Section 110.14(A)

[don_resqcapt19]

Re: Section 110.14(A)

Bob,
This source says connections should never be "re-torqued". It does say you can "check" the torque, but I don't know how you can do that without "re-torqueing" the connection. Maybe if you check within a few days or weeks of the initial installation it would be ok, but beyond that, it is my opinion that the conductors will have been compressed enough so that you will get additional movement on the set screw. This will result in an "over-torqued" connection.
Don

 

[rbalex]

Re: Section 110.14(A)

Bob (iwire) and Don.

One of the real disadvantages of my career is that, while I have a fair amount of installation experience, I have virtually no direct maintenance experience. I?ve certainly seen the results of poor maintenance and have been involved with a few product liability / system design (not mine ) lawsuits where both maintenance and initial installation were at issue. None of them had anything to do with torque though.

This is a typical excerpt from NFPA 70B:

Chapter 9 Motor Control Equipment:
9-3.2 Loose Connections.
Busbar and terminal connections should be inspected periodically to ensure that all joints are properly tightened. Proper torque is a function of bolt size, bolt type, terminal material, washer type, and type of busbar. Proper bolt torque values for all types of joints involved should be available in manufacturers? maintenance and instructional literature. It should not be assumed that busbar and terminal hardware, once tightened to proper torque values, remains tight indefinitely. (See Section 18-16, Infrared Inspection, which describes one method of detecting loose connections during the periods between shutdowns.)

I can?t do a ?cut and paste? of my NEMA documents but several of them are available as free downloads here . Do a ?find? on ?maintenance,? and get a copy of PB.1 or 2 as an example. Other ?maintenance? documents are also available. They make similar statements; e.g., NEMA-PB.1 Section 10, Paragraph 10.4.2.

I don?t know which FM document is cited on Don?s referenced site. I do know both the NEMA and NFPA documents I mentioned are ANSI sanctioned, which technically makes them enforceable by FedOSHA?s ?general use? clause. I also know the FedOSHA enforceable FM standards are relatively limited ?product? standards listed here.

All that being said, I think your experience is still valid. I have no unique knowledge of any torque requirements and manufacturer?s instructions vary. Some may say do nothing at all in absence of ?visual? evidence of over heating. NFPA 70B suggests infrared inspection. My point is you must know what a manufacturer?s torque instructions are to properly install/maintain equipment and it is as reasonable an addition to NEC mandatory text as 110.14(C)was.

 

[don_resqcapt19]

Re: Section 110.14(A)

Bob,
I have no problem with the re-torqueing of the busbar bolts or the bolts that connect wire connectors to the busbar or other equipment. The problem is when the set screw that holds the wire itself in place is re-torqued. PB1.1 and 2.1 both specify tightning bolts at bus joints, not the wire connector itself.
Don

 

[rbalex]

Re: Section 110.14(A)

Don,
I am happy to acknowledge, at least one terminal/connector manufacturer specifically agrees with you :

It is often asked whether bolted connections require periodic retightening. The simple answer is NO. Once the connector is installed with the proper torque, repeated tightening could actually damage the connector and/or the conductor and eventually lead to a failure.

There is some other very useful material there too. It discusses a whole theory of "connections."

My point has always been one needs to know the manufacturer's instructions, not whether re-torquing is a good general recommendation. Essentially even the standards I referenced say "ask the manufacturer."