flickering light / voltstick question

[Stephen]

Hello,

A few weeks ago, I posted about a CFL that flickered in the bathroom. I never got around to posting the conclusion to this.

I found that the neutral had fallen out of the fan isolator switch! As there was no neutral "getting to" the fan, the fan was not running. The permanent and switched lives were still connected to the fan and obviously the other end of the switched live was connected to the light. So I assume that some current was "leaking" from the permanent live through the fan timer circuitry and "going along" the switched live to make the light flicker.

Is that about right? Can anyone give a more technical explanation?

The neutral wire was just hanging in the back box. It wasn't touching the back box. I was wondering if it had touched the back box would that have achieved anything? If there was an RCD or RCBO, would that have tripped? I'm thinking not because there wasn't any current passing.

I haven't got a volt stick. That would have been useful to test if a live supply was reaching the fan or the light but how would you test whether something had a neutral connection? How could I have diagnosed this without seeing the wire physically hanging?

Thanks, Stephen.

[Harry Bloomfield]

Stephen brought next idea :

If an appliance is turned on, with a live supply going to it, the neutral would show on the voltstick as being live. On a T&E, both edges of the cable would show as live, on a flex, you would get a similar effect. Sometimes it is useful to screen the tip of the voltstick probe with a finger either side, to concentrate the detection over a narrower area.

[Stephen]

Thanks but what I was trying to ask is that if the live wire had fallen out, a volt stick would show there was no voltage at the fan. When the neutral fell off, a volt stick would have shown the fan was live. I suppose what I was trying to say is is there a method to detect whether there is a neutral present.

[ARW]

It could be that. Or it could be capacitive build up on the switched live that does not happen when the neutral is connected

It would trip an RCD as the other lights on the circuit would pass some current through this alternative path

Combi check/multimeter?