3/8" bolts in a 9/16" compression lug?

[Dale001289]

I noticed we have many 500kCMIL cables terminated with 9/16", 2-hole compression lugs but the attaching hardware is only 3/8". Also, they did not use lock washers under the hex head nut but rather flat washers in lieu of. If they meet the vendor torqueing requirements of 42 foot pounds, is this an acceptable connection?

 

[electrofelon]

I personally don't see an issue.

BTW IMO, and based on testing evidence of people who have actually tested them with a junker machine, lock washers serve no purpose, and often actually make the nut loosen quicker.

 

[don_resqcapt19]

It is probably fine, but I would not permit my guys to do that. I require that they install bolts that match the hole in the lug. I also require grade 5 bolt as most of the non-graded bolts available are cheap junk. The lock washer is not a big deal. If I used anything other than a flat washer, it would be a belleville washer.

 

[SceneryDriver]

I personally don't see an issue.

BTW IMO, and based on testing evidence of people who have actually tested them with a junker machine, lock washers serve no purpose, and often actually make the nut loosen quicker.

I came across a NASA paper on fastener and nut vibration proofing that actually said exactly that - split lock washers are less than useless. They either do nothing, or hasten loosening.

They do seem to help some when fastening soft materials, like plastic wire duct, to subpanels in control panels. They also seem to satisfy the bonding folks when used as a way to cut the paint on a device to be mounted, so there's that. But for metal to metal joints, they do nothing useful.


SceneryDriver

 

[don_resqcapt19]

I came across a NASA paper on fastener and nut vibration proofing that actually said exactly that - split lock washers are less than useless. They either do nothing, or hasten loosening.

They do seem to help some when fastening soft materials, like plastic wire duct, to subpanels in control panels. They also seem to satisfy the bonding folks when used as a way to cut the paint on a device to be mounted, so there's that. But for metal to metal joints, they do nothing useful.


SceneryDriver

Have only seen that theory applied to the "star" type of lock washer.

 

[electrofelon]

It is probably fine, but I would not permit my guys to do that. I require that they install bolts that match the hole in the lug. I also require grade 5 bolt as most of the non-graded bolts available are cheap junk. The lock washer is not a big deal. If I used anything other than a flat washer, it would be a belleville washer.

Yeah i see no reason to not just use the correct fastener to match. ALthough the exception is where you have factory studs or holes. I frequently use 1/2" hole lugs on 3/8 studs as that is the way the class 320 sockets we use come, and the lugs i like to use are hard to find in 3/8 hole.

Def agree on the ungraded/grade 2 crap. I will usually use grade 8, although I Admit that is not necessary.

 

[SceneryDriver]

Have only seen that theory applied to the "star" type of lock washer.

Split lock washers seemed to make my UL inspector happy. I thought they had to be star washers too - he said otherwise. I don't think he was right, for what it's worth.


SceneryDriver

 

[petersonra]

It is probably fine, but I would not permit my guys to do that. I require that they install bolts that match the hole in the lug. I also require grade 5 bolt as most of the non-graded bolts available are cheap junk. The lock washer is not a big deal. If I used anything other than a flat washer, it would be a belleville washer.

I have had this conversation with several lug manufacturers. The holes are not required by UL to be the same size as the fastening hardware.

I like Belleville washers too, but a lock washer if some sort is a good idea, but iirc, is not required by code or by UL listing.

 

[infinity]

I have had this conversation with several lug manufacturers. The holes are not required by UL to be the same size as the fastening hardware.

I agree and to the question in the OP using two 9/16" bolts on a 500 kcmil terminal is ridiculous. Often times 500 kcmil terminals come with a single 3/8" hole which is adequate if properly torqued. To think that two 9/16 bolts are really needed is a waste of time and money.

 

[don_resqcapt19]

I agree and to the question in the OP using two 9/16" bolts on a 500 kcmil terminal is ridiculous. Often times 500 kcmil terminals come with a single 3/8" hole which is adequate if properly torqued. To think that two 9/16 bolts are really needed is a waste of time and money.

I think two hole lugs are really to keep the lug from turning under high fault conditions. A single bolt can let the lug twist from the high magnetic forces.
That being said, I will always match the bolts to the size of the hole in the lug, if that is possible. If not, I will use something other than a standard flat washer to get the pressure distributed to the lug so that the contact pressure is correct. A large hole with a small bolt and a standard flat washer lets the washer bend and not apply the correct force to the lug.

 

[petersonra]

I think two hole lugs are really to keep the lug from turning under high fault conditions. A single bolt can let the lug twist from the high magnetic forces.
That being said, I will always match the bolts to the size of the hole in the lug, if that is possible. If not, I will use something other than a standard flat washer to get the pressure distributed to the lug so that the contact pressure is correct. A large hole with a small bolt and a standard flat washer lets the washer bend and not apply the correct force to the lug.

If it is torqued with a torque wrench to the appropriate degree, the force will be correct, regardless.

 

[retirede]

If it is torqued with a torque wrench to the appropriate degree, the force will be correct, regardless.

I think what Don is saying is that if the washer deflects into the hole, the force vector is no longer at 90 degrees so the clamping force will be lower.