HELP! Re-torqueing Connections

[brian john]

White knuckled bug eyed monkey torqued.

NICE PHRASE may have to borrow this.......

 

[Smart $]

Jim,
I think you and Zog are talking about different types of connections. I think he is talking about things like bus bars or a wire terminal connection to the bus bar or breaker. I believe you are talking about a mechanical wire termination where the screw you are re-torquing applies direct or indirect pressure to the conductor itself. It is my understanding that the second type of connection should never be re-torqued.

Exactly, that is what I posted before and am trying to explain now.

Point in fact, however, the reason for not doing it to the latter type contradicts the reason for doing it to the former. In both cases, the text highlighted in red is what is being done.

Generally we are talking of an electrical connection made by mechanical pressure through or by means of differing materials. It is the differing materials which present the problem, in that they expand and contract by different amounts under the changing temperature conditions experienced. If the connections where made up entirely of the exact same material, the need for retorqueing would practicably be eliminated.

The above is not meant to imply connections should never be retorqued, rather that simply retorqueing connections is not a wise course to follow. The following excerpt is from Burndy's Connector Theory and Application, A Guide to Connection Design and Specification. Refer to page 28 of the publication for the entire contextual meaning and recommendations.

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.

 

[iwire]

The focus seems to be the affect of re-torquing on the material being fastened.

Let's not ignore the adverse effect on the fastener itself. For example, head bolts on a racing engine are never re torqued, not because of clearance with the head or gasket, but because the fastener deformation is calculated into the torque value. Further retorquing goes out of the engineered range of the fastener.

Jeremy I understand what your are saying but I think we have a different situation. As you said with a typical situation on a motor the published torque specs are high enough to stretch the fastener. The fasteners in an engine are used to their ultimate strength.

On the other hand with electrical termination the actual threaded bolt is only tightened to inch pounds or low foot pounds and does not distort the fastener only the conductor under it.

 

[jrannis]

I have a habit of checking residential breaker terminations when I have access to the interior and am surprised to find that I can get at least 1/2 or more turns out of most screws without much effort.
I always torque larger conductors to the value listed on the equipment and put a witness mark on the terminal.
I wouldn't consider "re-torquing" , could probably get a quarter turn every week until it was destroyed.

 

[dcspector]

White knuckled bug eyed monkey torqued.

Sweet.......I love it!:smile:

 

[ItsHot]

conductor scans

conductor scans

I thought one of the reasons to do infra-red conductor scans was to determine loose connections that may need re-torquing.

 

[jim dungar]

Jim,
I think you and Zog are talking about different types of connections.

That is why I said in my post cable connections.

If you read articles on quality assurance and checking torque settings you will find that there is no good way to have a non-expert use a torque wrench to verify that torque is within tolerances. If you use a non-beam type of torque wrench to retighten a connection it will give usually give you a false positive, this has to do with the static friction of the fastener. If you continue tightening until the connector breaks away and then stop once movement has begun you will typically overshoot the desired setting. This is a QA quandry when your tolerances are tight, but most electrical bus bar connections I have seen have fairly loose tolerances.

 

[Pierre C Belarge]

On the other hand with electrical termination the actual threaded bolt is only tightened to inch pounds or low foot pounds and does not distort the fastener only the conductor under it.

Bob
The values you posted are valid only if one is actually using a torque tool.
The majority of terminations today are not properly torqued. A lot of the terminations are over torqued....which can and does lead to the terminal becoming distorted and even cracking. This type of damage can only be corrected by removing the damage terminal and replacing it.

I thought one of the reasons to do infra-red conductor scans was to determine loose connections that may need re-torquing.

That is one of the reasons for infra-red testing, but there are other factors involved in overheating, and one of those is what I posted above.

 

[acrwc10]

Bob
The values you posted are valid only if one is actually using a torque tool.
The majority of terminations today are not properly torqued. A lot of the terminations are over torqued....which can and does lead to the terminal becoming distorted and even cracking. This type of damage can only be corrected by removing the damage terminal and replacing it.



That is one of the reasons for infra-red testing, but there are other factors involved in overheating, and one of those is what I posted above.

Just last Thursday I watched the POCO not use a torque wrench to land their service lateral into a 400 amp panel/meter. When I used the words "Torque Wrench" you would have thought I was speaking in a different language.
I find it interesting that they will not torque down the lugs, but if it fails they will make the home owner pay for a new panel (because it is their panel not the utilitys panel)