Milbank Torque issues 400Amp

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florida-sparkey

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Location
Pinellas Park, Florida
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Master Electrician
I have been having issues with the meter touques on the 400A enclosures.
I was certified and built engines professionally so I know my way around a T wrench. My T wrench is high end, calibrated, digital and appropriately sized for the torques involved.

The enclosure label states the nut mounting the lug to the stud is 200 Inch pounds. That seems low to me for a 3/8 stud.

The enclosure label states 500 inch pounds for the wire sizes we are installing. That seems way high and far exceeds the NEC recommended 250 inch pounds for same size . As a reference- The same lug measured across the flats, for the same wire on the breaker side is labeled to be torqued at 250 inch pounds.

So the problem is that the low torque lugs (200 inch pounds) want to spin on the stud before the terminal gets to spec and the allen key feels like it wants to stip out out at the high torque (500 inch pounds).

Have I made some kind of mistake? Label seems easy to read, I have checked multiple enclosures looking for a mislabel.
Still, are the labels possibly incorrect?
Anyone else have this issue?

I have stopped even trying to bring the wire connections up to 500 in lb. Experience tells me something is going to break. I have stripped out the inside of at least one allen key.
 
I have had issues with torquing terminals where the single hole type terminal, bolted to a bus bar, will twist with the correct torque.
I suspect that the typcial resi electrician does not use a torque wrench. Does it make a difference if the lug is lubricated>
In my Navy Nuclear Power days, we always used calibrated torque wrenches, calibrated within 90 days, and lubrication of the fastener was a must
 
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This whole business of specific torque values has always perplexed me, especially in larger stranded sizes. The values seem a fallacy to me as it is like torqueing a sponge. If you torque, say, a 250 conductor into a typical listed lug just moving the conductor to dress things out completely changes the value. And with the typical range of approved conductor sizes for a given lug the results vary wildly. After all, electrical connections are not precision surfaces like in, say, an engine head.
 
tom baker said:
I have had issues with torquing terminals where the single hole type terminal, bolted to a bus bar, will twist with the correct torque.
I suspect that the typcial resi electrician does not use a torque wrench. Does it make a difference if the lug is lubricated>
In my Navy Nuclear Power days, we always used calibrated torque wrenches, calibrated within 90 days, and lubrication of the fastener was a must
Click to expand...
I have not tried to lube the lug threads but the listed torque still seems way to high to me.
 
tom baker said:
Yes the tightening instructions should state dry or lubricated
Click to expand...
  1. And if it is not stated, my expectation is that for a typical electrical equipment environment where adding lubrication is not common, the torque value would be unlubricated. An exception would be a connector which has been prefilled with a water repellent like silicone grease.
  2. In my experience, unlike engine fittings, wheel studs should never be deliberately lubricated. For two reaons, that they are more likely to loosen in use if lubricated and that the specified torque is the dry value.
 
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