RichB
Senior Member
- Location
- Tacoma, Wa
- Occupation
- Electrician/Electrical Inspector
Wow--Awesome discussion-- 
Proper torquing method
- Thread starter RichB
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Tulsa Electrician
Senior Member
- Location
- Tulsa
- Occupation
- Electrician
Well today it just so happened we're reinstalling two 400 amp 480 volt panle boards. These Pics are of the lugs on the main breaker. Signs of being over tightened. Threads pulled.
I was not able to check as some one else removed equipment. I instructed them to cut wires and do not take loose. Now no way to check. The guy removing was the one that installed first time. So tommorow a confession will take place. Some one is going to show me his gear bag.
I was not able to check as some one else removed equipment. I instructed them to cut wires and do not take loose. Now no way to check. The guy removing was the one that installed first time. So tommorow a confession will take place. Some one is going to show me his gear bag.
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Tulsa Electrician
Senior Member
- Location
- Tulsa
- Occupation
- Electrician
Now we have to decide to find replacement or use single larger conductors. We can no longer use parallel. Shop looking for a new lug kit.
FionaZuppa
Senior Member
- Location
- AZ
- Occupation
- Part Time Electrician (semi retired, old) - EE retired.
Final TQ should be done in one motion from no more than about 75% of final TQ #.
If you get too close and stop, the static friction that's there may be enough to make the break-free TQ higher than desired final #. Hence, it will click even before the screw starts to move.
If you want to set the wire and check it, go to 75% desired TQ, check it, then finish off to desired TQ in continuous motion.
What I never see in instructions for electrical screws/bolts (lugs, etc), they never say to lubricate the threading. A smidge of noalox on the beginning threads will not only keep it from seizing, it helps to obtain TQ accuracy.
Do any lugs that call for TQ # have a ± spec, like ±10 or ±5% ?
As for "TQ, loosen, then TQ again"? Yes, but this is not for the strands to "compress". This method is to combat threading issues. TQ then loosen 1x 2x 3x will help mate threadings, helping to bring even force across the threading once final TQ is there. With a bad thread mating you could essentially land all the force from TQ across 2-3 threads of the 12 thread screw, but over time the TQ may lower as those 2-3 threads relax and stretch.
If you get too close and stop, the static friction that's there may be enough to make the break-free TQ higher than desired final #. Hence, it will click even before the screw starts to move.
If you want to set the wire and check it, go to 75% desired TQ, check it, then finish off to desired TQ in continuous motion.
What I never see in instructions for electrical screws/bolts (lugs, etc), they never say to lubricate the threading. A smidge of noalox on the beginning threads will not only keep it from seizing, it helps to obtain TQ accuracy.
Do any lugs that call for TQ # have a ± spec, like ±10 or ±5% ?
As for "TQ, loosen, then TQ again"? Yes, but this is not for the strands to "compress". This method is to combat threading issues. TQ then loosen 1x 2x 3x will help mate threadings, helping to bring even force across the threading once final TQ is there. With a bad thread mating you could essentially land all the force from TQ across 2-3 threads of the 12 thread screw, but over time the TQ may lower as those 2-3 threads relax and stretch.
VirutalElectrician
Senior Member
- Location
- Mpls, MN
- Occupation
- Sparky - Trying to be retired
Seems like there's several different methods that people think are appropriate. Which begs the question, has anyone ever heard from Schneider or Siemens on what method they think is correct?
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Maybe this is a question for the SAE. 
letgomywago
Senior Member
- Location
- Washington state and Oregon coast
- Occupation
- residential electrician
What if they end up having different answers?
ptonsparky
Tom
- Occupation
- EC - retired
Then it is answered with complete agreement here.
(Clean, Dry threads only. No lubrication)
FionaZuppa
Senior Member
- Location
- AZ
- Occupation
- Part Time Electrician (semi retired, old) - EE retired.
My post #24 is based directly from the physics of it. The actual prescription of TQ by a lug maker is on them. If it does not matter what final is, then the most basic direction is "torque to 35ft-lb". Basically three words w/o regard to threading or accuracy. Just go look at the directions that call out a TQ #, notice how the details are missing, which indicates it's a crude method to lock it down.
The most specific prescriptions I can think of comes from aerospace (air and space) industry. Threading/Mating specs, lubrication/threadlock, procedure, type of TQ method (to yield vs final TQ wrench reading, etc).
The most specific prescriptions I can think of comes from aerospace (air and space) industry. Threading/Mating specs, lubrication/threadlock, procedure, type of TQ method (to yield vs final TQ wrench reading, etc).
VirutalElectrician
Senior Member
- Location
- Mpls, MN
- Occupation
- Sparky - Trying to be retired
GeorgeB
ElectroHydraulics engineer (retired)
- Location
- Greenville SC
- Occupation
- Retired
The RIGHT, and 99.9999% of the time impractical, is by measuring stretch.
The situations I've used this used one of three methods to measure it; lubricants don't interfere.
1. hollow bolts or more usually studs tightened to about 10% of calculated torque, then drop a "calrod" element in, wait an hour or 2 and turn the nut a certain angle
2. a machined center drill in the bolt/stud ends, a micrometer over balls in the centers
3. a bolt stretcher that creates the initial gap then turning an angle as in 1
The situations I've used this used one of three methods to measure it; lubricants don't interfere.
1. hollow bolts or more usually studs tightened to about 10% of calculated torque, then drop a "calrod" element in, wait an hour or 2 and turn the nut a certain angle
2. a machined center drill in the bolt/stud ends, a micrometer over balls in the centers
3. a bolt stretcher that creates the initial gap then turning an angle as in 1
Tulsa Electrician
Senior Member
- Location
- Tulsa
- Occupation
- Electrician
rambojoe
Senior Member
- Location
- phoenix az
- Occupation
- Wireman
Some of these guys should put some of these suggestions on a aircraft mechanics forum...Maybe this is a question for the SAE.
rambojoe
Senior Member
- Location
- phoenix az
- Occupation
- Wireman
Neat story. Many years ago during all of the wally Marty solar stuff.. a shut down and connect/restart with inspectors eng's., wally regionals and all associated bosses and such..
Kinda back in the beginning of those juicy jobs. Long story short-...
Its 12am, store is shut off, I get through modifying my main section of multi barrel lugs and handing my personal torque wrench to a newbie and knowing that my boss will need diff torque values I say "here, set it back to zero and give it to don". I love high pressure stuff like this BTW, so with my time and 1/2, I'm loving it.
Right as I'm wondering what's taking greenie so long he says -
"It won't go to zero!" As I turn to see him gorilla wrenching the handle on my $400 snap-on I realize... the wrench starts at 50ftlbs and he is trying to get it to an actual imaginary "0". He broke it and I had the only wrench that night. The 60lb values i just set were clicking at a "now incorrectly" indicated 150ftlbs or such. Boss ran diversion with inspectors because by then they were satisfied with our work. Kid got canned, boss replaced my wrench and I won't say what I did the next night. But it was scary, my new wrench was mastic taped and all my "guess" were on point. Engine building saved my companies butt that night, utility companies and inspectors signed off on it, power went on and the night stockers went back to work...
Have a back up.
Kinda back in the beginning of those juicy jobs. Long story short-...
Its 12am, store is shut off, I get through modifying my main section of multi barrel lugs and handing my personal torque wrench to a newbie and knowing that my boss will need diff torque values I say "here, set it back to zero and give it to don". I love high pressure stuff like this BTW, so with my time and 1/2, I'm loving it.
Right as I'm wondering what's taking greenie so long he says -
"It won't go to zero!" As I turn to see him gorilla wrenching the handle on my $400 snap-on I realize... the wrench starts at 50ftlbs and he is trying to get it to an actual imaginary "0". He broke it and I had the only wrench that night. The 60lb values i just set were clicking at a "now incorrectly" indicated 150ftlbs or such. Boss ran diversion with inspectors because by then they were satisfied with our work. Kid got canned, boss replaced my wrench and I won't say what I did the next night. But it was scary, my new wrench was mastic taped and all my "guess" were on point. Engine building saved my companies butt that night, utility companies and inspectors signed off on it, power went on and the night stockers went back to work...
Have a back up.
SparkyBirdman
Member
- Location
- Folsom, CA US of A
- Occupation
- Electrical Contractor
Laughed pretty hard at those 2! I too am glad for the question. Interesting takes
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