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

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).]