Anti-seize compound on outdoor breaker lugs

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jap said:
I've yet to torque a lug on a breaker, Panel or meterbase with a torque wrench to spec without feeling like It's fixing to break completely off even with the aid of a wrench to keep the lugs from twisting.

JAP>
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Thats odd, Usually I hear people say the torque spec feels way looser than they would have done it without a torque wrench.
 
electrofelon said:
Thats odd, Usually I hear people say the torque spec feels way looser than they would have done it without a torque wrench.
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Some devices have somewhat low torque requirement, some have fairly high requirement.

At same time the length of fulcrum of tool can fool you into thinking you applied more or less torque than with some other tool.

250 in-lb with a 12 inch long handle wrench seems like nothing compared to using one of those allen sets that is like a swiss army knife allen wrench set and you only have a 5 or 6 inch handle to use and get same torque out of it.

Then to tighten a smaller screw to only 20 in-lb with a simple torque screwdriver seems like a lot but look at how small the radius of the handle is compared to length of about any wrench type tool.
 
mikeames said:
Torque is torque but the pressure put on the lug and the conductor will be greater if there is less friction in the threads. This is also true when engine building. They will specify torque with and without additives.
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What about re-torquing at a later date for PM?
 
As Larry mentioned the lug will stretch and the conductor yield. Re-torque for PM. The re-torque will re-apply the required pressure on the conductor after material creep has set in.
 
mikeames said:
As Larry mentioned the lug will stretch and the conductor yield. Re-torque for PM. The re-torque will re-apply the required pressure on the conductor after material creep has set in.
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That is taken into account with the original torque spec, the creep or relaxation at the wire termination does not result in a higher connection resistance. Burndy says this about connections where the screw applies direct pressure on the wire.
The question arises as to whether it is necessary to retighten the bolts to the original torque value. In a properly designed connector,
retightening is unnecessary since the contact resistance should increase very little due to the relaxation of pressure,
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don_resqcapt19 said:
That is taken into account with the original torque spec, the creep or relaxation at the wire termination does not result in a higher connection resistance. Burndy says this about connections where the screw applies direct pressure on the wire.
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Makes sense, good to know.
 
GoldDigger said:
But the relationship between the elongation and the torque required is still strongly dependent on the thread friction.
Your point is well taken if instead of measuring torque you specify "finger tight plus N turns". That is independent of thread friction.

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If you have really gunked up threads, finger tight might be different than clean or lubricated threads.
 
Use your non dominant hand, it knows torque.
Would the heating/ cooling of a lubed thread untorque vs dry?
 
don_resqcapt19 said:
That is taken into account with the original torque spec, the creep or relaxation at the wire termination does not result in a higher connection resistance. Burndy says this about connections where the screw applies direct pressure on the wire.
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I believe that one of the goals of the initial compression is to force a gas-tight connection between the mating surfaces.
 
mikeames said:
As Larry mentioned the lug will stretch and the conductor yield. Re-torque for PM. The re-torque will re-apply the required pressure on the conductor after material creep has set in.
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That overstretches the lug. Properly torqued you are close to 85% of yield. So if you tighten more you are over tightening and permanently deforming it. That’s when strength goes down setting yourself up for failure.

That is not what happens. When you first torque first you crack and break the oxides at alpha spots. Further pressure expands the spots. It is direct metal on metal contact...cold welding. Subsequent relaxation almost all the way to failure barely changes the conductivity at all. You can read about this in the Burndy book or Cooper or several others or simply put a micro ohmeter on it and watch what happens as you loosen it,
 
paulengr said:
Properly torqued you are close to 85% of yield.
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Back in an earlier career dealing with fasteners, I believe it was the ASME that said applied stress could not exceed 1/3 of tensile strength or 2/3 of yield point.

I agree that 85% would be good, but how would it (or my 2/3<?>) be determined in the field anyway.
 
electrofelon said:
Thats odd, Usually I hear people say the torque spec feels way looser than they would have done it without a torque wrench.
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I agree with that when I'm torqueing bolts on an engine, but, on electrical connections the torque specs given seem way too tight with the same torque wrench being used.

At least that's been my experience with them.

JAP>
 
GeorgeB said:
Back in an earlier career dealing with fasteners, I believe it was the ASME that said applied stress could not exceed 1/3 of tensile strength or 2/3 of yield point.

I agree that 85% would be good, but how would it (or my 2/3) be determined in the field anyway.
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Not sure where those ASME rules came from because they don’t match current recommendations. The tensile strength I can understand but it’s still a swag.

You can guess at it knowing the nut factor. If you know the tension spec and there are charts based on material, diameter, and a nut factor, you can calculate foot pounds needed. If you want to go past the basics...


Machinery’s Handbook gives the basic numbers, as does the Fastenal handbooks.

The thing is what we want is tension on the fastener..how much it is squeezing everything together. You can measure this accurately by measuring bolt stretch ultrasonically. A torque wrench really measures torque on the nut. 80% of the torque is friction in the threads. Only about 10-15% is actually tension...what we want. So it’s not the best way to do it but it’s the best we got. Using a thread lube, ANY thread lube, using the proper fastener, using a torque wrench...all contribute to getting very close to proper tension. Brass and copper alloys are naturally self lubricatjng, stainless and aluminum are definitely the opposite issue due tendency to easily gall. This gets us down to around +/-25% or better. Based on just mushing alpha spots there is a large window of acceptable tension which is why we don’t need precision tension but electrician “feel” fails more often than you would think. The required tension is pretty universal because really we only have a few conductor materials we work with (copper, aluminum).
 
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