Live light switch!!

[redconker]

Live light switch!!
Hi there,

when I touch the screws on the wall light switch cover with an electrical testing screwdriver it shows current. I can touch the screws and can't feel a current but am a bit concerned as I imagine this means the earth has a live current.

Is this normal? - I only tested this by chance and haven't tested other houses and if not, can anybody recommend where I should start in identifying the problem (if there is one)?

thanks.

 

[flameport]

The problem is with the 'electrical testing screwdriver '

They are useless devices, and can illuminate for all kinds of reasons.

 

[aptsys]

It does however give a good indication that maybe the earth is not connected or left floating. Worth investigation.

 

[redconker]

It does however give a good indication that maybe the earth is not connected or left floating. Worth investigation.

Okay thanks - I understand that a lighting circuit runs in a loop - are you saying that one of the earths is possibly not connected?

 

[rebuke]

It's possible that you don't have an earth to your lightswitch (not ideal, but as long as you don't have a metal fronted switch not too much of an issue), or that perhaps it has become disconnected somewhere (which would be more worrying). It's also just as possible that your neon screwdriver is being a typical neon screwdriver, and giving you very misleading information...

 

[sm1thson]

If your screwdriver is of the type with an LCD and no battery and the screws are on a plastic faceplate screwed into a plastic backbox then I would agree its an erroneous reading.

if the screws are such that they should be connected to earth (metal faceplate/ backbox), then as stated above it would appear the earth is floating (and a voltage present due to capacitive coupling), if the screw driver is a neon then it is pretty certain your earth isn’t connected (at the other end of the cable to the switch) as the neon would need 80ishV to light, although if you touch it will not feel like 80V as then you change the circuit and drain the capacitive charge away (not enough current to feel it)

The wiring will function with no earth but you have no protection. from a further fault a live to earth fault will make your switch screws deadly (and possibly other metal parts depending on what is present and where the break is).

 

[redconker]

Thank you sm1thson for your comment. The backbox is metal and earthed. Where would I start looking for a loose earth please? I can look through the connections at the consumption box but if it's not there ....?

 

[ericmark]

Go Here and download ESC Best Practice Guide No.1 This will I hope let you understand better the problem.
Although it may be simply one wire not connected it could also be that earths were never connected and I am not sure this is really a DIY job!

 

[Taylortwocities]

And while you are at it..

Untitled

• Taylortwocities
• 11 Feb 2009
• 20

 

[ericmark]

What wrong we neon screw driver when working on a IT supply on a tunnel boring machine they stopped me getting many a shock. Would fill them with re-enterable compound to stop them getting wet and they were cheap enough to replace on regular basis.
In there place they are good tools although I would not use them on items which should be live only on item that should be dead.
If you have ever worked on a IT system in a wet environment you would also I am sure use neon screwdrivers.

 

[bernardgreen]

Stand close to a light switch where the live is looped at the switches and use a neon screwdriver on a water tap and it might glow to "show the tap is live" even though the tap is connected by continuous copper pipe to the main earth bonding.

The neon glows so the tap must be live. ?? No it glows because the capacitive coupling between you and the live wires to the switch raises you body's potential enough to strike the neon. Not enough energy is coupled to be dangerous but enough to give a very mis-leading indication.

If you have ever worked on a IT system in a wet environment you would also I am sure use neon screwdrivers

Radio transmitter sites. Often wet Depending on the power and frequency of the transmitter it is no un-known for a neon to glow when on the desk near the feeder cables.

If you are in a wet area and you get a clear indication from a neon that a piece of metal that should be earthed is live then take great care. The piece of metal may be properly earthed and the wet area is the live area.