Shower - Neon light flickering when switched off at isolator

[DPG]

Hi all.

Upgraded an old Wylex single fusebox for a combined RCD/MCB unit today, also replaced the pull-cord switch as it was approx 15 years old and was getting warm after a few minutes use.

Anyway, all good - shower working, isolator working. Only thing is when they went in the bathroom later with the light off (I know, don't ask!) they said the neon 'power' light on the shower unit itself was lit even though the pull-cord was off. They did say it was definately dimmer than when the pull-cord is switched on.

When I tested it the neon definately went on and off when the isolator was operated, but obviously I didnt check it in the dark.

Now, I reckon this is probably inductive pick-up but would like to hear other people's opinions on this. It may be that it did it before I changed the switch today, but they never noticed it?


Any thoughts?
Cheers, Daz.

 

[DPG]

Just to clarify, in line 3: the neon in the isolator goes on and off when the isolator is operated, but the neon in the shower itself doesn't go fully off when the isolator is off.

DIfficult to get into clear words!

Cheers, Daz.

 

[topquark]

Start with the basics, inspection and then test I assume you've already done that for the circuit up to the shower isolator by virtue of having changed the CU. So test the load side of the isolator and confirm it's completely dead when isolated, they have been known to allow current flow when isolated. Then move on to the shower unit and check that (with the isolator off), the neon won't glow without a PD, so it's there somewhere providing a current

 

[WDMDL]

Possibly a crossed connection in the isolator...eg L-OUT and L-IN crossed. In effect you would get a leakage path between the incoming line and the outgoing neutral, through the isolator's neon and the 270k-Ohm resistor. This would then flow through the "Mains ON" neon and resistor in the shower itself, the stray capacitance between line and earth of the cable between the isolator and shower effectively making up the circuit.

Simon.

 

[DPG]

WDMDL - spot on! Just checked it now and it was crossed wires, how embarassing. Obviously wasn't as careful there as I should have been.

To be fair, the way the cables were formed coming through the ceiling, the live from the incomer looked like it was coming straight from the sheath of the shower cable. I know this doesn't excuse it and I obviously wan't taking enough care on this one.

Daz