RCD trips on 'no trip test'

[the_pasty]

hi,
I'm testng a ring main and on the Zs 'no trip test' using a Megger the RCD keeps tripping. Anybody have any ideas why this could be? R1, Rn and R2 ring continuity all fine and polarity at all all sockets good. Ring is about 85m long.
Thanks

 

[Click-Sure]

Tried testing the RCD or swapping it out any trying again?

 

[securespark]

Tried testing the RCD's as manufacturers intended, ie in isolation?

 

[Spark123]

You got a good neutral connection if required?
New batteries in the tester? What does it go at if you ramp test it?

 

[GaryMo]

You may have no choice but to record a calculated Zs if you prove the RCD is operating fine.
Have you got access to another meter?

 

[DESL]

What were the results of the full range of tests on the RCD as said before in isolation of any ccts.

The Megger puts 15mA to earth on 'no trip' 3 lead test, so if for example if there was around 8mA of earth leakage on the RCD side of the board this would be sufficient to trip RCD

 

[ebee]

Have you removed all circuit loads prior to the test?