mains test screwdriver!!

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I am simply interested in electrics but at a real beginners level.

Could anyone tell me the following please:

Why does a mains test screwdriver only light up when you touch the live/line/phase cable in a socket or light? Every book tells me the neutral cable is always live too, so why doesn't the screwdriver light up when you touch this one?

Thanks..
 
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The reason is the Line/Phase conductor is at 230v AC with respect to earth, when you touch it with the screwdriver (cough splutter) you complete the circuit and current flows through the neon, resistor, you and then to earth, back up some bonding (or rod or similar) somewhere and back to neutral.
The neutral is at about 0v to earth hence it doesn't light, a neutral is classed as a live conductor as it is a current carrying conductor.
Now please put the neon screwdriver in the bin as using yourself as a current path is a bad idea ;)
 
Neutral is classed as a "live" conductor, but its voltage with respect to earth is about 0v.

Line is about 230V RMS to earth, which is why when you touch the screwdriver to it, and complete the circuit with your body, current flows through the screwdriver and through your body to earth.

They are not good devices - as you are starting out don't develop bad habits, throw the thing away and get a proper 2-lead voltage indicator.

This looks ideal for a household starter set - multimeter, voltage indicator and dedicated continuity tester, all in a handy case:

http://www.amprobe.eu/de_DE/showproduct/115/Junior-Set/

PDF brochure: http://www.amprobe.eu/de_DE/downloadfile/115/beschreibung_1/

All in German, unfortunately, as is the blurb on each product:

Multimeter: http://www.amprobe.eu/de_DE/showproductdata/487/Hexagon_55/

Voltage indicator: http://www.amprobe.eu/de_DE/showproduct/116/2000_α_(alpha)/

Continuity tester: http://www.amprobe.eu/de_DE/showproduct/481/TESTFIX/

but it is sold in the UK - the company is now owned by Fluke, and I guess they haven't got all the websites sorted out yet - contact them

(http://www.fluke.co.uk) for info on where to buy.

Right now the English specs are still lurking on the Internet Time Machine from when Beha was an independent company:

http://web.archive.org/web/20060920022629/http://www.beha.com/files_uk/multimeter/93549.pdf


Also see another discussion here: //www.diynot.com/forums/viewtopic.php?t=26282
 
Your body is a large item and is capacitively and inductively linked to earth. So it will allow a small current to flow through the limiting resistor and neon from the line supply to your body to earth thus completing the circuit.

The neutral is already at earth potential so no current will flow.

However the currents involved are so small that it can produce some odd effects and can't be trusted. So the neon screwdriver is only an indication. Using one after already isolating and proving dead can save one when something unexpected happens during the work. For example a borrowed neutral but it should not be used to prove dead.
 
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If you were at the same potential as the line conductor, then it would light the screwdriver when you touch it onto the neutral.
 
They are not good devices - as you are starting out don't develop bad habits, throw the thing away and get a proper 2-lead voltage indicator.

This looks ideal for a household starter set - multimeter, voltage indicator and dedicated continuity tester, all in a handy case:
Don't throw it away it can help where mistakes have been made but do not use the prove dead.

I always recommended to prove dead a device which one can't switch to wrong range and does not rely on batteries.

However we must realise that people are unlikely to buy one think to prove dead and another to take essential measurements with. So where one has a meter there is always the chance you make a mistake. You should use a proving unit but we live in the real world and we know DIY guys are hardly likely to buy proving units so I would keep the neon screwdriver but only as a back-up for when you make a mistake never use it to test with.
 
Heck no, do not throw it away.

Its still a screwdriver after all, just remove the neon inside.
 
I was in my local Homebase the other day and they still sell them.

Are they not illegal in the workplace? Or did I see things?
 
I believe that DIYers sometimes shop in Homebase, and for them workplace regulations do not apply. ;)
 
Oi sunshine, less of the DIYer insinuations ;)

Actually picked up a nice kitchen dining table and chairs in a sale there.
Nothing special but the old one was a bit tatty. And I needed one that expands.
 
Oi sunshine, less of the DIYer insinuations ;)
Well - you take this up with Eric
However we must realise that people are unlikely to buy one think to prove dead and another to take essential measurements with. So where one has a meter there is always the chance you make a mistake. You should use a proving unit but we live in the real world and we know DIY guys are hardly likely to buy proving units so I would keep the neon screwdriver but only as a back-up for when you make a mistake never use it to test with.
while I go and photograph my Martindale test lamp and proving unit... :mrgreen:
 
Now Now, I have a two probe tester and a Martindale and a meter.
No proving unit though, I lick the terminals for that :mrgreen:

But I would not trust a neon as far as I could throw it.
 
Just looking in the equipment case now...

Unitest Multifunction...

Some Korean made clamp meter...

Martindale voltage indicator...

Fluke T5-1000...

Steinel Combi Check...

Some no-identified-maker RS branded 2-pole tester with a LED stack like the Steinel...

Proving unit...


Serious comment re neons for anyone reading this.


It's neon screwdrivers which are to be eschewed, not generally anything with neons in.

This uses neons, but it's very good:

1864martindalevi13700gv.jpg
 

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