NEC "Tug Test"?

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cbooker

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Electrical Contractor
We recently completed a Generator installation, and the inspector was pulling on the Generator Feeders wires at the Automatic Transfer Switch until they broke loose. My onsite electrician told me that he tugged on them with both hands at the Transfer Switch until it broke loose at the terminal. He then failed the inspection stating that the wire lugs were too loose for the inspection. The inspector pulled on a Metallic Seal Tight Connection in a similar manner until that broke loose as well and then stated that the seal tight connection was also loose.

I am very familiar with Torqueing lugs to spec based on Manufacturer recommendations, however, what do we do if the OEM torque spec isn't strong enough to resist a grown man tugging on a Seal Tight or Power Feeder Connection? I don't believe there is a "tug test" requirement anywhere in the NEC code book stating a wire or seal tight connection must withstand 100lbs or 50lbs of downward force at the terminal or seal tight connection? Is there something that I am missing here? Any help in this matter would be greatly appreciated. Thanks!!
 
Um, no. IMHO not by any rules is that technique or behavior acceptable. That inspector needs to be reported up the line for damaging the installation, and the site owner ought to consult their lawyer about going after the inspecting organization for the costs to repair.

Torque/install to manufacturer's spec (that's the code requirement); if the inspector doesn't believe you, loosen and torque again while they're watching.
 
zbang said:
Um, no. IMHO not by any rules is that technique or behavior acceptable. That inspector needs to be reported up the line for damaging the installation, and the site owner ought to consult their lawyer about going after the inspecting organization for the costs to repair.
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Couldn't be said better.
 
Hv&Lv said:
Some inspector stupidity never fails to amaze me…
This level of stupidity takes the cake..
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I know of one in Asheville a few years ago that is on the same level of stupidity. He came to a job site where the lightning protection counterpoise was cadwelded and he took a hammer like a madman to random connections, I'm not talking about tapping or even a sharp strike, he looked like a crazed mad man trying to destroy each connection, the idiot didn't even understand that the lightning protection was not under his control.

With the exception of this nut the Asheville inspectors were exceptional and I was lucky to have worked with them
 
zbang said:
Um, no. IMHO not by any rules is that technique or behavior acceptable. That inspector needs to be reported up the line for damaging the installation, and the site owner ought to consult their lawyer about going after the inspecting organization for the costs to repair.

Torque/install to manufacturer's spec (that's the code requirement); if the inspector doesn't believe you, loosen and torque again while they're watching.
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More cowboy inspector behavior.
 
If these facts are true, this should be taken to a higher level for sure. I've seen some pretty bad inspector behavior and competency over the years and this ranks right up there on the list. In any event, I would make it clear this clown is not allowed back on the job site.
 
This is so bizarre. Had a solar crew member tell me that we had an inspector yanking (grab and pull) on feeder wires on a job site last week. And these were LIVE conductors. Is this Covid Brain Damage or what?

My hands GO-IN-MY-POCKETS on someone else's job site -- even if I am doing commissioning or inspection.

cbooker -- was this in Irving?
 
Phil Timmons said:
My hands GO-IN-MY-POCKETS on someone else's job site -- even if I am doing commissioning or inspection.
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I agree. Simple professional courtesy. If someone is on my job site, be it an inspector or whoever, they best mind their Ps and Qs or they will be told to leave. Had it happen more that once over the years.
 
You CANNOT INSPECT for torque after the fact, period. Once you torque TO SPEC that’s it. After that point the metal rapidly relaxes. 50-70% of loading us lost over the next couple weeks and a lot of it is lost in the first few minutes after you tighten. Haven’t you noticed that if you tighten everything first then go over it again it is still “loose”?

At best you can test calibration in the torque wrench. They are supposed to be checked every 1000 uses or so anyway.

There are dozens of ASME specs on this, and the NASA fastener technical manual.

NETA ATS (acceptance test standard) recommends torque testing (which is really an installation standard, not inspection), micro-ohm readings, or IR inspection. IR requires at least 25% load and energized. Micro-ohm varies by manufacturer but as a general rule all connections should be well under 1 milliohm. Unfortunately micro ohm meters cost thousands.

If it’s critical mechanical lugs should not be used. Use crimp lugs with dies that leave a mark. So the inspector can just look at the cable size, the die size, the crimp itself, number of crimps, the inspection hole if it has one to ensure it was fully inserted, and again torque but this time it’s a nut on a stud or bolt. This is the most reliable connection.
 
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cbooker said:
We recently completed a Generator installation, and the inspector was pulling on the Generator Feeders wires at the Automatic Transfer Switch until they broke loose. My onsite electrician told me that he tugged on them with both hands at the Transfer Switch until it broke loose at the terminal. He then failed the inspection stating that the wire lugs were too loose for the inspection. The inspector pulled on a Metallic Seal Tight Connection in a similar manner until that broke loose as well and then stated that the seal tight connection was also loose.

I am very familiar with Torqueing lugs to spec based on Manufacturer recommendations, however, what do we do if the OEM torque spec isn't strong enough to resist a grown man tugging on a Seal Tight or Power Feeder Connection? I don't believe there is a "tug test" requirement anywhere in the NEC code book stating a wire or seal tight connection must withstand 100lbs or 50lbs of downward force at the terminal or seal tight connection? Is there something that I am missing here? Any help in this matter would be greatly appreciated. Thanks!!
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Hey cbooker -- was this in Irving?
 
paulengr said:
You CANNOT INSPECT for torque after the fact, period. Once you torque TO SPEC that’s it. After that point the metal rapidly relaxes. 50-70% of loading us lost over the next couple weeks and a lot of it is lost in the first few minutes after you tighten. Haven’t you noticed that if you tighten everything first then go over it again it is still “loose”?
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I have seen this and always wondered though never looked further.
Does that mean a “250in pound torque” is initially for the compression of the material, and they account for slacking so the final connection is not really “250 in pounds”
Plus if your using copper the compression going to be much different.

Seems unless they have a different value for copper along the the range of final torque value the material will end up at, torque is garbage!!
Unless like you said use crimp on. No one’s going to do that though for a small resi service though.
 
The clamping pressure actually comes from fastener stretch, which is approximately accomplished by tightening until the specified torque is achieved. When you see the plates with all the nuts'n'bolts that connect girders, the strength of the joint comes from the clamping pressure, not the bolts' shear strength.

I would imagine the relaxing that Paul mentioned in post #16 is taken into account when torques are specified for mechanical connections. Otherwise, we would be instructed to tighten in steps, the way we are when torquing cylinder head bolts when assembling engines (which I know also minimizes warping.).
 
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