cable lug torques

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mull982

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Hello

I was wondering if anybody could explain to me the reason or importance of Torque Specs when tightening cable lugs? For example I am looking through an MCC spec sheet and it gives different torque specs for tighteing the cable lugs onto the busbars. I was wondering what the signifigance of these torque specs were, and how they effect the flow of current?

Thanks for the help

Mull982
 
They (torque values)don't affect the current flow ....directly...they affect HEAT .

A loose connection will arc and spark...creating heat...and the connection may fail as it deterioates.

An overtightened connection - with stressed threads - may fail under a heavy load condition(heat).
 
I would agree with Celtic,
Torque on C/B, Fuseblocks & Terminal strips has been required by UL to the manufacturers for the last 5-10 years. They say that if you properly torque to their published spec, you should not have a problem with amperage or heat.
Many studies have been done that say, under torquing is as bad as over torquing. Does this mean that you need to start walking around with a torque wrench? To the best of my knowledge nowhere in the NEC except article 409 (UL508A) does it require installers to recognize those established torque ratings.
Just my $.02
 
davidr43229 said:
Does this mean that you need to start walking around with a torque wrench? To the best of my knowledge nowhere in the NEC except article 409 (UL508A) does it require installers to recognize those established torque ratings.
Just my $.02
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110.3(B) would be the one that suggests you torque..IMHO.
 
Celtic,
I read 110.3B under Installation & use.
Listed or labeled equipment "shall be" installed and used in accordance with any instructions included in the listing or labeling.
Perhaps Contractors should start placing a torque wrench on their truck. I learned something, thank you
Dave
 
davidr43229 said:
Perhaps Contractors should start placing a torque wrench on their truck. I learned something, thank you
Click to expand...

They have a tendency to get "misplaced" by weekend warrior/auto-mechanic types :D
 
davidr43229 said:
I would agree with Celtic,
Torque on C/B, Fuseblocks & Terminal strips has been required by UL to the manufacturers for the last 5-10 years.
Click to expand...

Torquing has been part of instructions for more than 25yrs.
My first torque table from Square D was back in the early 80's.
 
Every peice of gear or equipment that you work on should have torqe specs
and yes you should carry a torque wrench

Lets strive to be as professional as we can be, and to follow the standards to the T - if and when a failure occurs - and the investigation ensues -
You don't want to get caught with your pants down
and you won't lose sleep because you know you you cut corners
 
For completeness sake, the Professional Electrical Apparatus Recycler's League ( PEARL ) has generic torque specifications in Table 1 of their "reconditioning standard". This is helpful when dealing with vintage and obsolete equipment, when it's being relocated, refed with new conductors, etc., when the original torque specifications are unknown and not available by other means.

http://www.pearl1.org/pdfs/pearl.pdf
 
I keep 2 on the truck. Ft/Lbs and In/Lbs. I'm always amazed at the look I get from some guys when I pull it/them out. That, and using a wire brush with Nolox(sp) nocorode for Al terminations.

Tom
 
celtic said:
Why Nolox (penetrox, etc) AL terminations?
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I don't usually use it for Cu. The Nolox instructions say to use a brush or emery cloth on the conductor. I don't have the exact instructions in front of me at this time though.

I reread the question, I agree it's not required, I feel that it can't hurt.:)


Tom:smile:
 
An overtightened connection - with stressed threads - may fail under a heavy load condition(heat).
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Rather than failing under a heavy load a stressed bolt may have the head snap off under the stresses that occur during a fault (OK a very heavy load), as for conductor termination connectors over tightening the Allen set can and does damage the conductor strands, particularly with aluminum.
 
Davis9 said:
I reread the question, I agree it's not required, I feel that it can't hurt.:)


Tom:smile:
Click to expand...

Not falling for the bait, eh? ;)

Good for you!

I agree with you, BTW :)
 
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