Mk 7860 uplift

[dokkan1080]

How can I get a 3 wire no trip test of between 2ohms and 1114 ohms

But on a high current test get 0.19 between live and earth and 0.1 between live and neutral.

When the rcd is bridged out I can do the 3 wire test and get a sensible zs of 0.2 ohms.

The strangest part is the first 2 sockets on the circuit can be tested with the rcd in and they still give sensible zs readings....?

 

[SparkyChick]

This is why it's always preferable to do a 2 wire high current test. I believe the 3 wire tests either uses a very low current so as not to trip the RCD or they do some fancy jiggery pokery to saturate the sense coil in the RCD to prevent it detecting the imbalance the test creates (and thus the RCD won't trip).

But... all of this means the reading is much less reliable than the 2 lead high current version. The fact it's so variable should also give you cause for concern and an indication of it's unreliable nature.

Different RCDs seem to have different effects and I have had issues testing through older MK RCDs myself.

Just remember if the readings are garbage you could take an R1+R2 measurement for the circuit, get the Ze for the board and use a calculated Zs (this is a perfectly acceptable means of verifying you meet the maximum Zs requirements).

Regarding the strangest part... have you tested every socket outlet with the RCD jumpered out? If not, I would probably do so as based on the strangest part it could be a bad connection. An R1+R2 test may find such a situation.