Help please!!

[SparkyAndGeorge]

Hi guys, I would very much appreciate some advice here!! Basically was called to a school, every time they clicked the light switch, the RCD in the CU tripped. Meggered the circuit L to E over 299 ohms, E to N, over 299 ohms, but L to N 0.01 ohms. This is correct on a lighting circuit with fluorescent fittings. R1, R2 values all good. This leads me to the conclusion that one of the flo. fittings has become faulty (possibly a small amount of current leaking through to the cpc inside the fitting? But if that was the case, wouldnt that show up on the megger test? When i disconnected the cpc from the CU on that circuit, the lights stayed on! How is the best way to discover the faulty fitting? A lot of head scratching going on today!!!! Any help greatly appreciated, thank you guys.

 

[telectrix]

reason i asked the number is that there may not be a fault as such. florries are notorious for having a bit of leakage. 8 lights can be OK but add 2 more and the cumulative might just push the RCD over it's threshold, esp. if it's a bit sensiitve, like about 22mA.

 

[SparkyAndGeorge]

Flor's are the old choke type. I will ask the client tomorrow if the janitor took any down during the school recess. Thank you telectrix for that answer. I knew they were bad for earth leakage, didnt realise that as low as 8 could trip the RCD.