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Posted to uk.d-i-y
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Garden lighting trips RCD
On 23/06/2013 18:47, wrote:
On Sunday, June 23, 2013 12:03:49 PM UTC+1, John Rumm wrote:
or use a flasher in the feed
I am sure you don't mean an old git in a rain coat, so could you elaborate?
 If you pull the fuse or switch the mcb off, and clip a flashing
light bulb across it, you then get a mains feed that goes on and off
frequently. You can thus tell with your ground probe how much
difference the mains feed is making, it just means you can do one
sweep not 2. Its a classic old fashioned way to trace circuits.
I assumed that's what you meant, but
(a) is there any sort of two-terminal 'flashing bulb' available that
will work into the load here - predominantly the cable capacitance in
parallel with a highish resistive leak?
(b) I suspect that the flickering display on a DMM might be difficult to
interpret, especially if other time-varying voltages are present due to
other leakages, PME diverted neutral currents, etc.
I've a better idea now: instead of injecting mains, inject an audio tone
(1 to 2 kHz, say) at as high an amplitude as you can manage. You'd need
an audio sig gen and and a power amplifier with a 100V line o/p, or a
standard amplifier plus a step-up transformer. (Do ensure that the
capacitive load and the low primary DC resistance of any transformer
don't upset the amp!)
You can now use an inherently logarithmic detector to look for the
ground leakage signal, i.e. headphones + brain. The 'cans' would need
to be high impedance (Sennheiser 414's come to mind) or used with a
suitable preamp. High-pass filtering can be used to get rid of all the
50 Hz (and its harmonics) 'noise'.
--
Andy
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