Reusing Bolts for Terminations

[Pierre C Belarge]

Fastenal has a technical guide discussing fasteners on their site, it can be found HERE.

On page 29, there is a discussion about reusing fasteners. As I was reading this, my mind drifted back to some of the installations I remember doing over my career in the field. I remember being taught when I was an apprentice using a pipe to extend the length of a wrench to tighten bolts.
I can only guess the damage we applied to those terminations. In our discussion about torqueing, I could not stop thinking how the wrong application of torque, type of bolt, etc...really leads to a pretty poor connection.

 

[Pierre C Belarge]

This is from the Fastenal Technical Guide.

"One important factor to remember; typically you will not know whether or not the fastener has been yielded. Especially in critical situations, you should never reuse a fastener unless you are certain the​

fastener has never been yielded."

 

[cadpoint]

That extension just gives you leverage or Force, the torque is perpendicular, or to say a straight line off of the Bolt and not what your thinking.

Torque is the tendency of a force to rotate an object about an axis (or fulcrum Lever or pivot).

Just as a force is a push or a pull, a torque can be thought of as a twist. The symbol for torque is tTau
(Tau is the 19th letter of the Greek alphabet. In the system of Greek numerals it has a value of 300. This letter in English is pronounced , but in Modern Greek, this letter's name is pronounced Tau ....)

http://www.absoluteastronomy.com/topics/Torque

I've seen this discussion before and thought I'd answer that one (old)but didn't after I refreshed up on it, But with your application of an extension it just required less force to do the same thing... but it's about the axis not quailfied by the length of a an additional arm...

 

[quogueelectric]

Very rare that a seasoned mechanic will over torque a bolt to failure. Most applications are met with quality control of just how important this connection is.
More QC more money spent on torquing properly and documentation. I have found a very small concern for this to happen yet an infrared testing contractor may see much more of this oh so close to failure yet not there yet . How much is the QC worth exactly in dollars and cents??
IT is nice to view the bolt mfgs position on this yet it is predictable cya language. Thank you for the insight Pierre!

 

[iwire]

This is from the Fasten Technical Guide.

"One important factor to remember; typically you will not know whether or not the fastener has been yielded. Especially in critical situations, you should never reuse a fastener unless you are certain the​

fastener has never been yielded."

For at least 99% of our work making electrical connections we will never come close to the yield strength of the fastener.

The torque ratings we use for electrical connections are aimed at making a good connection they are not aimed at bring the bolt to the yield point like we would if where building an engine or say bolting the seats onto a roller coaster.

If we tried to bring a steel bolt up to it's yield point on say a copper to copper connection or AL to AL connection we would start crushing the softer metals.

The use of belvue washers is another reason we do not torque as tight as mechanical type connections.

 

[quogueelectric]

For at least 99% of our work making electrical connections we will never come close to the yield strength of the fastener.

The torque ratings we use for electrical connections are aimed at making a good connection they are not aimed at bring the bolt to the yield point like we would if where building an engine or say bolting the seats onto a roller coaster.

If we tried to bring a steel bolt up to it's yield point on say a copper to copper connection or AL to AL connection we would start crushing the softer metals.

The use of belvue washers is another reason we do not torque as tight as mechanical type connections.

Belleville washers............ Required on all padmount poco connections by me.

 

[Pierre C Belarge]

For those who are actually installing terminations with a torque wrench, I agree that this is not an issue. For all others, how much force is actually being applied can only be guessed at.

 

[LarryFine]

The use of belvue washers is another reason we do not torque as tight as mechanical type connections.

Belleville washers............

I like Belvue washers, for those of us who are going crazy.

 

[brian john]

I have seen on one occasion bolts over torqued to the point of failure. During a battery load test 1/4" stainless steel bolts failed on the initial current draw. Made for quite a mess and scared me almost to death as I was performing an IR scan of the connections during discharge,


The EC was asked for his torque wrench he had 2' of black iron and a 1/2 breaker bar. We were hired to replace ALL the hardware they torqued.

We had furnished as part of our contract torque wrenches for the EC along with instructions and torque values, he said he felt uncomfortable with such loose connections.

 

[iwire]

For those who are actually installing terminations with a torque wrench, I agree that this is not an issue. For all others, how much force is actually being applied can only be guessed at.

I have seen on one occasion bolts over torqued to the point of failure. During a battery load test 1/4" stainless steel bolts failed on the initial current draw. Made for quite a mess and scared me almost to death as I was performing an IR scan of the connections during discharge,


The EC was asked for his torque wrench he had 2' of black iron and a 1/2 breaker bar. We were hired to replace ALL the hardware they torqued.

Point taken from both of you.

I will amend my post to say:

If the hardware was torqued to electrical equipment specifications the hardware will not have reached it's yield strength and can be safely reused.

But if we assume the rules will always be broken we should shutdown all sources of electricity. :roll:

 

[brian john]

Point taken from both of you.

But if we assume the rules will always be broken we should shutdown all sources of electricity. :roll:

Bob I agree with your statement, and this was one job in 39 years in the trade and if we assume all ECs break the rules then all work should be subbed out to me.

 

[iwire]

if we assume all ECs break the rules then all work should be subbed out to me.

Thanks, I nearly choked to death on my coffee. :grin:


No offense to you Brian but the reality is if you really had to compete for with all ECs for the majority of the work out there you would likely go hungry.

The 'system' is set up to promote shortcuts.

 

[cschmid]

Point taken from both of you.

I will amend my post to say:

If the hardware was torqued to electrical equipment specifications the hardware will not have reached it's yield strength and can be safely reused.

But if we assume the rules will always be broken we should shutdown all sources of electricity. :roll:

Come on I bet very few people carry a torque wrench with them..

now this leads to a very interesting topic here and that is bolt and thread torque characteristics. now if you apply the rated torque of a grade 5 bolt to a grade 2 bolt you will stretch the treads, now you torque a grade 2 bolt into a grade ten thread set to a grade 10 torque you now have a bad bolt connection with distorted threads and a few years later you have problem. heat causes faster failure to bolt torques due to already damaged threads..

just something to think about when you loose a bolt and grab one out of the catch all box to save a trip to the hardware store..

 

[iwire]

Come on I bet very few people carry a torque wrench with them.

They should, I have at least two in the truck.

now this leads to a very interesting topic here and that is bolt and thread torque characteristics. now if you apply the rated torque of a grade 5 bolt to a grade 2 bolt you will stretch the treads, now you torque a grade 2 bolt into a grade ten thread set to a grade 10 torque you now have a bad bolt connection with distorted threads and a few years later you have problem. heat causes faster failure to bolt torques due to already damaged threads..

I agree however look at the torque specifications for electrical equipment and you will find for any particular bolt diameter and thread pitch the torque spec is much lower then what the bolt is designed for.

Lets say you are making an electrical connection with a grade 5 3/8" course thread bolt. The equipment manufacturer might say torque to 30 ft lbs but if you looked up the specs for the bolt it might be closer to 60 ft lbs.

just something to think about when you loose a bolt and grab one out of the catch all box to save a trip to the hardware store..

I am very well versed in hardware, I spent five years doing mechanical work on equipment that had to be safe to the public and stand up to close inspection from insurance carriers.

 

[cschmid]

Bob

I do not doubt your ability or knowledge but you are among a small percent of the electrical worker population. A lot of younger apprentices without the experience or schooling in such areas would not know..some of the speed monkeys do but do not care they are getting the job done period. nothing against them but it is the nature of the business.

 

[ohmhead]

Well ive got a question why thur the years when we go back lets just say 1 year or two years to disconnect the temp power gear and transformers and we untighten the bolts to take out temp equipment .

Why does the stainless steel bolts break or snap clean off not all but a few and the grade 5 case hard dont ?


I would think stainless was stronger then the case hard bolts ?

 

[brian john]

I carry a 1/4", 3/8" and 1/2" all my trucks have at a minimum a 1/4" and a 3/8". they are SUPPOSE to use. I also purchased torque screw drivers but have serious doubts about their regular use.

The generator mechanics have a 3/4" Snap-On I am afraid to ask what that cost.

 

[iwire]

Why does the stainless steel bolts break or snap clean off not all but a few and the grade 5 case hard dont ?

Stainless can be pretty strong but it has the downfall of 'thread galling'.



http://www.estainlesssteel.com/gallingofstainless.html

 

[brian john]

Bob

A lot of younger apprentices without the experience or schooling in such areas would not know..some of the speed monkeys do but do not care they are getting the job done period. nothing against them but it is the nature of the business.

Yep!....................

 

[ohmhead]

Stainless can be pretty strong but it has the downfall of 'thread galling'.



http://www.estainlesssteel.com/gallingofstainless.html

Well this has been a problem for years never knew why good page i see now why and i didnt know that stainless will actually get tighter over time due to galling .

I guess stainless for electrical work is not a good connection ?

Now iam wondering what the temp rating of a bolt is case hard at 75 deg or stainless steel at 75 degs which is better or acceptable ?


Meaning would the bolt make a differance per our code ?