Neon Screwdriver

[Hainsey]

I am relativley new to these boards & to DIY and over the last couple of months I have been reading the top notch advice given by seasoned posters.

One of the things I have noticed is the repeated recommendation to NOT use a neon screwdriver to test a circuit is dead before working on it.

My question is why? I'm not stating that the advice is wrong but simply want to clear up why because over the years I have always used only a neon screwdriver to test dead. What should I use instead? i don't want a belt one day when I could have easily avoided it.

Please advise. Thanks

 

[davy_owen_88]

Neon screwrivers rely on your body providing a path for the current to flow from Phase through the neon and eventually to earth. It limits this current using a resistor but if your resistance to earth is also very high then the neon may not light up, as as soon as the resistor is removed from the circuit your resistance to earth suddenly drops and you are in a potentially lethal situation.

It is also quite hard to see the neon glow in bright light, so it's easy to mistake a positive test for a negative.

Then you have the chance that the resistor will fail due to being damaged.

Add to that the fact that they are crap screwdrivers and it soon becomes appararent that nobody should waste their money on them

The only item recommended for proving dead is an approved test lamp or voltage indicator.

 

[Hainsey]

Neon screwrivers rely on your body providing a path for the current to flow from Phase through the neon and eventually to earth. It limits this current using a resistor but if your resistance to earth is also very high then the neon may not light up, as as soon as the resistor is removed from the circuit your resistance to earth suddenly drops and you are in a potentially lethal situation.

So am I right in thinking that if the resistor in the screwdriver fails then when I'm testing I could get the full current through my body? Think I may be doing some online shopping VERY soon .

Thanks davy_owen.

 

[FingRinal]

As good as the Flukes are, unless you first test Line to Neutral, Line to Earth trips 30mA RCDs...

Must admit, I've not tried it with the breaker off. Need to try it.

Also, whenever I need to be sure 100%, I always reach for the Martindale. Maybe it's just habit but I'd like to think it's confidence.

 

[aptsys]

So am I right in thinking that if the resistor in the screwdriver fails then when I'm testing I could get the full current through my body?

No, the current through a neon will not be enough to do any serious damage.

 

[ban-all-sheds]

Think I may be doing some online shopping VERY soon.

http://cgi.ebay.co.uk/Martindale-VI...260913588QQcmdZViewItem?hash=item290260913588

http://cgi.ebay.co.uk/MARTINDALE-VO...275671670QQcmdZViewItem?hash=item270275671670

http://cgi.ebay.co.uk/MARTINDALE-SA...305581375QQcmdZViewItem?hash=item120305581375

http://cgi.ebay.co.uk/MARTINDALE-VO...291316007QQcmdZViewItem?hash=item230291316007


Plus proving units:

http://cgi.ebay.co.uk/Martindale-Pr...260912454QQcmdZViewItem?hash=item290260912454

http://cgi.ebay.co.uk/MARTINDALE-P-...262920904QQcmdZViewItem?hash=item170262920904

http://cgi.ebay.co.uk/Martindale-PD...267209216QQcmdZViewItem?hash=item140267209216

 

[Kes]

I don't think they should be dismissed out of hand. They are usually robust depite costing peanuts, and give a simple understandable indication of a live current.

What I would like to know (in the same spirit as the OP) is how do you prove that the earth is sound when you use a test lamp or other more sophisticated device? You may not be able to test it using a known live source (too far away) so you could get a false reading.

 

[ban-all-sheds]

Your proving unit tells you that your tester is working.

If the tester lights up between L&N but not L&E.....

 

[GaryMo]

What I would like to know (in the same spirit as the OP) is how do you prove that the earth is sound when you use a test lamp or other more sophisticated device?

Use an Earth Fault Loop Impedance meter.

 

[333rocky333]

Dont forget these ones
http://www.martindale-electric.co.uk/drummond.htm

 

[plugwash]

If the tester lights up between L&N but not L&E.....

What if the tester doesn't light up at all? You think the circuit is dead but you can't really be sure because it could be that live is intact but both neutral and earth are broken.

You could energise then test then deenergise and test again but that isn't always practical (e.g. some part of the circuit may not be in a safe state to energise)

 

[Softus]

If the tester lights up between L&N but not L&E.....

What if the tester doesn't light up at all? You think the circuit is dead but you can't really be sure because it could be that live is intact but both neutral and earth are broken.

You have to use the means of isolation to energise the circuit in order to be sure that that means of isolation can then isolate it.

You could energise then test then deenergise and test again but that isn't always practical (e.g. some part of the circuit may not be in a safe state to energise)

In that case you have to use a wander lead to a known earth in order to prove that the circuit you're working on isn't energised.

Clearly you would test the wander lead before trusting it...

 

[THRIPSTER]

Imagine this - the case of a metal CU is live due to schaffed cables entering a non - grommeted hole. I test with my neon screwdriver and it shows a voltage present. I test with a two leaded tester between the case and what I think is a good earth and it shows nothing because this earth is also (for whatever reason) at mains potential. Given this scenario (or others in the same vein) which method would you advocate to initially ensure your safety? Does the infinitessimally small risk of using the neon screwdriver outweigh the chances of danger which might possibly be encountered in the type of scenario described above - I think so.

 

[BS3036]

I hear a lot of times that neon screwdrivers are dangerous because you have to complete the circuit through your body, and that you should use a 'proper' bit of test gear made by a recognised company.

Untitled

• BS3036
• 18 Sep 2008
• 1

Untitled

• BS3036
• 18 Sep 2008
• 1

What I don't seem to hear mentioned is that such instruments also have a stud which you have to touch, to complete a circuit when doing single ended live tests.

My main concern with neon screwdrivers is that they are often so badly made that you have to hold it at a very particular angle to actually be able to see the glow, leading to false negatives.[/img]

 

[333rocky333]

Them prongs look a bit long though.