250.30 ~ I need a picture...

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celtic

Senior Member
Location
NJ
I need a picture or two showing the XO to ground connection on a transformer "in the real world".

Typical 480 -208/120 stepdown...nothing fancy.

Similar to these from Mike:

1014156418_2.gif


1015005801_2.gif


1100200751_2.jpg


1100880388_2.jpg


or this one from the NECH:
Exhibit2501325030.jpg



Anyone have a real world example of the "star" ~ building steel, EGCs, etc.


TIA
 
Two things of note that I see in the photos.


The manufacturer's silver colored strap on the right hand side of the picture is not the system bonding jumper. One still would need to be installed.

The lug used to bond the GEC to the grounded terminal is most likely field installed, if so, it is not a permitted method of adding terminals.


Otherwise, those are some good pictures of the transformer.
 
Why is that?
Should a double barrel lug be used?


Adding a lug on top of a lug already in place is not permitted. I took a class with UL and the instructor stated that the temperature of the lug surface and the bolt shank is not designed for this purpose.


It doesn't hurt...that's for sure....but what I am really looking for is a shot of the "star".

What do you mean you are looking for a shot of the "star?"
 

celtic

Senior Member
Location
NJ
Adding a lug on top of a lug already in place is not permitted. I took a class with UL and the instructor stated that the temperature of the lug surface and the bolt shank is not designed for this purpose.




What do you mean you are looking for a shot of the "star?"

So a stack of lugs attached to the frame of the transformer with 1/4 x 20 hardware is NFG?
The lugs would be containing:
- primary EGC
- secondary EGC
- bonding jumper
- building steel grounding conductor
- jumper from XO

This is the "star" I speak of.
 

Volta

Senior Member
Location
Columbus, Ohio
Adding a lug on top of a lug already in place is not permitted. I took a class with UL and the instructor stated that the temperature of the lug surface and the bolt shank is not designed for this purpose.

Can you tell us more about this? If it was a simple 1/4-20 bolt it may not have been designed to carry current, but would provide tension. Would the back of the lug not be acceptable to connect to the face of the lug under it?
This may be a bolt provided by the manufacturer for the purpose of holding a single lug, I know.

Can two (or more) lugs be bolted together in lieu of a splitbolt?
 
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The lugs and bolts that are supplied with equipment when sent from the factory, have been tested at the factory to perform in a way specified by the manufacturer.
Once one starts to change those configurations, it is no longer known if the said change will function as the specifications at the factory. Therefore, without some kind of testing in for the field modification, it is not a permitted installation.
That is what I learned recently at a UL class.

Note:
The specifications may or may not be a standard, they could be specifications set forth by the manufacturer.
 

joebell

Senior Member
Location
New Hampshire
The lugs and bolts that are supplied with equipment when sent from the factory, have been tested at the factory to perform in a way specified by the manufacturer.
Once one starts to change those configurations, it is no longer known if the said change will function as the specifications at the factory. Therefore, without some kind of testing in for the field modification, it is not a permitted installation.
That is what I learned recently at a UL class.

Note:
The specifications may or may not be a standard, they could be specifications set forth by the manufacturer.


So does this mean if a transformer is shipped without lugs attached (very common) this installation should be field tested? By who UL or some other NRTL?
 

tkb

Senior Member
Location
MA
Adding a lug on top of a lug already in place is not permitted. I took a class with UL and the instructor stated that the temperature of the lug surface and the bolt shank is not designed for this purpose.

Is there a document to confirm this?
Lugs don't usually come with these types of transformers.
 
The lugs and bolts that are supplied with equipment when sent from the factory, have been tested at the factory to perform in a way specified by the manufacturer.
Once one starts to change those configurations, it is no longer known if the said change will function as the specifications at the factory. Therefore, without some kind of testing in for the field modification, it is not a permitted installation.
That is what I learned recently at a UL class.

Note:
The specifications may or may not be a standard, they could be specifications set forth by the manufacturer.



Notice what I wrote in my previous post...

When not supplied, I would guess the manufacturer is leaving it up to the installer. What do the installation instructions say about terminations in those types of shipments of transformers?
 

celtic

Senior Member
Location
NJ
What do the installation instructions say about terminations in those types of shipments of transformers?

Not much:
6.1 Cable Conduit Entrance / Lugs
All general-purpose transformers are designed for easy accommodation of cables and cable connectors.
Lug connector kits are readily available and can be ordered through the sales office, through the distributor or can be purchased commercially. The assembly of connectors to the line terminals is important. Follow established installation procedures recommended by the connector manufacturer.
Do not install washers between the lug and the terminal. This will cause heating and arcing, resulting in failure of the connector. Refer to the NEC and cable connection guide on inside front cover of transformer for sizing. Follow torque recommendations of the connector manufacturer or use the
following guide.
Dry-Type General Purpose Power Transformers Single and Three Phase, 15-1000 KVA Installation Guide

[I had to save the PDF to get it to open...link probably messed up at GE...here is the page link is on : http://www.geindustrial.com/publibr...&pubType=Installation and Instruction&src=cwc ]


EDIT TO ADD:
6.2 Grounding
Consideration must be given to equipment grounding (case, core, and transformer winding). Grounding methods and practices are well established and are beyond the scope of this installation guide. ANSI/IEEE standard 142 is a recommended publication for this subject and contains an extensive bibliography. The grounding conductor for a transformer should have a current carrying capacity in accordance with the National Electrical Code.

 
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Karl H

Senior Member
Location
San Diego,CA
Most Transformers I install either do not come with lugs or if they do,

XO is usually a single lug. I remove the single lug and install a double lug

using the manufactures hardware to attach it. Then I install a system bonding

jumper sized per T-250.66 to bond all EGC and GEC to XO. I never "Double-

stack" lugs. I think that the reason that the Transformer Manufacture only

provide a single lug for XO,or any lugs for that matter is either to save

money or they would prefer you to install the system bonding jumper at the

first disconnecting means. I don't know why,but, I'd rather instal the system

bonding jumper to XO in the transformer. The ground strap you see in

transformers is to bond the frame since most transformers today have

rubber isolation grommets to reduce hum or noise. That's just my opinion

I'd like to know if that's true or not.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Here's a 500 KVA. 1st photo the bonding jumper is attached to the XO, second photo it's attached to the ground bus. Also in the photo is the #3/0 GEC.

20080209_58.JPG


20080209_59.JPG
 
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