Contact Resistance

How far away from zero Ω was the busbar resistance, and over how long a piece?

Like discussion before : I have measured the resistance in busbar.

I am assuming you are using a current injection method and measuring the corresponding millivolt drop to calculate resistance.

Can we use contact resistance measurement for motor ?

Are you talking about measuring the winding resistance of a motor?

The following CR4 thread may be of help.

http://cr4.globalspec.com/thread/50934/Busbar-mV-Drop-Test

You are right, my senior tried to use micro ohmmeter. It is correct action?

It depends on the test meter and procedure you are using. Problems with natural surface corrosion on the bus bar (and joint) surface can cause large measurement errors.

I would strongly suggest the current injection method if measuring bus bar or bolted (or similar) joint resistance, this is what our IEC and AS/NZS standards indicate when measuring joint or cable resistance and what we use in our test lab.

You did not answer my previous question, are you measuring a motor winding or are you just measuring the resistance of a bolted (or similar) joint connected to a motor winding?

Measuring micro or Millie ohms is a good idea to ensure proper contacts. One way is by pumping few hundred amps and measuring Millie volt drop across a contact. No spec required. Just compare Millie volt drop across similar joints and ensure that the difference is within 10%. Meters are available to check contact resistance by high current pumping method.