Garden lighting trips RCD

[Gefreiter Krueger]

That was the beginning of the end.

[Tim Watts]

On Sunday 23 June 2013 19:43 Gefreiter Krueger wrote in uk.d-i-y:

RCDs for outside leads and lawnmowers, either as fitted plugs or adaptors, have been around since the 70's and have always be most recommended.

To come onto a public group and suggest that RCD protection be removed because it's a bit incovenient, is uttery and grossly irresponsible.

There is a reason the current IEE/IET wiring regulations regulations require it.

Now you are entitled to your opinion, but in these matters it is best not to offer them to an unknown audience who might be foolish enough to follow your advice.

[Andy Wade]

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'.

[meow2222]

You can switch a filament lamp on to give it some load.

I havent seen thermal flashers in decades, you could probably make an equivalent using a relay though, with RC charging.

Sure, you need either audio detection or an analogue meter.

mains transformers are fine at that freq.

At least 5ohms dc for an 8 ohm amp, preferably 8.

A simple opamp can get you a wide range of gain

yes, if needed. Even if 50Hz drove the opamp to clipping it wouldnt stop the tone indication working.

You might just use a self oscillating relay direct on the mains, with a series lamp to limit i and a 2nd parallel lamp to limit V_out to 50v max. A small relay chopping mains at 200Hz or so would get you a very different sound to 50Hz. Hi tech stuff.

NT