Required contact area for electrical connection

[beretta24]

Looking for some sparky knowledge here. I'm designing some test equipment and need to make sure I have enough contact area to prevent heating a threaded connection beyond the point where it can be reused.

We will be running 1000V and 1000A through the connection. The real trick is the duration will only be for a few seconds. Should be around 3s but I would like to design for 6s just in case.

Anyone have any thoughts or good reference material? Keep in mind that I am a lowly ME starting out haven't expanded my electrical kowledge much yet. Also, is there a particular contact pressure I need to maintain? Thanks.

Brian

 

[ScottyUK]

Normally you would avoid intentionally using a stud or bolt as a current-carrying component but would use a number of bolts (etc) to provide clamping force over a larger overlapping formed by two or more conductors in the shape of flat bar.

Assuming that isn't applicable to your situation we need to know more about the design of the joint or coupling and the materials it is constructed from.

Some welding connectors use a twist-lock arrangement: the larger ones would probably withstand 1000A for 6 seconds. A word of warning: welder suppliers are very optimistic with their ratings.


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Sometimes I only open my mouth to swap feet...

 

[beretta24]

For the sake of keeping it simple, view the connection as a copper bolt going into a nut. The only real difference is the head height of the bolt is large compared to the threaded portion of the bolt's shank. I also enlarged what would be the face of the bolt head to increase the contact area between the 'bolt' and 'nut'.

The copper of choice for this application is UNS c10200 H04. Based on the info I pulled off of copper.org the minimum yield strength of the material is 40-50ksi depending on the size rod used.

 

[waross]

Let us know how it works out.
respectfully

 

[ScottyUK]

The Copper Development Association publishes just about everything you'd ever want to know about copper. Copper bolts and nuts sounds a bad idea - the material is just too ductile for even a medium torque application. High current contacts use large areas with a jointing paste between surfaces. Have a trawl through this website:

http://www.copper.org

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Sometimes I only open my mouth to swap feet...

 

[Comcokid]

One question. What is the frequency of the voltage? DC? 10kHz? 100 kHz?

 

[waross]

Cadmium-bronze may serve better than copper. It has much better mechanical properties.
respectfully

 

[Warpspeed]

The guiding principle here is to have the incoming wire correctly terminated on a copper lug with a suitably sized clamping hole. These lugs are always made with enough copper cross sectional area applicable to the cable entry size. So engineering that part of it should not offer any difficulty.

This will be held in compression either against another similar lug, or perhaps a copper busbar, brass block, or something similar.

Through this goes a bolt, stud or whatever. The most important feature of this is that the threaded fastner only supplies the clamping force to press and hold the actual copper current carrying parts of the system together.

The bolt absolutely MUST NOT CARRY ANY CURRENT ITSELF. It is only there to clamp and hold the current carrying parts together. If a lot of force is required, high tensile fine threaded steel bolts will be best, used with thick steel washers if necessary. The copper lug must be squashed flat and held rigid against whatever the current has to flow into.

The practiced eye of a mechanical engineer should be quite sufficient for sizing these clamping bolts. If it looks about right and in proportion, it probably is right.

 

[beretta24]

Thanks for the input, in the end we're buying a couple pieces to run through our tensilse tester to ensure the preload will be greater than the centrifugal load (i.e. we maintain contact pressure between the faces of the lead and conductor. Hopefully we can also get some elctrical testing done.

I will try to post results when I get them. What I did to minimize risk in our testing application is to maximize contact area to reduce the current density in the connection. Based on the available contact area, the current density should be less than a third of what it is elsewhere in the DC path.

Brian