[KennyW]

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.

Thoughts?

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...

 

[RIVETER]

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.

Thoughts?

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...

That is just a physical property of wire under compression. It will be tight and stay fairly tight until a bunch of movement and stacking, etc, occurs. The only really way to re-check is to do as you mentioned..."thermal check".

 

[Meadow]

Always tighten with a torque wrench. Feel of it is more of a guess, since its relative.

Thermal check, however only tighten if under torqued. If over torqued that can also cause overheating... it is possible to strip the threads or crush the strands.

 

[drsparky]

Proper torquing once should be good.

 

[Big John]

Proper torque on large conductors is often surprisingly loose. If you take a properly torqued mechanical connector, you definitely can work the wire back and forth to the point where the connector needs to be re-tightened, especially with soft aluminum.

I've never seen them so loose that they were at risk of coming out, so that's just a judgement call on your part.

I'm very much of them mind that it should be torqued once and left alone. I would've preferred a ductor or an IR scan before re-torquing. And if I suspected that aluminum connectors had been improperly installed, I would've cut off the abused ends and re-terminated.

 

[8V71]

Proper torque on large conductors is often surprisingly loose. If you take a properly torqued mechanical connector, you definitely can work the wire back and forth to the point where the connector needs to be re-tightened, especially with soft aluminum.

I don't work with large conductors often, and I don't know if this is good or bad, but I wiggle them back and forth while tightening. I can actually feel the lug getting loose while applying constant torque. When it stops turning and feels solid I finish up with the torque wrench.

 

[KennyW]

I don't work with large conductors often, and I don't know if this is good or bad, but I wiggle them back and forth while tightening. I can actually feel the lug getting loose while applying constant torque. When it stops turning and feels solid I finish up with the torque wrench.

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.

 

[drumnut08]

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 .

 

[buddhakii]

I don't work with large conductors often, and I don't know if this is good or bad, but I wiggle them back and forth while tightening. I can actually feel the lug getting loose while applying constant torque. When it stops turning and feels solid I finish up with the torque wrench.

You definitely want to do this but when terminating 500's or bigger in tight areas there's not much wiggle without risking breaking something so I over tourque just a hair.