Electrician Talk banner

What's your opinion on re-torquing mechanical lugs?

4350 Views 8 Replies 8 Participants Last post by  buddhakii
I will start by saying we avoid set-screw style lugs in favour of bolted compression lugs whenever possible, and that I think set-screw lugs especially for larger cables (say 1/0 or bigger) pretty much suck.

That said I run into them still.

What I run into commonly is lugs that were torqued to spec originally, but are way loose by the time the panel gets to the field.

For example today I checked a 1600A 480v transfer switch. Aluminum set screw lugs, parallel runs of copper 500kcmil.

The witness marks in the lugs were lined up, they hadn't backed off. But they were LOOSE. With a good shake I bet I could have pulled one out. I put the torque wrench on and the weight of the torque wrench could almost tighten the lug with no effort.

I re-torqued em. I got about 3/4 of a turn on each lug before it reach torque.

This is a 3/4" set screw. 3/4 of a turn is a LOT. Initially I adjusted the wrench all the way down just to see if I could tell how much torque was on them and it didn't even register at 120in-lb (spec is 650).

I understand there's always creep, and that after creep the contact resistance doesn't follow the same curve vs. pressure, but man when there's just no way they should be that loose.


I need to witness the panel shops torque procedures as well, maybe there's something up. I also realize they should get thermal scans but again when it's that crazy loose...
1 - 1 of 9 Posts
KennyW said:
That sounds like the right way to do it. I've heard its good practice to wiggle/shake the cable a bit while tightening. What I think happens on large cables especially is the strands don't really "settle" into the lug properly.
it also helps drastically to make sure the cable is shaped and wants to be sitting in that lug , with out constant force opposing the termination . I'm always fascinated by how loose feeling properly torqued connections are , but what do I know , lol ? I still prefer a slightly over torqued connection over a loose one any day .
  • Like
Reactions: 2
1 - 1 of 9 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.