Contact Resistance-2500A Busbar Joints

depends on size of bar, size of overlap.

What was specified in purchase orders?

The contact resistance should be less than the equivalent length of the overlap of the joint times its cross sectional area of a single section of the buss bar.

As low as possible, unmeasurable!

It all depends on the cable size and the expected current flow on that cable being joined to the Busbar.

The Heat disspated is = R x I² don't forget. And this is going to happen on the joint surface. for example, a resistance of 0.1Ω on a cable flowing 100A will dissipate 1000W and that is a lot! While the main input cable bringing 2500A, will need to have a resistance of 0.16 mΩ to dissipate the same 1000W

We are talking about very small resistances to achieve negligeable heat dissipation at the joints and concentrate more on the heat dissipation of the Busbar itself when distributing the 2500A. This will be a really hefty busbar. Therefore, look for the Norms about the busbar sizes and designs rather than the joint resistance which should be so low as not to be measurable by normal handy devices. Any resistance in the range of milliOhms is not acceptable on busbar joints.

GA!

Dear AP,

Answer: NIL. Any measureable resistance will give rise to a heating effect which over time will encourage oxidation and therefore a deterioration in conductivity and so on ad infinitum until the joint fails through a 'burn out'.

The clamping with fish plates etc should be at least as long as the bus bar is wide. When fully tightened there will be no discernible difference in the resistance of the joint or a length of the bars.

If you wished to test the veracity of such a joint you would apply a very heavy current (from a test source) at a small PD and measure any temperature rise, or voltage differential across the mechanical joint.

This is a test that is rarely if ever called for these days but was used in the time of 100V DC power systems on marine installations when currents of 1000Amps or more were being carried on the main bars.

Good luck,

Massey.

Ga!

Mmm. I've thought of doing this when commissioning new rectifiers (3kV, 2kA). Getting one of the young engineers to check it out, gut feel is that you're looking at micro-ohms, not millliohms.

There is no universal standard. The busbar manufacturer should specify the acceptable value. If the manufacturer is not available, a typical specification for large bolted connections is 10 micro-ohms as measured by a low-resistance ohmmeter.