Reusing Bolts for Terminations

[iwire]

Well this has been a problem for years never knew why good page i see now why and i didn't know that stainless will actually get tighter over time due to galling .

It does not gual with time, most likely it was tightened till it gaulled and they figured it was tight. Now you come along and try to back it off and it is seized.

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

In my untrained opinion I would say no, it is not a great choice. I would look to what the manufacturers use. I think they go with silicon bronze hardware for critical applications. However most times I think they just use basic low grade hardware that is substantially over sized for the clamping pressures they are shooting for.

 

[ohmhead]

Well i would also think higher resistance of stainless would mean heat transfer would be a issue maybe on a lug or a buss bar to copper or aluminum as far as the rating of the assembly as one part of the whole ul listed equipment not at that temp it would run cooler as current flow would be limited thur it .

I will not use stainless bolts ever after this post makes ya think what we have done in the past .

 

[qcroanoke]

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

What about lightning protection? We use stainless for all connections.

 

[GeorgeB]

Stainless can be pretty strong but ...

The common 303, 304, and 316 grades (non-magnetic) are not very strong. They do stain less than the 400 series which are magnetic. I'll look for some reasonably complete data if there is an interest. In an earlier job, someone replacing the grade 8 (really SHCS) with what they thought was stronger 304 SS got bit HARD. Machines were bent; luckily, no people were.

 

[Pierre C Belarge]

I cannot speak for and do not presume to, for all areas of the country.
My experience in the field and as an inspector does not provide me with a "warm and fuzzy" feeling in regards to torqueing.

There is a percentage of installers who do torque their terminations. Ask some of them when the last time they had the Torque wrench calibrated...look them in the eye and try not to laugh too hard.

Yet my experience is that proper torqueing still leaves a lot to be desired. And
IMHO, most of the improper tightening is over tightening.

 

[Twoskinsoneman]

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.

Bob this whole thread I have thought that your point about the typical torque required doesn't come close to "normal" torque sounded correct. However when I checked those "normal" torques and thought back to torques I could remember off the top of my head I thought these torques are not that different.

I don't know if you were just throwing out numbers but If Im reading this page right the bolt example you listed WAS actually 30 ft pounds and not closer to 60....

http://www.raskcycle.com/techtip/webdoc14.html

 

[iwire]

Bob this whole thread I have thought that your point about the typical torque required doesn't come close to "normal" torque sounded correct. However when I checked those "normal" torques and thought back to torques I could remember off the top of my head I thought these torques are not that different.

I don't know if you were just throwing out numbers but If Im reading this page right the bolt example you listed WAS actually 30 ft pounds and not closer to 60....

http://www.raskcycle.com/techtip/webdoc14.html

I was pulling numbers out of the air but I stand by what I said even if the actual numbers where off.

This GE document lists the torque spec of a 3/8" x 16 fastener with a tensile strength of 120,000 psi (Grade 5) as 16 ft pounds.

(Page 11)

http://www.geindustrial.com/publibrary/checkout/Installation and Instruction|GEH-5875R5|generic

Your link shows 30 foot lbs for the same size and grade fastener. Almost 50% less torque resulting in a greatly reduced clamping / stretching force on the hardware.

 

[ohmhead]

What about lightning protection? We use stainless for all connections.

Well i agree i see SS bolts used on lightning roof point down connections everyday now please don t think iam a expert i was just talking bolts with the other post .



I think stainless bolts if used correctly would be fine i found some information on what galling of SS to the thread & nut means.

The threads act to weld together by SS metal to SS metal tightening & Heat on SS they brake or snap after years of this problem .



But the good news is if you use a bronze nut on SS bolt it doesnt happen no galling effect .



But i dont know how temp would effect a bolt on SS as to a electrical connection on a buss or lug iam still wondering ?



I think one should use what the factory installs in the equipment but on most power company transformers we have used SS nuts and bolts .

And they brake because we reuse them over and over on each temp service .

 

[Twoskinsoneman]

I was pulling numbers out of the air but I stand by what I said even if the actual numbers where off.

This GE document lists the torque spec of a 3/8" x 16 fastener with a tensile strength of 120,000 psi (Grade 5) as 16 ft pounds.

(Page 11)

http://www.geindustrial.com/publibrary/checkout/Installation and Instruction|GEH-5875R5|generic

Your link shows 30 foot lbs for the same size and grade fastener. Almost 50% less torque resulting in a greatly reduced clamping / stretching force on the hardware.

Ok great example. Amazing how the torques vary. I know I've seen 1/2" bolts calling for 55ft-lbs torques (although I don't have a link) and the GE instructions list their 1/2" torques at 39ft-lbs"

In any case I agree with you that the torques listed for electrical equipment rarely reach standard torque values. So good point.

 

[Besoeker]

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

I agree that the yield point isn't generally exceeded.
For busbar connections we use high tensile bolts and disc spring (Belleville) washers. This allows for thermal expansion and contraction whilst providing good contact pressure.
But, as a rule, we don't reuse them. We may not know how many thermal cycles they have endured, their quality, or how well they were installed and maintained.
For most extension and retrofit installations (for us), replacement represents a very small part of total hardware costs.

 

[Power Tech]

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.

I used to do a tremendous amount of work with batteries. Cleaning, using the washer upside down so the cupped side is toward the terminal. Touring and no-ox is extremely important.

We used the Biddle micro-ohm meter to test the connections. Very accurate, would pick up an additional washer installed.

I am surprised he did not crush the lead terminal.

110 in pounds is good 200 must be better.:roll:

 

[brian john]

I have been installing and servicing batteries for 30 some years. And in that period I have seen some ECs not familiar with installation practices lose lots of money.

 

[Power Tech]

I have been installing and servicing batteries for 30 some years. And in that period I have seen some ECs not familiar with installation practices lose lots of money.

It is definitely a specialty.

Makes me want to get back into it.

 

[daleuger]

I've once or twice had the bolt on a ground clamp snap off with very little effort at all but I think this is likely due to copper being such a soft metal. :roll:

Then again "give er all she's got" isn't always the answer either.