6A MCB Tripping on Earth Fault Loop Impedance Test

[LewisM]

Hi, just finished a partial rewire at my sisters house and when testing the two lighting circuits (up&down) the 6AMCB trips for both circuits individually, I thought the MCBs might just be sensitive to the test but the smoke alarm circuit also 6A is fine when testing, R1+R2 and IR test all fine just the Loop test causing issues, any ideas??

Thanks Lewis

 

[Risteard]

Because you're injecting a 25A test current into them. It's a known phenomenon which can occasionally occur with B6 circuit breakers.

What did you do to remove the need for RCD protection on these circuits?

 

[buzzlightyear]

try three probes on tester , line ,neural, and cpc. not two.
what tester are you using .

 

[Strima]

Or just add your R1+R2 to your measured Ze.

 

[LewisM]

Answer to all three above, the circuits have rcd protection, was a three prob test, megger 1552 tester and that is what I did in the end add r1+r2 to Ze just the fact it tripped two off the 6a mcbs and not all three is what threw me off.

 

[Deleted member 72666]

Sounds odd to me!

 

[Wilko]

Hi - Do I understand correctly (?) you are trying to measure Zs on a circuit using the low current test (due to RCD presence) and the OCPD trips.