NHP Mod 6 RCD's

NHP is a large distributor in Australia, not a breaker mfr. The breakers that they sell with their own name on them are actually made by Teresaki of Japan. I have never been impressed with the quality of Teresaki breakers of any sort, I can only imagine that their line is MCBs are among the lowest of low.

Being that NHP branded breakers are not sold outside of Australia and New Zealand, I can imagine it likely that the control equipment was made there, despite Astec being an "American mob".

Many MCB units are designed and warranted to interrupt a fault at maximum current rating one (1) time.

Not knowing what type of test you are performing nor the breaker interruption rating nor the current level used for testing it is possible that your test voltage and/or test current level is too high.

Acceptance testing should only be performed once during the life of the MCB at installation and all tests after initial should at reduced test values as per OEM guidelines.

In my opinion replacing the NHP breakers with Siemens equipment is definitely a step in the right direction.

All MCBs and RCDs sold in Australia and NZ are subject to type approval, which helps ensure that they are at least up to the standards that are in place.

This may not necessarily apply to units supplied via a US supply chain.

If you want to get to the heart of the problem, you need to test the RCDs with a proper RCD tester that measures both trip times and trip currents.

Never seen that many all go bad at one time, a very short time, either.

I have to contend with cheap Chinese knock offs here and they are more reliable than that.

Surely a warranty claim is in order.