How can the electrical inspector be sure that the torque at terminations meets the manufacturers instructions?

Is there some method that can be used to double check the terminations?

Using a torque screwdriver would be the offical way to check for proper torque.
I've seen some inspectors check for connection tightness by pulling on the wire. Other inpsectors use a screwdriver to check for tightness and not torque.

[This message has been edited by Mike (edited 07-11-2001).]

I don't think there is any way that the torque can be checked by the inspector. I have been taught that it is never correct to re-torque a connection. If an inspector would use a torque wrench to check the torque he would be re-torqueing it. The torque specs that are issued by the manufacturers allow for the "cold flow" or relaxation that will occur after the connection is made. The manufacturer's listed torque will provide the proper contact resistance even with the heat cool cycles that will occur with varying loads. If a connection is re-torqued it may become too tight and result in a poor connection at low loads. This would happen to a connection that has been re-torqued and then subjected to a full load. The full load will cause some heating and expansion resulting in additional cold flow. When the load is removed and the conductor cools, the connection may have a higher resistance then it should have. This problem occurs more with wire connections, than with bus bar connections.
A conductor that exhibits evidence of overheating at a termination should be cut off and re-terminated, not just re-torqued.
Don(resqcapt19)

What ROP is it that will boost tourqe wrench stocks anyway?

We've got a couple of jurisdictions here that the inspectors actually hover over you while you make up connections. If they've been tightened before they get there, they'll make you remove the wire and start over.

electure,
Do they make you cut it off first? This would be about the only way that the torque could be verified, but it would sure be a problem having the inspector there when you are ready to terminate.

sparky,
110-3(b).

Don(resqcapt19)

I've got torque wrenches & torque screwdrivers for my own use, but when I do an inspection, I usually don't use them, mainly because I might become liable for any failure of the connection. However, I did run some experiments & found that the average electrician will stop at a value that is about 20% to30% below the listed torque. This was especially noticeable with Square D breakers up to 30 amp.

I know that there is some bus duct that has dual headed bolts, one head snaps off when the proper torque has been reached, maybe some day we'll have the same thing for the rest of the electrical connections, if we can afford it.

I think Don has the right idea about not re-torquing the connections. But, if you had a lot of patience, you could start with a low value & slowly keep adjusting up.

Tom

[This message has been edited by Tom (edited 07-11-2001).]

Anyone know of a "cheap" torque wrench and torque screwdriver?

I priced a Klein Torque screwdriver and was surprised to fine out that a sawzall is cheaper... heck, a Milwaukee Sawzall is cheaper...

Can't seem to find a torque wrench that measures in-lbs, only ft-lbs.

I'd considered about $50 to be reasonable...

>you could start with a low value & slowly keep adjusting up.
You wouldn't detect over-tightening.

And if the circuit had been energized and heated up at some point, you might over tighten it.

Don.
Yes, they make you cut the end off of the conductor, restrip it, and reconnect it.
They tell you when you pull the permit that the torque insp. is a requirement(via red rubber stamp on approved prints), and if you don't pay attention, S O L, even if it's 1000 MCM. It's only in a few cities.
. The unfortunate part is that in 1 town, the inspector didn't know how to convert from "/lbs to '/lbs.
Most cities only require a letter from the office, stating that you've torqued it to the manufacturer's specs.
Virgil,
. Home Depot(yeah, I know, everybody hates 'em) Husky "/lbs. (from 25 to 250)
about $40. The torque screwdriver is a pain in the $. Napa.

[This message has been edited by electure (edited 07-11-2001).]

http://www.necdirect.org/pdfs/A110.pdf
log# 2048, pg 4

i really can't take this seriously

Tom,
Even if the connection has not been energized, you will find that the head will turn before you reach the specified torque. This is because there is some "cold flow" of the conductor bewtween the time it is installed and when you test it.
Don(resqcapt19)

Sounds to me that there should be a rate-of-time factor involved... if you torque it down (hypothetically) with a pneumatic tool, or very slowly with a torque wrench, that the integrity would be compromised between the two extremes of speed due to friction / temperatures affecting the calculations that the manufacturer's used to get their numbers. (Whew!)

Any comments?

Just how exact of a science does this have to be?

Sparky,
If this isn't already covered by 110-3(b), I think it should be.
Hey, does anybody put Noalox on the lug's screws to stop that squeaky-squeak,jerky-jerk? I do, and I think I get a closer value by doing so.




[This message has been edited by electure (edited 07-11-2001).]

electure;
well.... believe it or not, No-Lox is a listing requirement of some service equipment.

and the tourqe thing, the intention is good, don't get me wrong. it's just that there are a multitute of variables here that a torque wrench will not address, so to me it's a very generic 'fix' . As Virgil and Don's posts eludes to, the physical characteristic's involved are fairly deep. My point of view is tainted by having to work with engineers for a decade who would probably have a 3 day pow-wow resulting in a mini-series , such is mil-spec!

In the practical world , think of all the torque requirements that could apply here, as we seem focused only on service gear;
-every switch...
-every receptacle...
-every wirenut...
-every pipe fitting...
-every lug, bug...
no one , other than an extreem obsessive/compulsive individual is going to actually use a tourqe indicating tool on all of this

yesterday's observation;
Siemens now makes a 'speed-screw' panel. This has Grn/Noodle bars with combo square drive heads. The installer can now use a bat-drill to drive all these home, it really works well, and as i was doing so i wondered if the clutch settings could be translated into inch-pounds

And to add, how large of a window is the margin of error?

Does 250 in-lbs torque mean not 249.9999999 and not 250.0000001, but 250.00000000 ????


Clutch settings torque... Great idea!

[This message has been edited by sparky66wv (edited 07-12-2001).]

Hello Bob: I am in Kansas and one of your former grounding students Dan Deneault was trying to remember your method of checking the torque at termination's? Can you help here?

Joe

Answer: Well Joe ... as an inspector you'll want to see if the torque requirements have been met. What I do is set my calibrated torque wrench at 15% below the torque setting used by the installer. If I get movement then it's a failed connection that requires correction. This way I'm not altering the installation.

Once the installer knows you will be checking then, as if by magic, this torque requirements are met.

Is funny how this happens on a job.

Say HI to Dan ... Bob N

>Clutch settings torque...
They do represent torque. But they vary from machine to machine. You can use your torque wrench to find out what setting slips the clutch. It might be 9 on one tool and 18 on another for about the same inch-lb torque.


Too bad the drill manufacturers don't just calibrate the clutch in recognizable and standard units right from the factory.

>how large of a window is the margin of error?
I would say at least 10%. 250 is 225 to 275.

But if the inspector is checking, I would say 250 means 250 to 275.

Virgil,

One of my torque wrenches is from Sears, goes to 250 lb/inches and I think it was under $50.

Tom

Joe,
Does Bob have any technical data that says the cold flow effect will produce less than a 15% torque change?
Don

Joe, I knew you would email me before I got to the office this morning. I was in Joe's class (Understanding the Basics of Building Electrical Inspeciton) this week and asked the guestion, "How does one check to see if an electrical contractor torqued a termination to the manufacturers' specification?". I remembered that Bob Nolan (from my Grounding and Bonding Seminar) had made reference to a method, but I could not remember the method completely. Joe suggested that we try the website for comments. Thanks everyone for the insights you gave me. Bob, responded with his answer in the form of an email which Joe sent out to all respondents last night. Again, thanks. Joe, I have registered and look forward to many more discussions like this.

Don: no technical data, on this job the electrical engineers, contractor and myself agreed to the 15% as the torque inspection would be done about 1 hour after the installation. The system was new never energized, the torque was on bolted lugs with copper conductors, and the temperature in the area was contolled.
No one felt cold flow, thread lubricants, or differences in wreaches as something that would effect the installation or my inspection settings.
After inspecting 1100 plus terminations everyont felt the process was OK.

Bob,
Thanks. I was just wondering if there was any published data for this. I know that even without loading and temperature changes there is some cold flow over a period of time that will allow a partial turn before the original torque is reached when you check the torque. I don't think there would be much change in the one hour time frame that you were working with, but wonder about how much change there would be after a week or two.

Don(resqcapt19)