Need some ideas - RCD tripping but everything tests fine....

[weevilward]

Hi all,
Customer reports sporadic nuisance tripping of RCD. I cannot reproduce it, or fault anything, except SOMETIMES on EFLI test it trips the RCD (megger mft 1553 'no trip' test).
I'm out of ideas here, can anyone help? This is what I've got:
- TT installation (small domestic);
- 30mA RCCB main switch incomer (Crabtree starbreaker);
- all circuits IR test 8MOhm to L&N-earth;
- RCD testing off load and on load all fine, ramp test 23mA off load 19mA with everything on.
- Ze about 160 ohms down the rod, drops to 12 ohms with all bonding connected.

 

[weevilward]

Someone was asking me about the model of my clamp meter last week. Below is my reply
=================================
They do not make my clamp meter any more.

The nearest equivalent to mine is the metrel md9272 “Metrel MD9272 AC DC Leakage TRMS Clamp Meter - http://isswww.co.uk/metrel-md9272-ac-dc-leakage-trms-clamp-meter?gclid=Cj0KEQjwg47KBRDk7LSu4LTD8eEBEiQAO4O6r3YH-bGd0Dcc_TU7AGRy_t-V1zjTKssQGjcsBeudrN4aAhcx8P8HAQ” but at £300 it is over £100 more than I paid, and I got the cheapest I could find.

Have a look at megger dcm300e “https://www.test-meter.co.uk/earth-leakage-clamp-meter/megger-dcm300e-earth-leakage-clampmeter-ac/” which is roughly the same price.

The best value at the moment if you want a cheap leakage meter is TM-EL9809 Earth Leakage Clamp Meter “TM-EL9809 High Resolution AC Earth Leakage Clamp Meter - https://www.test-meter.co.uk/earth-leakage-clamp-meter/tm-el9809-earth-leakage-clamp-meter/#product_accordian_product_reviews” which is advertised as a resolution of 0.01mA at a cost of £115 so a good price but I do not know if it is accurate or reliable, although they do offer a calibration certificate so it appears to be accurate.

That is really helpful mate, and hank you for that. Above and beyond! Much appreciated. Have a great weekend.

 

[weevilward]

OK - just for a bit of feedback - I spoke to the lady this week, still no tripping of her RCD. (Think that's 3 weeks now). So I am becoming quietly confident that it was a dodgy RCD, and the new one has solved her problem (despite the 8MOhms IR to earth... and the poorly designed installation with one RCD upfront...)
I've advised her about upgrade to RCBO but she's not interested due to cost!

Thanks again for all your help and suggestions and thoughts, out of this thread has come some enlightenment and spurred me on to buy a leakage clamp meter.

Weevilward