you tighten them, and then re-install them. It's better to not put that strain on the winding conductors anyway.

I noticed how close each phase's primary and secondary lugs are right away. I would have put them on facing away from each other, which is easy if you remove them to make them up anyway.

thanks for the tip that would have been easier

mivey said:
It is hard to tell, but did you use Belleville washers, and in the 3rd picture (lug on right), is a Belleville washer installed next to the busbar, or is it an optical conclusion?

I have no clue what a Belleville washer is. Care to explain:-?

jayrad1122 · Jul 17, 2008

Ohh and my No-Dog was waiting for me on the side of the panel this morning

quogueelectric · Jul 18, 2008

jayrad1122 said:
Ohh and my No-Dog was waiting for me on the side of the panel this morning

My life is complete!!!:smile::wink:

roger · Jul 18, 2008

Ragin Cajun said:
Nice. Be sure to keep the transformer off the wall 8-10" depending on manuf instructions. 50% of the cooling is out the back vents. Too often I've seen transformers slam up against the wall.

RC

Some new transformers are only requiring 3", I know this to be the case with SQ D.

Roger

jayrad1122 · Jul 18, 2008

roger said:
Some new transformers are only requiring 3", I know this to be the case with SQ D.

Roger

This one was set off I think 7", and manufactures instructions required 5"
I believe:-?

Ragin Cajun · Jul 18, 2008

roger said:
Some new transformers are only requiring 3", I know this to be the case with SQ D.

Roger

Sure enough. Although their wall brackets show 6". Learn something new every day.

TGIF!

RC

mivey · Jul 18, 2008

jayrad1122 said:
I have no clue what a Belleville washer is. Care to explain:-?

It would appear you have an aluminum to aluminum connection made with steel bolts. The disc-spring washer (Belleville washer) helps to maintain a constant pressure on the joint. The aluminum and steel expand at different rates and when the joint heats up, the aluminum becomes stressed and is deformed (undergoes plastic deformation).

The Belleville washer is usually made of spring or stainless steel that can absorb the expansion without being permanently deformed. There are other materials that can be used that also have good spring qualities.

Plastic deformation in the busbar causes a weakening of the joint because the aluminum does not recover from the stress and leaves gaps in the joint which oxidize.

The addition of a disc-spring washer helps absorb some of the difference in expansion between the steel and aluminum and have been shown to reduce the differential busbar stress by a factor of 10 (like 20 to 1, for example).

The flat washer should be at least twice as thick as the thickness (not height) of the Belleville washer, but no less than 1/8 to 5/32 inch thick.

see page 27 of:
http://portal.fciconnect.com/Comergent//fci/documentation/burndy%20connector%20theory%20-%202007.pdf

also read:
http://ecmweb.com/mag/electric_belleville_washers_correctly/

Now for the fun stuff:

The stress increase in the joint is proportional to temperature rise. The proportional function that relates stress and temperature rise gets some additional divisors when we add the disc-spring washer. We start with a proportional equation of (Ga-Gb)*Ab*Eb / (1 + t/a * (1+Ab/Aw) + (Ab*Eb)/(Aa*Ea)) without the Belleville washers.

The additional divisors we add (which reduce the proportional total) are: h/a + (Ab*Eb)/(a*K)

Ga is the busbar coefficient of thermal expansion, Gb is the bolt coefficient of thermal expansion, Ab is the bolt cross-section, Eb is the bolt's elastic modulus, t is the flat washer thickness, a is the busbar thickness, Aw is the apparent area under the flat washer, Aa is the apparent contact area of the joint, h is the disc-spring height, and K is the spring constant.

jayrad1122 · Jul 18, 2008

mivey said:
It would appear you have an aluminum to aluminum connection made with steel bolts. The disc-spring washer (Belleville washer) helps to maintain a constant pressure on the joint. The aluminum and steel expand at different rates and when the joint heats up, the aluminum becomes stressed and is deformed (undergoes plastic deformation).

Yes, this is an aluminum to aluminum connection with steel bolts. No I did not use Belleville washers, just flat washers with a lock nut. Will this be a problem down the road? :-? Its a 75kva xfrmr and feeds a 200a 208v wye. The panel will only have maybe 50A draw just from a bunch t8 6 lamp fluorescents and around 5 computers and some conveince outlets.

Thanks for the information, I will be sure to use them in more applications. :smile:

Transformer Install

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