Torque Specs on lugs

[sokkerdude]

Is there a standard torque spec for lugs according to there size? Or are they according to manufacturers? I have a 3000 amp transfer switch with the lugs
so close together that i barely get a "L" 1/2 in Allen wrench in to tighten them. How does one torque them to specs if you can't get a torque wrench on them? If I remove a set of lugs to be able to use a torque wrench, do I blow the manufacture warranty on the transfer switch, if any thing was to go wrong. Thank you

 

[hillbilly]

I made my own drivers to torque terminals. I cut the "L" off of some long allen wrenches and got 1/4" drive, hex sockets to fit the different sized allens and taped them on.
I can use the drivers and any needed 1/4" extensions to reach just about anything inside a panel. Using a 1/4" drive makes it easier to get the tool into tight places. I adapt to my 3/8" torque wrench with a 1/4 x 3/8 socket reducer.
What is the listed torque on the screws? A 1/4" drive may not withstand the torque required for the 3000A lugs.
You can buy the allen wrenches with the driver attached, but the ones that I've seen have a 3/8" drive, plus I like to make my own tools if I can.
I use the torque spec. that's listed on the enclosure, and always torque to maximum allowed. I don't know of a standard torque for each size although there probably is one. I know that GE panels have a standard label that gives the torque according to the internal dimension of the allen across its flat sides.
hope this helps
steve

 

[RayS]

I don't know of a standard torque spec, but has anyone else noticed the need to retorque the bigger lugs after install? It seems like they creep loose, and need torqued a week later. After that they seem to stay tight- maybe most of the creep is gone by then. I've had starters come in with the wire falling out of the lugs, and I'm pretty sure the factory actually torqued it.

 

[cpal]

This may help usually the manufacture will provide tissue paper with the information you are looking for

Modified wrenches do not guarantee acurate torques.


http://www.ilsco.com/newweb/IlscoHome.nsf/Web+Pages/Torque+Information

 

[hillbilly]

Modified wrenches do not guarantee acurate torques.

Torque is torque. The skill of the installer and the accuracy of the torque wrench guarantees accurate torque (or not).
(IMO) Straight line torsion of the extension has no effect on the sum of the applied torque.
How's that for a thesis?
steve

 

[don_resqcapt19]

I assume that these lugs are side by side, with the set screw facing the ajacent lug preventing the use of any tool other than a "L" hex key wrench. In some cases, even the short end of the "L" is too long to fit in the space between the lugs. I have seen a number of panels built this way. Not sure how you torque these.
Don

 

[cpal]

Modified wrenches do not guarantee acurate torques.

Torque is torque. The skill of the installer and the accuracy of the torque wrench guarantees accurate torque (or not).
(IMO) Straight line torsion of the extension has no effect on the sum of the applied torque.
How's that for a thesis?
steve

I'm not sure of stright line I would expect the torque would be accurate, I've used offset wrenches that were modified as such and I watched the arms bend to some degree I would not have a lot of confidence in accurate torque in those conditions.

 

[NoVA Comms Power]

... Not sure how you torque these ...

With an offset adaptor.

Correction formula to be used for an extension is at:
http://www.engineersedge.com/manufacturing_spec/torque_wrench_1.htm

or for a reducer:
http://www.engineersedge.com/manufacturing_spec/torque_wrench_2.htm

The "Open Calculator" link on both pages provides a nifty tool once you understand the theory.

 

[templdl]

Torque values go back to the point where the lug is tested with the cable for temperature rise and a "pull test" per UL requirements. When a lug is torqued to that as specified by the mfg. that value goes back to that which it was tested and should guarantee that the lug/cable combo will operate within the temp. rise allowed as well as being able to pass a pull test.

 

[infinity]

I assume that these lugs are side by side, with the set screw facing the ajacent lug preventing the use of any tool other than a "L" hex key wrench. In some cases, even the short end of the "L" is too long to fit in the space between the lugs. I have seen a number of panels built this way. Not sure how you torque these.
Don

I have seen equipment constructed in that fashion with lugs facing each other. The reality is the L shaped hex key goes in the lug, an 18" pipe is sleeved over the key handle, and the thing is tightened as tight as it will go. It should be in the part of the manufacturers' design process to not design things that cannot be torqued.

 

[charlie tuna]

being in the infrared scanning service since 1989 we have found many of these somewhat un-accessible lugs with heat problems. but if a termination is properly made --- meaning "enough" torque --- but also meaning "not overtorqued" and that termination is not overloaded -- it should never fail.. proper torque is a figure recommended by the manufacturer of the terminal. but then consider a copper/aluminum lug. if the threads of the lug are dry or not lubricated it will reach the recommended torque setpoint sooner than one that is lubricated. the guy with the 18 inch pipe over the end of the allen wrench can perminently damage anything he comes across. terminating takes some common sense at times there are problems with accessibility. we have designed or cut off allen wrenches of various sizes and used socket type torque wrenches with a socket that fits the cut off allen wrench. also we carry the allen sockets. we have scanned buildings where many of the building's disconnect switches were perminently damaged by the installer due to over-torquing. once the line side blade is bent out of alienment it's surface area is reduced and can cause overheating depending on how bad the connection was over-torqued. we use kno-lox on all large wire terminations -- both copper and aluminum. and generally, when we scan a building that the contractor has gone through the trouble to use a terminal inhibiter on the terminations the terminations are good. on one particular large transfer switch it had a four wire -- "stacked" terminal block that showed up as a heat problem. being it fed emergency power in a hospital it was difficult to schedual a shutdown. we suspected the back two wire terminations were loose? we torqued them and gained some torque and thought we had solved the problem. the next year this same terminal showed again as a heat problem. we then found out the surface area between the lug and the copper bus was insufficent to carry the lug's rated amperage. we extended the copper bus high enough to maximize the lug's surface contact area and that solved the problem.

 

[NoVA Comms Power]

Charlie Tuna:

Very interesting post.

This thread seems to have gotten electronically "fouled-up" , out-of-sequence, and one particular post from yesterday about the use of ferrules is now MIA.

Do you have any observations or experiences re: the use of ferrules to improve the reliability of stranded connections to share?

 

[charlie tuna]

nova,
what are ferrules?? you mean high press terminations?? if so, yes they are less likely to fail. but again, like many things in our trade, they must be installed per the recommendations of the manufacturer. if the high press tool is not certified or tested regularly it could be releasing the the termination before it actually reached it recommended compression. and also if the high press tool is not sized for that termination it will not reach it's proper compression point.

we were hired to infrared an addition in an airport that had a problem with failing high press terminals. we found the cause to be the contractor did not own a high press tool and rented one from his supply house!!!! it was only applying about 60 per cent of the recommended pressure to the termination and releasing. sure the crimp looked squeezed and held the wire in it's sleeve, but under load they began to fail. the supply house ended up hiring another contractor to re-terminate all the airport addition's high press terminations. and we have come across problem high press terminations where someone used "aluminum only" terminations on copper!

again--common sense--prevails. we had four high press tools and they were rebuilt and re-certified as soon as they started leaking. we never loan them out and always select a knowledgable electrician to operate or oversee any high press terminations... and i think it is wrong for any supply house to rent out tools....................

 

[tallgirl]

I don't know of a standard torque spec, but has anyone else noticed the need to retorque the bigger lugs after install? It seems like they creep loose, and need torqued a week later. After that they seem to stay tight- maybe most of the creep is gone by then. I've had starters come in with the wire falling out of the lugs, and I'm pretty sure the factory actually torqued it.

Metal deforms over time (this isn't news to anyone, right?) It's not so much that whatever it is is creeping loose, like the screw, bolt or lug is turning backwards, but that the metal itself -- lug, wiring, etc. -- is deforming.

If you'd like to see for yourself how this works, get a paint stick (or bottle of nail polish -- I won't tell anyone), and paint a mark across the lug after you've torqued it. Come back a week later and retorque. You notice that the mark hasn't changed.

 

[don_resqcapt19]

tallgirl,

If you'd like to see for yourself how this works, get a paint stick (or bottle of nail polish -- I won't tell anyone), and paint a mark across the lug after you've torqued it. Come back a week later and retorque. You notice that the mark hasn't changed.

Wire connections of the set screw type should never be "retorqued". The original torque spec accounts for the "creepage". Retorquing can increase the creepage to the point that the connection fails. Look at this document.
Don
http://www.mikeholt.com/code_forum/editpost.php?do=editpost&p=615212

 

[charlie tuna]

don, your are correct --- the first organization to track this was general motors. they had a schedualled maintainance torque program. they found out they were creating more problems by re-torquing terminations. maintainance records proved this to be true!!! once a termiation is correctly made it should remain in good condition unless overloaded. take a mechanical bug. tighten it to it's rated torque -- let it stand for five minutes -- take a hammer and tap the lug lightly on the none threaded end. let it stand five minutes and re-torque it -- you should get some movement on the thread. do this till there is zero change in the thread and you have the best situation that termination can be in!!!

 

[templdl]

Don, While assigned as a sales and application engineer for a leading breaker mfg. that's exactly what our policy was, once torqued correctly do not retorque. Infrared scans should be done regularly as a matter of maintenance practice.
One thing that I did observe is that if a connection does start to heat, a heating and cooling cycle will cause the connection to further degrade by loosening the connection father which results in increased heating. If left unattended, in some cases the connection may start to arc, ionizing the air which then can involve a phase to ground and phase to phase arcing fault.
So it's important to observe good torquing and maintenance practices.
Dave T

 

[don_resqcapt19]

Dave,

So it's important to observe good torquing and maintenance practices.

And the correct maintenance practice when there is evidence of a problem is not to tighten the connection. You need to shorten the wire and re-terminate as well as replace the lug.[FONT=&quot]
Don
[/FONT]

 

[tallgirl]

tallgirl,

Wire connections of the set screw type should never be "retorqued". The original torque spec accounts for the "creepage". Retorquing can increase the creepage to the point that the connection fails. Look at this document.
Don
http://www.mikeholt.com/code_forum/editpost.php?do=editpost&p=615212

Don,

Thanks for the article. It was an interesting read.

I have concerns about comment from the article, then --

Is it O.K. to check the torque on a
connection? Absolutely, but any
further action should not be taken
until the condition of the
connection is evaluated.

I don't know how to check torque without possibly turning the set screw. Which says to me that if there's a problem, periodically checking the torque on the connection is the same as periodically retorquing it to slightly less than the original torque. Is there a guideline which says "If the screw moves more than X% of a turn while checking, throw your hands up and start over"? Better yet, "If the screw moves at total of more than X% of a turn since installation, throw your hands up and start over"?

 

[don_resqcapt19]

Tallgirl,
The last part of that article bothers me too, as I don't know how you check. I think that the best check would be a thermal image under full load. Even a little bit of rotation at each yearly check will cause problems at some point.
Don