RCD not trippng

[nickblake]

RCD tripping problem , i have installed a RCBO on a lighting circuit ,and the RCBO wont trip under test conditions , R1 R2 Reading was 0.58 Zs was 0.74 ,but when i test on 30 ma x 1 @180 degress the tester says its tripped in 30 ms but hasnt physically tripped , ive changed the RCBO and its still the same ,also connected the earth to an earth of another circuit and the RCBO trips ,testing it with the meter across the RCBO at the board it trips in 23 ms , all i can think of that there is an earth fault that is not showing up under normal test conditions but only showing when the RCD test is is carried out as the RCD test is testing the circuit under fault conditins am i correct in assuming there is an earth fault any ideas , meters fine tests Any onther circuit as all 14 are on RCBO's just the one that wont trip

 

[Sparky Ninja]

also connected the earth to an earth of another circuit and the RCBO trips

What do you mean by this?

 

[nickblake]

as it say from the tester to an earth of another circuit

 

[Sparky Ninja]

so do you mean the earth lead of the tester to aseperate RCBO all together? Or are you testing the original RCBO but connecting the earth lead to another circuits CPC?

 

[Deleted member 9648]

Are you testing on the switched side of a dimmer?.....that might cause odd test results.

 

[nickblake]

no my friend just a normal switch MK grid switch its a wiard one i can tell you , every thing tests out fine R1 R2 are ok Zs is OK insulation resistance is over 200 meg , but wont trip the RCD on just this one circuit all the other RCBO's trip fine 24.6 ms to 28 .2 ms , there on lights and sockets , its just this one circuit real head scratcher to me all i can think is when the RCD tester puts the fault on the circuit the cable cant handle the fault current the RCD is not detecting the fault

 

[nickblake]

yes widdler its to the same RCBO but connected the earth to another circuit that just to prove that the RCBO is functioning with another earth

 

[Deleted member 9648]

no my friend just a normal switch MK grid switch its a wiard one i can tell you , every thing tests out fine R1 R2 are ok Zs is OK insulation resistance is over 200 meg , but wont trip the RCD on just this one circuit all the other RCBO's trip fine 24.6 ms to 28 .2 ms , there on lights and sockets , its just this one circuit real head scratcher to me all i can think is when the RCD tester puts the fault on the circuit the cable cant handle the fault current the RCD is not detecting the fault

Mystified then

 

[davelerave]

hard to figure

N-E IR on the circuit is ok?

and the continuity on the cpc is already checked

 

[nickblake]

yep every test was ok NE over 200 Mohms scrattching my head on this one

 

[mogga]

have you tried the obvious Swapout ? possibly faulty rcbo ??

 

[nickblake]

yes that was the first thing i did changed the RCBO ,also swapped the wire to another RCBO and it wont trip , it must be some thing with the earthing to that circuit but it all test out ok R1R2 fine IR all conductors above 200 meg ohm ,Zs fine just wont trip , think ill have to strip the circuit down and do RCD tests at every point on the circuit till i find the point where it stops tripping ,ive tried Zs and RCD at 4 of the 5 points and i doesnt trip its very wiard