Torque Buss to Lugs

[Shane Williams]

Hello.
Recently I witnessed craftsmen being allowed to connect the lugs to buss without torquing them. Just tighten and go. Yes, I stopped this process and explained the reasoning behind a proper torque to prevent bowing the lug and allowing the possibility of creating an eddy point for heat and failure. I can't seem to find any articles that support this theory of an eddy being created. Can anyone point me in a direction or provide a link to something that supports this? Or have I been misinformed all thru my career?

 

[don_resqcapt19]

The torque for a lug to bus connection where both are solid materials is based more on not getting close to the yield strength of the bolt than anything else.

There are tables for typical bolt torques for electrical connections that can be used, but it is my opinion that the torque of screw in a mechanical connector that puts pressure directly on the conductor stands is much more important than the torque of a bolt connecting a lug to a bus.

I do have concerns where the hole in the bus is larger than the hole in the lug, as that could lead to bowing of the lug, and less contact area between the lug and bus, resulting in a hot spot.

 

[Fred B]

It seems simple At least from the 2017 code, the reference requiring torque found in Article 110.14(D). It implies these specifications may be on the equipment or the instructions, and must be done by a calibrated torque tool or other means stipulated by mfg. So it would seem to me just tightening willy nilly would be a violation.
Now as far as reasoning for what complications can result from improper torque idk, I know on an engine uneven torque on the head bolts can cause warping and engine failure, so it seems that loose or uneven torque could result in other breakers making poor connections because of warping caused by uneven heating of buss due to loose or uneven torque.