Electrical Bonding

[EagleRacer110]

Hey guys,
Im currently working on a project at my internship dealing with electrical bonding. I need to design a model or "device" to test the resistance between to metal connections,but i dont want the connecting hardware (bolts, washers, nuts, etc. to sway the data. Any suggestions on how to design this, or ways to prevent the hardware from tainting the data
Thx in advance

 

[IRstuff]

The resistance test method should be a "Kelvin" probe or measurement (

https://en.wikipedia.org/wiki/Four-terminal_sensing),

which is 4-wire setup that runs current through the outer two connections and measures voltage across the inner two probes. This eliminates the resistance of the probe contacts. As for your hardware, they are often what carries the current, so eliminating them is typically not possible in a production configuration. You would have to put the metal pieces in an insulated vise, apply the correct clamping force and then do the measurement; however, that's meaningless for operational hardware, since it's the nuts and bolts that apply the clamping force, which is difficult to duplicate in a vise.

Note that the bonding resistance is usually on the order of 25 milliohms, so a regular ohmmeter will not properly do the measurement. Also, some bonding resistance meters actually have probes that essentially drill into the metal to make the measurement, since some metals like aluminum have a native oxide layer that's insulative and you can get erroneous resistances without breaking through the oxide to get to the bulk metal underneath.

This is all assuming you are doing an EMI-related bonding measurement, which is different than an electrical power system bonding.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[desertfox]

Hi Eagleracer110

I wouldn’t worry about the hardware affecting resistance readings, provided the bolts are tight and the copper connections are under pressure from the bolts, the electrical current will flow through the least path of resistance ie copper to copper.
See the link below:-

https://electrical-engineering-portal.com/res/Copper-for-busbars.pdf

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein