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Hi All,
I had a nuisance rcd tripping fault at a job , I bought a Megger DCM305E earth leakage clamp, which identified the suspect circuit which I swapped out with an RCBO and problem solved!
Ive come home and checked my L-N incomings just to see and I’m showing a 513MA leakage? My board was tested a few months ago and rcds are good.
Any ideas why this is so high but no tripping.
Cheers Ron.
 

Wilko

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Hi Ron - 2 possibilities occur - the leakage is not 500mA or you’ve got dead RCDs. Is there any possibility you’ve not got the correct conductors in the clamp?
 
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  • #3
Hi Ron - 2 possibilities occur - the leakage is not 500mA or you’ve got dead RCDs. Is there any possibility you’ve not got the correct conductors in the clamp?
Hi, that was my first thought on the reading, but I checked the setting against my neighbors conductors and got 15MA then recheck mine and got the same 510MA apro.
I will ramp the Rcds in the morning but I’m confident they are ok.
I’ve got a P V system so I isolated that in case it was that but no change still high.
 
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  • #6
Tell us about the installation, earthing type, where you’ve measured etc :)
It a TN-S, 25mm/16mm tails, measurement was taken between meter and CU. I also check the main earth conductor which showed 480/500MA.
 

littlespark

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If you are measuring before the CU, any earth leakage is not going to affect an RCD on your board.
Your neighbours house could possibly be off a different phase than yours

Can someone correct me here if I am wrong....
It sounds like there is a slight breakdown of the suppliers earth. Is it an old property?

A photograph is always good
 
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  • #8
If you are measuring before the CU, any earth leakage is not going to affect an RCD on your board.
Your neighbours house could possibly be off a different phase than yours

Can someone correct me here if I am wrong....
It sounds like there is a slight breakdown of the suppliers earth. Is it an old property?

A photograph is always good
Hi yes the original house is 1935, I’ve got no tripping issues and my Ze is 0.31
Checking before the Cu should give me the difference and so the earth leakage I thought, but I’m happy to be corrected.
I understand my rcds are not effected but what should be in the low milliamperes is half an amp.
I will try for a pic tomorrow.
 

Marvo

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It's an odd reading. Did you clamp the incoming live and neutral simultaneously?

Test that there's no inadvertant neutral-earth bond within the premises which would be an accidental TN-C and could create alternative paths for the neutral current on a circuit that's not on an RCD maybe....
 
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  • #10
It's an odd reading. Did you clamp the incoming live and neutral simultaneously?

Test that there's no inadvertant neutral-earth bond within the premises which would be an accidental TN-C and could create alternative paths for the neutral current on a circuit that's not on an RCD maybe....
Hi Yes, in two places that I have access.
I’m going to shut down my boards (I have 2 CUs) tomorrow and bring the circuits on one by one and see if anything stands out.
Do you think if I can’t resolve what’s going on I should contact the DNO?
 

Marvo

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I'm not in the UK and don't know how your DNO's operate but from what you say it sounds like the leakage is occuring within the premises so I'm not sure the DNO will be interested. I would live-test all the circuits in the entire installation (after a risk assessment) with the leakage clamp meter to start with and identify any or all the circuits with high leakage current then localise further. If the high leakage is occuring on an RCD circuit then you've got 2 issues to address, firstly the cause of the leakage and secondly why the RCD isn't clearing the fault within the required disconnect time.
 
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  • #12
I'm not in the UK and don't know how your DNO's operate but from what you say it sounds like the leakage is occuring within the premises so I'm not sure the DNO will be interested. I would live-test all the circuits in the entire installation with the leakage clamp meter to start with and identify any or all the circuits with high leakage current then localise further. If the high leakage is occuring on an RCD circuit then you've got 2 issues to address, firstly the cause of the leakage and secondly why the RCD isn't clearing the fault within the required disconnect time.
I will get to it tomorrow and put an update on here, thanks for all your replies!
 
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