Xfromer Torque Specs.

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big john

Senior Member
Location
Portland, ME
Been doing a lot of temporary transformers lately; they're all used; in the neighborhood of 112kVA. Where in the world do I find the torque requirements for the transformer lugs??

This is the first time I've done any transformers and I can't find the torque values on any of the labels or stamped into the lugs or anything. I'm not real comfortable just doing it by hand until it the metal squeaks, especially with aluminum....

-John
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
Or from the NECHB.

Commentary Table 110.3 Torques for Recessed Allen Head Screws

Socket Size Across Flats (in.) Torque (lb-in.)
1/8....................................................... 45
5/32.................................................... 100
3/16.................................................... 120
7/32.................................................... 150
1/4...................................................... 200
5/16.................................................... 275
3/8...................................................... 375
1/2...................................................... 500
9/16..................................................... 600

EDIT: Poor computer skills
 

big john

Senior Member
Location
Portland, ME
Thanks for the replies. Going online and getting the paper work seems like the best option when available.

How universal are those torque values from the handbook?

For the transformers I've done so far, I ended up getting the values off of similarly sized lugs and using those. The 5/16 hex were in fact 275 in./lbs. But I noticed that on breakers, the same size lugs might be 350 in./lbs. or more, so I wasn't too sure which number to pick....

-John
 

Rockyd

Senior Member
Location
Nevada
Occupation
Retired after 40 years as an electrician.
What the NECH commentary says -

Section 110.3(B) applies where terminations and equipment with tightening torques.

For the testing of wire connectors, for which the manufacturer has not assigned another value appropriate for the design. commentary Tables 1.2 through 1.5 provide data on the tightening torques that Underwriters Labratories uses. these tables should for guidance only if no tightening information on a specific wire connector is available. They should not be used to replace the manufacturer's instructions, which should always be followed.

That is the verbage from the 05 edition.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
How universal are those torque values from the handbook?
Electrical torque values are based on the size and material of the screw/bolt and the material being connector, therefore they are "universal".
However the torque value for the lug-to-transformer connection is taken from a "bus bar" table which may be a different value than the lug-to-conductor one.
 

big john

Senior Member
Location
Portland, ME
I think I'll be printing out a copy of that torque list to tape into my Ugly's book. It seems to match what I've been seeing in the field.

Thanks for the help, and happy Turkey Day!

-John
 

acrwc10

Master Code Professional
Location
CA
Occupation
Building inspector
Or from the NECHB.

Commentary Table 110.3 Torques for Recessed Allen Head Screws



EDIT: Poor computer skills

I had missed that table in the Hand book, Thanks Chris I went back and looked at it. I will definitely be going back to that table for reference. I like that it even has "split bolt" torque specs.
 
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