effing dangerous light switch or am I dumb?

[opps]

If you remove the lamp, I bet the LED will go off

If I remove all four bulbs the LED does indeed go out.

I found an old analogue multi-meter (with a low battery). With the bulbs out, and the LED off, I put the black probe on the switched live side of the light switch. With the red probe not touching anything, it read 20v.

When the red probe was attached to the live side, the reading dropped to zero.

Does this indicate that the shock that I got was down to induction and was only 20v? I guess that if the switch were pumping 20v through the circuit the multi-meter wouldn't have dropped to zero when both probes are used.

As I mentioned in an earlier post the effect seemed to be localised in my hand and arm and no further. TBH I didn't think that 20v on a lighting circuit would have been noticeable. Am starting to feel like a bit of a wimp now for complaining about the shock ''

If all of the above is indeed down to induction and not the fault of the switch, short of a full rewire is there anything that I can do?

 

[opps]

If you'd properly safely isolated you'd be fine.

Let this be your lesson, and work safely in future. You might not be so lucky next time.

I fully accept that I was being foolish and lazy.

Further to my last post, in the event of induction however what does one do, turn off the whole consumer unit?

I have often worked on circuits with the MCB turned off and noticed that my electrical screw driver has indicated a very low current (ie. it glows very dimly). In such cases I have put it down to induction, flicked the cables with my finger very quickly and carried on (akin to looking for gas leaks with a lighter I guess).

Do you pros really use a multi-meter every time to ascertain the level of induced current before proceeding?

(BTW the above is a serious question and not intended to should snarky or a defence of my stupidity)

 

[AdrianUK]

Its not down to induction ... its perfectly 'normal' & expected.

The dimmer will use a thyristor to control the load. A thyristor is a kind of electronic switch using a semi conductor device. A semi-conductor switch is only capable of stopping a current flow (and not a potential difference - a voltage). So when the load is removed the semiconductor can no-longer stop the current flow because there is no path so a voltage will appear across the open point - ie the lamp socket.

The regs specifically prohibit the use of semi-conductor switches as isolation devices for this very reason (but in this application it not being used as an isolation device - its being used as a functional switching device so its use is OK).

There is nothing wrong with the device or the wiring - what you discovered is entirely predictable & why you should always isolate at the mains and never trust any form of electronic switching device to give isolation - it wont, it can't!

 

[bernardgreen]

The intensity or pain of a shock depends on the current flowing into the body. Birds perch on 11,000 volt power lines without any shock as no current flows through the bird.


The amount of currrent in the body depends on the resistance ( impedance ) of the entire circuit and the voltage. The resistance of the body and the resistance of the source of the voltage.

In the OFF state the dimmer /electronic switch is high impedance so only a small amount of current can flow but still enough for most people to sense it as only a tingle.

 

[Lectrician]

If you remove the lamp, I bet the LED will go off

If I remove all four bulbs the LED does indeed go out.

I found an old analogue multi-meter (with a low battery). With the bulbs out, and the LED off, I put the black probe on the switched live side of the light switch. With the red probe not touching anything, it read 20v.

When the red probe was attached to the live side, the reading dropped to zero.

Does this indicate that the shock that I got was down to induction and was only 20v? I guess that if the switch were pumping 20v through the circuit the multi-meter wouldn't have dropped to zero when both probes are used.

As I mentioned in an earlier post the effect seemed to be localised in my hand and arm and no further. TBH I didn't think that 20v on a lighting circuit would have been noticeable. Am starting to feel like a bit of a wimp now for complaining about the shock ''

If all of the above is indeed down to induction and not the fault of the switch, short of a full rewire is there anything that I can do?

Put your meter on the LIVE and NEUTRAL or LIVE and EARTH, the voltage will be close to 230v I expect.

 

[AdrianUK]

In the OFF state the dimmer /electronic switch is high impedance so only a small amount of current can flow but still enough for most people to sense it as only a tingle. [/b]

True. But don't forget the snubber network which is probably across the thyristor. This is likely to pass several mA and is liley the cause of most of the leakage current. All fine & dandy when a filament lamp is in the holder.....

 

[RF Lighting]

Further to my last post, in the event of induction however what does one do, turn off the whole consumer unit?

If that's going to ensure you work safely and don't get killed by electrocution, then I'd say that sounds like a pretty good idea.

I have often worked on circuits with the MCB turned off and noticed that my electrical screw driver has indicated a very low current (ie. it glows very dimly). In such cases I have put it down to induction, flicked the cables with my finger very quickly and carried on (akin to looking for gas leaks with a lighter I guess).

Well then you've been very lucky not to kill your self

Do you pros really use a multi-meter every time to ascertain the level of induced current before proceeding?

YES!!! As we understand the dangers of what we are working with and how important it is to prove for dead before we start work.