to torque or not to torque

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The torque specs are part of the listing and labeling process. What method does the listing agency use to torque the connections?
 
I see this hasn't gotten into the copper vs. aluminum debate. I think we are all less concerned about copper. AL seems to be the tricky one. I know I have posted this before, and the standard answer seems to be using the torque wrench. (Even though all the 5+ EC's I've worked for, none of them had owned or used one on any of the jobs I was on). Still I agree with the earlier posts, best to find out from the listing agency as to what method they use. I use a lot of Milbank meters, wondering what they would recommend (other then a torque wrench). I know temp has a lot to do with how tight the connections are. After tightening lugs down when it's 60 + degrees, during the day, and come back the next day (after a 40 degree night) to find the terminations loose... (At least with AL.)
 
Power Tech said:
When installing split-bolts, I was taught. Tighten hit a few times and shake the connection then retighten.
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I was taught to tighten, bang on the head (the bolt's, not mine) with a hammer, tighten again, and repeat a couple of more times.
 
Kdog76 said:
I see this hasn't gotten into the copper vs. aluminum debate. I think we are all less concerned about copper. AL seems to be the tricky one. I know I have posted this before, and the standard answer seems to be using the torque wrench. (Even though all the 5+ EC's I've worked for, none of them had owned or used one on any of the jobs I was on). Still I agree with the earlier posts, best to find out from the listing agency as to what method they use. I use a lot of Milbank meters, wondering what they would recommend (other then a torque wrench). I know temp has a lot to do with how tight the connections are. After tightening lugs down when it's 60 + degrees, during the day, and come back the next day (after a 40 degree night) to find the terminations loose... (At least with AL.)
Click to expand...

My experience with Millbank is a lot of money for little product. Paid over $800 for a meter main that looks like something from HD for $80.
 
Shaking and banging

Shaking and banging

These both make sense to me. Most of our lugs and screws (meters, panels etc.) don't match the round shape or size of stranded wire so when you tighten down, you're going to change it's shape and the lay of the strands. "Shock treatment" will at least move the strands still in the insulation a little allowing the ones in the lug to settle better during re-torquing. Someone needs to design a better lug...
 
Torque specs generally are about 40 to 50% of stripping torque. So if you apply 3 times the proper torque you will strip the threads.
 
LarryFine said:
I was taught to tighten, bang on the head (the bolt's, not mine) with a hammer, tighten again, and repeat a couple of more times.
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Evidently, we went to the same school. I have repaired connections where this was not done and it just makes an expensive heater.
 
jxofaltrds said:
How do you check torque?

I thought 'once' torqued it could not be touched.
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That's for a normal bolt, or a nut and bolt. (When there's a nut, you're supposed to turn the nut, not the bolt, from what I've read in an automotive engiuneering book.) Re-torquing can over-stretch the bolt, causing a failure.

When you bang on a split bolt, you rearrange the conductor strands, so they fill any voids, and that loosens the tension, which is why you have to tighten it some more, and you should tighten last, not hammer last.

Bolts are actually tightened to the point of slight stretching, and it's that tension which holds the parts together. Engine cylinder head bolts are an example of this. They have to be stretched a bit for varying temperatures.

You know those huge mending plates that beams on overpasses are joined with? It's not the bolts' shear strength that holds the beam flanges together, it's the friction between the mending plates and the flanges.
 
jxofaltrds said:
How do you check torque?

I thought 'once' torqued it could not be touched.
Click to expand...

Not true at all for bolted connections ANSI maintenence standards require checking torque with a calibrated torque wrench, the main reason for this is loosening of the bolts from cold flow.

For wires in small panels however, you can damage the strands as don mentioned.
 
LarryFine said:
Agreed. In fact, when I re-terminate a smaller conductor, I cut and re-strip it, rather than squishing it even flatter.
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I have caught so much fire over the years from old bosses because of doing just that. It is just a habit I have grown into - start the termination with a fresh end of wire. But whenever I am in a panel, I always torque my lugs.
 
LarryFine said:
That's for a normal bolt, or a nut and bolt. (When there's a nut, you're supposed to turn the nut, not the bolt, from what I've read in an automotive engiuneering book.) Re-torquing can over-stretch the bolt, causing a failure.

You know those huge mending plates that beams on overpasses are joined with? It's not the bolts' shear strength that holds the beam flanges together, it's the friction between the mending plates and the flanges.
Click to expand...

I'm feeling safer already!!:grin:

FWIW, I just spent a week in August re-torqueing the bussbar nuts in the MCCs at a large manufacturing facility. These get re-torqued on a three year rotation.
 
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Mr. Wizard said:
I have caught so much fire over the years from old bosses because of doing just that. It is just a habit I have grown into - start the termination with a fresh end of wire. But whenever I am in a panel, I always torque my lugs.
Click to expand...

It makes perfectly good sense and I do that too. Anybody giving you fire ever give you reasoning for it?
 
I have found that using the small 18volt Dewalt impact wrench to make up gear is a great time saver and makes the job very easy. I have also found that no matter how hard you think the impact is torquing the screw, you can still get quite a bit of final movement with a torque wrench even when its set down to 28 or 32 ft lbs.
When I am done, the screw gets a witness mark and if space permits, I write the torque value on the lug.
 
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