Earth Loop / Dimmer

[Wonderwall]

Had a strange one today, would appreciate folks take on it. I'm probably missing something obvious!!
Installing some downlights via metal dimmer switch.
Earth loop impedance was 50 ohms at last light!, at switch it was about 1.5 ohms. Dimmer fully up, voltage at light around 230 . Bypass switch and readings come down to 1.8 ohms.
Why would a dimmer cause this?, anyone else come across this ? Am I being a total idiot ( probably!!, it's been a hard week!)
Thanks in advance for any advice.

 

[telectrix]

dimmer electronics will throw your readings down the pan. need to be bypassed for efli testing and IR tests.

 

[Octopus]

Always test with a standard switch before fitting a dimmer

 

[Wonderwall]

Thanks folks.
My confusion is, if I test without the switch and get 1.8 , but when switch is fitted it's nearer 50, what is the true reading ?
When the switch is fitted , is the true ELI 50 ohms or is that just a misleading result .? I hope I'm making sense here.
Thanks again, much appreciated.

 

[westward10]

Thanks folks.
My confusion is, if I test without the switch and get 1.8 , but when switch is fitted it's nearer 50, what is the true reading ?
When the switch is fitted , is the true ELI 50 ohms or is that just a misleading result .? I hope I'm making sense here.
Thanks again, much appreciated.

Your bog standard dimmer switch only lets current through on part of the cycle, it is effectively chopping it which reduces the RMS current hence it "dims".
Your tester will not cope with this and will either give no reading or a false reading. Under a fault condition the internal triac should fail and allow this fault current to flow and hopefully trip the OCPD. Be careful doing EFLI tests through a dimmer as this can also damage the triac. So your reading of 1.50 is correct.

 

[westward10]

I should say your reading of 1.80 is correct.

 

[telectrix]

easy enough to check. bybass the switch with the circuit de-energised then get a R1+R2 reading.