ECN Forum Forums Code Related Discussion NEC & other Code issues Torque

iwire & capt al ---

Because I have no knowledge as to how far outside specs (if any) others tighten their fittings, I will not address problems that others may have with circuits under 200amps.

I have given 3 methods of checking torque. I don't see you offering a method to check torque.

I have not offered one because there is no way to check torque short of being there while it is being done.


This does not check torque, this only ensure torque has been reached, it does not tell us if torque has been exceeded.


I agree with Method 2


I agree this will work but the application is limited and it will be a problem if a you have disconnect and reconnect a conductor.




[This message has been edited by iwire (edited 06-25-2005).]

Just ask "Can I see your torque wrench". If he can find it he probably used it. If it is buried "somewhere in the truck" or back at the shop he probably didn't ;-)

George, I wish I could follow your logic. First you say:
I believe the picture iwire posted for me shows long term damage on phase "A" Maybe I'm wrong. I always thought the insulation splitting off a conductor due to overheating was a bad thing. This connection was out of torque. According to you wrong torque is no problem. Look at the picture again if you want to continue believing torque is not an issue under 200 amps on copper conductors.
The picture shows a 480 volt 100 amp disconnect switch for the emergency smoke exhaust fans in a warehouse. The only time these fans have ever ran was when maintenance tested the system quarterly. The fans do not have much run time so you can see what an under torqued connection can due in a sort period of time.

Second: Lets forget the "others". Do you torque? As you can see from the posted picture torque does matter under 200 amps!

Third: How about Infrared Testing your connections after installation. This is not a cheap way to verify torque. I have done this for an EC because in was in the specs for the job. He would get no final payment unless an IR report was submitted.
Al




[This message has been edited by capt al (edited 06-26-2005).]

OK, I'm in on this one.....

Heads breaking off when torqued properly?
How do you get them off, if the heads break?

I mostly use crimps on anything over 8Awg stranded, no problems with torque and or conductor damage.

George, you as an engineer should already spec out the use of crimp connectors, the use of mechanical lugs should not be used IMO.

No having said that, when using solid conductors in say a resi panel, I doubt there is too much damage to soild conductors as one might expect. But I am sure it happens, when you tighten it like a gorilla.

"Tight is right", loose connections make heat and arcing.


Just my thoughts...


Dnk..........

They are double headed bolts with a machined area between the two head that is designed to twist off at the required torque.
They also make hex keys that work the same way. They are a "one time" torque tool. You insert the tool in the hex socket on the lug and use a socket wrench on the other end of the tool. It snaps at the correct torque.
Don

[This message has been edited by resqcapt19 (edited 06-26-2005).]

I don't know about the rest of you but my torque ratchet handle and my torque screwdriver are made to "break away" when you reach the preset torque value. I have seen and used torque wrenches that "click" when you hit the setpoint but allow further tightening beyond the "click". My tools will not allow you to go beyond their setpoint. I can use them to see if a value has been reached but I cannot tell if the value has been exceeded.

capt al ---

I am sorry. I was too brief. I only work on systems under 200amp and 240volt. (I would not have enough work at higher power or voltage to keep up the necessary skills.) When I say torque is not important, I mean not as important as some seem to believe. In particular not important enough to require a torque wrench on any connection I make.

In your photo you make the assumption that the initial torque was wrong. I did not do the work. So I will again not comment on the work or the cause of the problem.

While IR testing is better than torque verification, the requirement is torque not performance. I would accept an IR test.

I torque with my battery powered drill with an adjustible clutch. (I use the numbers for repeat settings.) For terminations 30amps and below I know what setting provides a good connection. For teminations 35amps to 200amps I do tests with scrap wire until I am happy with the appearance of the connection. (I check the appearance by disassembling the connection.)

For work over 200amps or 240volts I sub the work out.

Let me guess and say I'd bet that pic that shows the broken insulation was under torqued not overtorqued. I doubt cold flow had anything to do with it. If you forget to tighten a connection does a torque wrench make any difference??

Fred,
You just can't use any type of torque wrench to check the torque of an installed electrical connection that directly involves a conductor. Checking the torque on the bolt that holds the lug to the bus or bus bar bolts is ok, but checking the torque on a conductor termination should not be done. The connection relaxs and you will get some additional movement if you use a torque wrench to check it. Once probably won't hurt anything, but some places do this once a year and that will cause problems because the conductor will be damaged.
Don