electtic shock - RCB did not trip

hardpressed

The moral of this story is never, ever leave a lamp without a light bulb. It's just an accident waiting to happen.

vaio

Nah, the moral is don't stick your fingers into empty bulb holders, especially if they are on

aboard_epsilon

keystone wrote: »

In the limit you are absolutely correct, of course, which is why:

1. With older non-double insulated metal light fittings a tingling sensation can sometimes be felt when touching it and;

2. Even with an MCB in the off position (MCBs being usually single pole) the circuit it protects is never truly dead and your meter can register a very small current t'wixt neutral and earth.

However, IIRC the pd between neutral and earth needs to be of the order of 50 volts to generate the 34mA current sufficient to trip an RCD so a very small pd of the order of 1 or 2 volts will not cause the RCD to trip.

Cheers

when ever i put neutral to earth .My rcd trips
SO either DVardysShadow is right or my system has something wrong.

all the best.markj

keystone

aboard_epsilon wrote: »

when ever i put neutral to earth .My rcd trips
SO either DVardysShadow is right or my system has something wrong.

all the best.markj

No you cannot draw that conclusion from the post you quoted - read it again.

Cheers

vaio

keystone wrote: »

In the limit you are absolutely correct, of course, which is why:

1. With older non-double insulated metal light fittings a tingling sensation can sometimes be felt when touching it and;

2. Even with an MCB in the off position (MCBs being usually single pole) the circuit it protects is never truly dead and your meter can register a very small current t'wixt neutral and earth.

However, IIRC the pd between neutral and earth needs to be of the order of 50 volts to generate the 34mA current sufficient to trip an RCD so a very small pd of the order of 1 or 2 volts will not cause the RCD to trip.

Cheers

Nah, the 50V figure is the voltage general held to be sufficient to cause a noticeable shock to a human. Ie Enough to drive current through the impedance of a human body. (couple of thousand ohms)

RCD’s trip with shorted N-E with only a volt or two on the N because the impedance is much lower

missile

Change out that nurse (and the bulb) for a newer, younger, more energy efficient model.

27col

Or you could buy one of those IKEA/ Wilkinson's/BHS bedside lamps that you just tap with your fingers to make them come on or off. No need then to put your fingers anywhere near the lamp holder.

DVardysShadow

keystone wrote: »

However, IIRC the pd between neutral and earth needs to be of the order of 50 volts to generate the 34mA current sufficient to trip an RCD so a very small pd of the order of 1 or 2 volts will not cause the RCD to trip.

1 volt will give 34mA with a neutral earth loop impedance of 294 Ohms. For 50V, the neutral earth loop impedance would be 14705 Ohms. If the value were above 10 Ohms, that would be an rather poor neutral earth loop impedance. A fraction of a voltbetween neitral and earth will be sufficient to trip an RCD

vaio wrote: »

Nah, the 50V figure is the voltage general held to be sufficient to cause a noticeable shock to a human. Ie Enough to drive current through the impedance of a human body. (couple of thousand ohms)

RCD’s trip with shorted N-E with only a volt or two on the N because the impedance is much lower

I agree with this. Perhaps there is some confusion withe the old style Voltage Operated Earth Trip switch? These were designed to ensure that the potential of bonded metal did not rise more than 40V above earth potential IIRC. These were designed to be used in situations with horrendously high earth loop impedances.

keystone

vaio wrote: »

Nah, the 50V figure is the voltage general held to be sufficient to cause a noticeable shock to a human. Ie Enough to drive current through the impedance of a human body. (couple of thousand ohms)

Ta. I obviously didn't recollect correctly. Must be getting old.

Cheers

keystone

DVardysShadow wrote: »

Perhaps there is some confusion withe the old style Voltage Operated Earth Trip switch?

Yes you could well be onto something there - I was dragging stuff out of the memory banks after all.

Cheers