Another RCD problem

[jibjob]

Fitted a standalone fused 30mA RCD unit today protecting a spur from existing circuit wired directly from MCB in CU. RCD FCU is mounted adjacent to CU. CU has 100mA RCD upfront (Crabtree) & is populated by 60898 MCBs. 30mA RCD x1 test was fine (28ms) but the x5 test trips 100mA as well as 30mA RCD with a result of 41.80ms. Test is carried out from new socket outlet. Furthermore, if the 100mA RCD trips, upon resetting it the 30mA RCD trips of it's own accord.
Anyone have any ideas as to what might be occuring? Cheers

 

[Mr.Ian]

I'll try it out just to see out of curiosity, but I would've thought unless there was a fault on the load side of the RCD then it wouldn't trip. If it's not supplying anything (no load) the RCD still has 230v on one side and 0v on the other yet it doesn't trip, when there's an inbalance under load it will trip. I still can't see really how the supply could trip it.
I am a bit tired mind you and could be having a senior moment !!!!!!!!!

 

[Spazz]

Im thinking as the jibjob said the supply was knocking the RCD out, but when the MCB is turned off, cutting the power (also the isolator is off) - there must be a earth leakage between the CU and the isolator on the line side.

If this was on the neutral side the RCD will still be tripping out.

The other problem might be an issue with the cpc on the cooker circuit - do a Zs on that as well and a R1 + R2.

What supply do you have? TNC-S??