zs test on lights tripping rcd help

[Kelrich]

morning all
i have a problem with the lights in a house firstly they wouldnt seperate as theres a borrowed neutral on upstairs circuit so had to put them into same mcb now when doing my zs test it keeps tripping the rcd any help please

 

[timbobelfast]

What meter are you using? Does it have D lock or an ELIP setting with RCD function?

 

[Kelrich]

metrel easitest mi3000 has a zs rcd function to avoid tripping but it still trips it was fine on rest of circuits just the lights

 

[acvc]

Could it be something to do with the differing lengths of Line and Neutral - due to borrowed neutral - causing an imbalance greater than 30mA between the two, therefore trippping the RCD. Just a thought ...........

 

[invisable]

It sounds like there is a unbalance somewhere try testing mid circuit (if lights have been 3 plated) with switches turned off just to see if it still trips.
Is there a way you can get into the setting on your test kit and change the UL from 50v to 25v and carry out the test again I had a ethos 7920 which used to have to do this to when i was testing circuits in swimming pools protect by 10mA RCDs on that you pushed a button on start up. If you dont have this option test the RCD at 1/2 * if its ok turn everything off link out the rcd and just energize circuit you want to test. It wont trip then