Copper threaded rod shears when appling jam nut? 3

[Superslinky]

I have a mechanical question hopefully someone has some experience with. Basically I have a 1/4" copper threaded rod through a panel with a nut and jam nut on both sides containing the rod. one of nuts on each side is pinned with a 1/16" (approx) roll pin. When tightening the jam nut against the pinned nut we run the risk of shearing the copper bar at the point of where the pin hole is. I thought to offset the pin to as far to one side as possible but because copper is so soft I don't know if that will help. I've also considered using a set screw throught the side of the nut but worry that over time and general maintenance it will damage the copper rod.

So my question is, is there another way to accomplish jamming (pinning, locking, etc) the nut without ruining the integrity of the copper rod?

Thanks to all..

 

[CorBlimeyLimey]

Nylok Nut
Loctite

 

[MadMango]

There's also nylon tipped (and other materials) set screws.

http://www.lexingtonsetscrews.com/nylon_tip_set_screws.html

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of these Forums?

 

[dhengr]

And why, pray-tell, do you need both a jam nut and a roll pin through the main nut and the .25" rod, on both sides of the panel? And, how do you locate the pin holes in the rod to assure main nut tightness to the panel. A sketch and a better explanation might help get you better answers. Otherwise, you might try a belt, suspenders, safety pins, and a rope btwn. the legs and over the shoulders.

 

[MikeHalloran]

Don't forget to peen the exposed ends of the rod.


Mike Halloran
Pembroke Pines, FL, USA

 

[MintJulep]

Is this intended to be some sort of ground stud?

 

[Ron]

It doesn't take much torque to seize a jamb nut. Just don't overtighten it.

 

[Superslinky]

I've already considered a nylock and the suspenders seem to be a good idea but....

Here's a sketch. The assembly inserts into a 1/2" hole in the panel and although my "jam nut" looks crude it gets the point across. Basically I'm looking for something simple that doesn't deviate from this design much. The panel can't be changed in any way.

I realize that procedurally, torquing the jam nut as "could be" specified is the easiest solution but this is being installed in the field by a tech with a wrench.

Thanks again.

 

[hydtools]

Use Loctite 290 after tightening the nut against the insulator. It is low viscosity and will wick into the threads and lock the nut to the copper rod.

Ted

 

[MintJulep]

Do not use Loctite if this is supposed to conduct electricity.

Your current flow path is through the mechanical contact of the threads. If you put Loctite in there you've made a capacitor.

 

[MikeHalloran]

Loctite does not change the nature or resistivity of mechanical contacts within a threaded joint. It fills the interstices that would otherwise allow access of air and corrodents, and thereby actually enhances the long term electrical performance of the joint.



Mike Halloran
Pembroke Pines, FL, USA

 

[zekeman]

Get rid of the jamb nut. It is double redundant, and worse, it puts a pin,shear load on the copper rod and does nothing to assure the clamping force you need.

You could use the same rollpin idea ( similar to using a castellated nut for containment) with a spring lockwasher to the panel to assure a clamp or as others mentioned,nylock

 

[MintJulep]

I hear what your saying Mike, but my gut tells me that having Loctite in there isn't going to do good things electrically. I suppose it depends on the nature of the signal.

At any rate, I was taught that an electrical connection that depends on conduction through the faying surfaces of a thread interface is a poor design practice in the first place.

Better to use the threads as intended - to apply force to a terminal and press it directly against a conductor.

 

[hydtools]

The wicking Loctite fill the spaces where there is no mechanical contact, no electrical contact.

OK,then, solder the one mounting nut to the threaded rod to make the nut an electrically conductive shoulder against which the connection and nut are tightened.

Ted

 

[ScottyUK]

How much current does this feed-through have to carry?


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If we learn from our mistakes I'm getting a great education!

 

[PeteDB]

Look to see if you can use Nordlock® washers instead of jam nuts to prevent the nuts from loosening.

 

[potteryshard]

It would seem that you are principally interested in compression force on the terminal at each end, rather than across the insulator stack end-to-end for over all conductivity. The key point is that the field technician must back up the nut against the insulator with a second wrench when tightening the jam nut against the terminal.

I think I'd put two jam nuts against the insulator rather than weaken the through rod with a pin. Bottom line, however, I'd suggest that the 1/4" copper rod is too small... Even 1/4" steel studs are frequently broken off by field people as these small diameters will not stand up to what 'feels right' for a secure connection. Copper, of course will be even more sensitive.

This seems like one of those human factors engineering challenges; the stud may be mechanically and electrically adequate for the task, but unless you can get the field folk to delicately and with a back-up wrench tighten the terminal, the simplest solution may be to just over-size the hardware.

 

[mcgyvr]

Any reason you don't just use off the shelf stud type junction blocks. similar to this

http://www.alliedelec.com/Images/Pr...ooper-Bussmann_Industrial-Control_7400039.pdf

 

[Superslinky]

ScottyUk, the current is around 10,000V @ 20amps. potteryshard, you hit the nail on the head. This situation is indeed removing the human element. And a double jam nut is probably the way to go. I was really hoping for the end all be all solution but it looks like maybe a tag with a "do not over tighten" note might be the best bet. Thanks to all of you for your input.

mcgyvr, I did take the time to design a very similar setup to the junction block. The trouble is (like anything) the ability to to keep form, fit, function. Althought it might work it won't fit and one that fits won't work.

Thanks again everyone...