I've got a Klein torque screwdriver on order, how do I find out the torque specs of various and sundry equipment?

No problem on service equipment and CB's, it's plainly written on a label in the enclosures somewhere and on the CB's themselves...

But switches and recepts are another matter... Nothing on the boxes or devices themselves that I've seen...

Any help?

[This message has been edited by sparky66wv (edited 06-17-2002).]

The only torque specs for a duplex receptacle that I could find was on the Leviton web site (www.Leviton.com). This is the statement from their spec sheet for the 5262-IG Receptacles –
Designed torque capability of +20 inch pounds.

You have torque figures marked on some devices these days??! Wow!

I have to work to the principle: If the screw head shears off, it's too tight.

Sparky66
I have had mine for about a month now and Dont leave home without it.
In fact there is a list of torque specifications in the code. On Hubble receptacles they recommend between 9-12 in-# or 1.0-1.4 N.M
I found that the screwdriver is invaluable especiallly doing services, and it amazing how much you over tighten things, especially devices .
I usually use Siemens and for the smaller breakers 15-50 they recommend 24 in-#, and on all the liturature inside the cabinent it list tightening torques.

Paul of the UK
On the Siemens Breakers its right on front cant see it without a magnifier or lots of light, but all the manufactures have a torque specification, Square-D recommends I think 35in-# for its breakers.
Anyways I am sold on it.

I like your priciple, thats sort of like the one that states, Tighten a screw all the way down til it wont go any more, then one full turn.
-Mark

[This message has been edited by motor-T (edited 06-19-2002).]

[This message has been edited by motor-T (edited 06-19-2002).]

Thanks for the replies!

So, now I've had my torque screwdriver for a couple of services, and a torque wrench too.

The service I put in last week was the first I had installed "properly" using the torque specs listed in the panels and on the CB's. I have been over-tightening the lugs (250 in-lbs), busses and breakers (20 to 30 in-lbs), and probably not getting the EGC and range wire neutral tight enough on the bus (35 in-lbs).

However, upon inspection, the inspector breaks out his 3/8" allen wrench and procedes to tighten my work another quarter of a turn!

Plus he said that he likes to see the slots and edges buggered-up so he can tell I got 'em tight enough. I explained that I had torqued them to specs, (and had spent $130 on a screwdriver and $85 on a wrench so I could) and I didn't really think it was good to retorque terminals. (You'd eventually cut them in two, wouldn't you?)...

After a glare or two, he replied "they loosen up anyway..."

And I left it at that.

At least this inspector quoted 250.66 to let me know that I "could've" used #6 for the EGC instead of #4 if I had wanted.

Monday I have another inspection with another inspector.

How do I convince him that "I've torqued to specs and please don't touch my work" in a nice way?

Sparky,
OK, the guys an idiot. You DON'T overtorque. Make little black checkmarks on the bolts that you torque as you torque them. If the inspector knows anything, he'll recognize that as tester marks.

Um... Interesting story I had forgotten about:

The Inspector I'm using on Monday has at one time broken a lug on the meterbase checking the "torque"... I think he learned his lesson that way, but I still wonder if he understands the whole issue like you gurus do...

Maybe if I could explain in a scientific way why it is bad to overtorque and re-torque, my argument would have more weight.

George, may I trouble you (or anyone else) for a deeper explanation?

[This message has been edited by sparky66wv (edited 07-04-2002).]

"...inspector breaks out his..." WTF? A building inspector modifying others’ work? What a d!pshit. Do his superiors know about this behavior? {The felt-pen marks are a good idea.}

Maybe the next time he'll tear out all yer #12 and replace it with #10.

The guy reminds me of some pathetic dad in the bleachers at little-league games who yells at coaches and umpires about his kid, trying to make up for his own twisted victimization in childhood.

He must have failed miserably as a tradesman and is now self appointed to compensate for all the shoddy workmanship he perceives. {Some loctite in setscrew threads may cause him to eventually loose interest in sainthood.}

He could get suicidal if you set up a pull section with ½-inch 2-bolt hydraulic-compressed lugs and bellevilles, or, better yet, 5/8-inch dragon-tooth washers.

Many thanks to Joe T. and George C. for sending me various and sundry torque specs as I requested... Great! I've got the tools and the specs, now I need the "theory" to back me up...

Let me ask a few Q's to let you know what I'm looking for now:

If/when the inspector or any other "authority" has the opinion that torquing to specs isn't tight enough, and claims that the terminals loosen up anyway, and later need re-tightened (read: retorqued)... What the heck do you say to them?

What happens to properly torqued lugs over time (Especially with Aluminum Conductors)?

What happens to an over-torqued lugs over time as compared to properly torqued lugs?

What happens to re-torqued lugs over time as compared to properly torqued lugs?

What happens to under-torqued lugs over time as compared to properly torqued lugs?

When I'm out in the field trying to give my viewpoint to those who disagree, I tend to give the impression that I'm "hung-up on code" to the point of being unproductive, but yet when I'm here on ECN, I have the feeling that I'm on the other end of the spectrum as a jack-leg weekend-warrior compared to you "heavy cats" (musical term, it's a compliment...).



Either George or Watt Doc, or somebody here once said: "The problem with electricity is that it almost always works."

Boy, is that ever right.

Note these comments refer to mechanical wire terminations and not buss bar connections or connections between a wire connector and a buss bar. The materials involved in these connections are harder and do not behave in the same way as wire.

All torqued connections relax over time. This relaxation is accounted for in the original torque spec.

If the connection is too tight, the wire has more "cold flow" and is extruded out of the connection. This is made worse with heavy cycling loads where the heat causes the wire to expand and produces even more cold flow. This will in some cases eventually result in a high resistance connection and failure.

In my opinion the same effect happens when wire connectors are retorqued as when they are over torqued.

Under torque also will result in a high resistance connection over time. With an under torqued connection, excess heat is produced at the connection and the wire expands causing cold flow and as this cycle repeats the connection get worse and at some point it will fail.

I was taught never to retorque a connection. If the connection is showing early signs of trouble, the wire should be removed from the connector, cut off, stripped and installed in a new connector with the correct amount of torque.

Don

Thanks Don, that was what I needed... Good ol' physics explained in laymens terms... Right up my alley! And thanks for clarifying about the busbar thing too... How do they differ? (If ya don't mind 'splainin' some more...)

Thanks again...
-Virgil

Wait... I just realized what you're saying...

The guys who over torque are finding their connections to be loose later because they are over torquing them in the first place! And my properly torqued lugs won't loosen as badly as theirs, and they think that mine have a "head start" on being loose...

Wow... An epiphany!

Think of it this way........ The threads are 'basically' a triangle observed from the side, they are designed (by what type of metal they're made from, and what their Rockwell hardness # is) for a certain stress.
Understress, it's not tight enough, in other words, it's already loose, and the problem ain't getting any better with the cycling Don mentioned.

Overstress, and the shape is malformed and no longer mates with the lug, leaving voids and eccentrics, THAT usually loosens quicker than an undertorque.

I've got some literature on WHY it is improper to retorque after proper torque has been reached, but I may have to wait until Monday, and I'll talk to our testers to see what they've got. This stuff is a lot more "official" than just putting it here, so if I can find it (I'm pretty sure I can) I'll pass it along.

One term for an overtorquing effect is "coldflow;" or the tendency for the conductor to "ooze" over time. Copper is not exempt from this characteristic, but it less sensitive to it.

For aluminum, it's important to call for "AA-8000" conductor alloy, [99NEC§310-14] which is compounded with a small amount of iron in the recipe. Be aware that not all aluminum insulated conductors are automatically 8000 series. Type USE cable is permitted to still be formulated of “EC-1350” alloy, as may also be utility-furnished 600V URD cables.

IMO and experience, nonreversible hydraulic-compressed terminals are the only sure bet. They just take a little more planning.

Out of a complete fluke, I was inadvertantly delivered two in-lbs torque wrenches, Sears Craftsman. I was charged for both and the local Sears cannot take it back, I have to send it back to Chicago via $$. They'd probably give me a refund for the postage too, but I figured I'd print this thread out and try to sell the extra one to my partner, Joe Musser.

We'll see...

Fate?

Interestingly, I called Leviton and their Rep told me that all of their standard devices with screw terminals are listed at 12 in-lbs...

I said: "Man that's light!" And he said, "Yes sir, 12 in-lbs."

(Oh, and Joe kept the second torque wrench without any prodding at all!)

the 'machinist's handbook has some interesting stuff on threads thier applicability,
apparently not all are created equal....

i don't know how all this fits in with those new seimens speed-screw terminations .....?

From an engineering standpoint torque is a poor measurement.

If we wrap a wire 360 degrees around a screw and tighten to a specified torque, we have 1/2 of the load (#/sqin) on the wire then if we wrap the wire 180 degrees around the screw and tighten to the same torque. Thus we reach the elastic limit (cold flow) at different torques based on the uniformity of our wrapping.

In the case of plate clamps (backwired devices, large breakers) and ground/neutral bars there is more uniformity in the clamping area and there the torque is more reliable.

-----

Don't confuse the torque numbers used in testing with torque specifications for instalation.

Have fun with your toys.

If torque is not specified, UL has defined a "default" torque for various fastener sizes. Maybe someone can come up with a table?

George, see the test marks?




No problem with retorque on this one!

Great advice, Thanks!

Virgil,

I'll be glad to do your inspections & you can count on me to not mess with your work. I figure with travel & mileage to Pocohontas county, I should be able to do an inspection for about $450. What do you say?



BTW, if you have an older NEC handbook, 1996 for instance, there are some recommended torque specs in article 110. These are the values that UL was using at the time if the manufacturer did not specify a value.


Tom



[This message has been edited by Tom (edited 09-18-2002).]

'66wv — I'd heard a rumor that Sanford’s {the ‘Sharpie’ folks} just bought out an old torquewrench manufacturer, but your picture is the first evidence I'd seen of it...

Gnarley!

Sparky,

If the inspector touches your work, get his name and then write it down inside of the meter pan, etc. Write "This panel was tighten by Mr. AHJ on this date." When he asks you why you did that, tell him, in case something goes wrong, I want everyone to do who did the work. That might stop him. I would never touch anything that an electrician did, then I would become responsible.

One inspector I had used checked every terminal. The problem is that he finds lots of loose ones and how else do you check? (DIYers)

The inspector I used for this one had actually broken a lug in a metercan before (not mine). I think he learned his lesson then, but at this inspection he said he wanted to "gather his tools" and I informed him that everything was already open for inspection and torqued to specs.

I think the test marks drove the point home.