CB or conductor termination contact resistance

[ron]

Does anyone know a reference that may show generally acceptable resistance for circuit breaker contacts, switch contacts and conductor terminations?

I was guessing at 100 micro-ohms for 4000A LVPCBs but wasn't sure for long barrel compression and mechanical set screw type conductor terminations.

 

[zog]

Does anyone know a reference that may show generally acceptable resistance for circuit breaker contacts, switch contacts and conductor terminations?

I was guessing at 100 micro-ohms for 4000A LVPCBs but wasn't sure for long barrel compression and mechanical set screw type conductor terminations.

Depends on the exact breaker but for a 4000A LVPCB you should see <20 microhms.

 

[brian john]

A one or two hole termination connector 3-8 micro-ohms.

 

[LarryFine]

This sounds like a job for FOP man!

 

[brian john]

This sounds like a job for FOP man!

If the measurements are a requirement of the specifications a Ductor/Micro-ohm/DLRO is a mandatory instrument.

 

[ron]

The reason for the question is due to an underrated piece of switchboard.
It is existing and installed about 5 years ago.
The three phase bolted fault calculated result is below the SWBD AIC/withstand rating. The x/r ratio at the board is >6.6, so with the derating, the board and its cb's are now underrated.
Since the IEEE/ANSI method of calculating fault current is conservative, and ignores small impedances such as contact resistance, I thought if I added them into the model, it would calculate a value below the rating.
Also due to the high x/r value, the L-G calculation is higher than the three phase bolted fault value, so I'm just trying to add real life impedance to ensure the equipment is adequately braced.