Low resistance measuring - High vs. Low current methods 4

[lz5pl]

I have to buy some micro-ohmmeter for field testing of contact resistance of CB's, disconnector switches, busbar joints, etc.
I have a choice between instruments using high DC current and low DC current. Both types have sufficient resolution and accuracy, that with low DC (actually 2A)can be used also for measuring of transformer windings resistance.
Could you advice me whether there are some advantages/disadvantages of both methods, as well as some specific standard requirements? I work in the IEC world, but suggestions based on ANSI requirements are also welcome.

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It may be like this in theory and practice, but in real life it is completely different.
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[lz5pl]

Some more detailed search led me to the following standard requirement:

IEC 60694 Common specifications for high-voltage
switchgear and controlgear standards

6.4 Measurement of the resistance of circuits
6.4.1 Main circuit
........
The current during the test shall have any convenient value between 50 A and the rated normal current.
........

This result doesn't make me happy ...


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It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant

 

[electricpete]

That is similar to the requirement that zogzog cited (even more severe). It puts you in a tough spot.

The paradox - we have to try to read the mind of the standards-writers. Are they requiring 50A because:
1 – Historical. In the old days there was not a reasonable available low current device to make those measurements accurately in the field. So they assume lower current measurement won't be as accurate and specify higher current measurement .(in which case it would have made a lot more sense to just specify an accuracy rather than a test current).
....or...
2 – they know something we don’t?

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[lz5pl]

If I have just to measure these contact resistances I would go to modern low current instrument without problems. It is clear that standard is not updated in line with more modern measuring technology, so I would be confident with 2 A current measurements.
My problem is that I am in procedure for accreditation of Inspectuion Body in the company. These people from accreditation agency are looking only in the papers and will not accept any deviation from the standard even if the instrument injects 49,9 A instead of 50.
They rejected my test forms because resistance units are written as Ohms, instead of the corresponding Greece letter !

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It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant