How Does a neon screwdriver work?

[Paul_C]

We use these when installing meters as they are deemed the only instrument to prove polarity.

So a voltmeter with one side connected to an earth spike driven into the ground wouldn't work then?

 

[ban-all-sheds]

Or a test lamp between the supply earth, if there is one, and the two live conductors in turn?

If one makes it light up, and the other doesn't, is it possible for the one which makes it light up to be neutral, and the one which doesn't to be line?

 

[westie101]

Or a test lamp between the supply earth, if there is one

And on a PME 2 wire supply?

So a voltmeter with one side connected to an earth spike driven into the ground wouldn't work then?

The approved method did used to be that but using a test lamp. However it was pointed out that the earth spike needed to be "guarded" from interference and that in some premises the cable length to outside was excessive.
In this case and this case only a single contact device (volt stick) can be used, but only for a polarity check.

 

[ban-all-sheds]

And on a PME 2 wire supply?

Oh b****cks.

 

[ericmark]

While working on a tunnel boring machine in Hong Kong with a IT system I realised how good the neon screw driver was. I touched it on every bit of metal before touching it with my hand. Saved getting a shock. Real problem was IT system having no neutral (Delta secondary on step down transformer) there was no earth either. Plus loads of water with iron salts in it.

No the neon was not used for electrical testing one had to find two lines as day to day which of the three phases would be down to earth would change. But they did stop one getting a shock.

They are also useful where something un-expected has happened. A contactor or relay closes and makes the cable you have proven dead live. Or a shared neutral means as one disconnects the neutral becomes live. Yes it shouldn't happen but it does. So any extra indication must help.

So never used as a bit of test kit but I do use them so as to get a warning when something becomes live when your working on it. Including another electrician using an insulation tester on the same system as your working on.

To me to prove dead first you must prove where feed from. So if you have something which is live and you switch off an isolator and it's then dead great. But you can use all the testers and proving units you want but if it is then made live by a switch or contactor after been shown to be dead you will still get caught out. In a large factory one has to hope the plans you have are correct and hope it can't be made live. But often one can't trust plans so neon screwdrivers are one way of preventing mistakes from catching one out.

OK in a house you should be able to switch off the main incomer and be safe. But even then I have found a socket connected to next doors supply.

So yes you will find neon screwdrivers in my tool bag.

But with a TN or TT system then to measure voltage to earth may work but not with an IT system. But I want to measure volts no led or neon lights. If I measure 210 volts on a 230 volt system I know there is something wrong. Be it a track formed after a flash over or any other leakage I know something is wrong. Use a neon tester it shows nothing like that. With the old bulb tester with 15W bulb it was easy to show something as dead and still get nasty belt. Maybe not enough to kill you. But the LED and neon work with less current so will show a track.

In the old days switch the meter from 250 volt range to 500 volt range and see different voltage it would show it came from a track. But gone are the days when one lugged around the AVO Mk7 or Mk8.

I have used a clamp on for years. Best tool I ever got. Before I disconnect a wire I test to see if current is being drawn. Specially with neutral wires. How can one ever prove a neutral as dead without a clamp on meter? Yet look around and see how many electricians still don't have one in their tool bag.

Let him without sin cast the first stone. I am living in real world and anything I can do to reduce the risk I will do. Including using where I can neon screwdrivers.

 

[Wontdothatagain]

So a voltmeter with one side connected to an earth spike driven into the ground wouldn't work then?

I am given between 5 and 6 appointments a day. If i was to bang an rod into every job, i would never get home.

If i had to bang the rod in outside of the property, who is going to stand by it and stop the owners dog from cocking his leg and getting a nasty belt from the potential difference that i have created

 

[ericmark]

I think you have hit nail on the head.

We all know what we should do.

We also all know we would never get the work done if we did it all.

So we take a risk assessment and do what to us seems a sensible compromise.

The problem arises when some one who does not know what he should do, copies some one who has done a risk assessment using same methods, but where the risks are not the same. Or has missed some vital stage.

If I give an example watching work on a TN system then copying with a TT or IT system. We walk into a building and glance at the head, we test the ELI and note the reading which confirms what we thought. We just switch off the MCB controlling that circuit and do the work. And although switched off we work as if live just in case we have made an error.

The DIY guy is watching us. He thinks that's easy I can do that myself, but he does not look at the head, and even if he did would not know what he is looking at. Since he did not test the ELI before starting he has no idea if circuit was live to start with, he guesses at which MCB to turn off, and does not have the ELI meter still plugged in, so does not really know if he has guessed correct. And works in a manor that if it is still live he will get a shock.

And then of course he does not test completed work.

OK we should have plugged the ELI meter into a proving unit if using it to show no voltage on circuit. But by both treating as if live and using neon screw driver the chances of getting a shock are very remote. Other than working in petro-chemical where not having proving unit to hand resulted in site pass being withdrawn (Which was same really as sacking one) I have not seen many electricians walking around with a proving unit. Where cables were bolted so I had to put a spanner on the terminal then I took a lot more care in proving dead.

In the end got caught when some one removed my lock. Not really something I could guard against.

 

[david911cockburn]

Firstly,
To the chap with the 'live' cable that wasn't connected at either end; do you trust your wife?

Secondly,
The idea of asking the question "how does a neon screwdriver work", was to assess whether or not everybody was aware that current will pass through the human body and that you can get a 'shock' from a 230v supply.
This may seem silly, but a number of contributors to this and the IET forum claim that this isn't possible!
Using a neon screwdriver is safer than asking you all to touch an energised line circuit conductor, in order just to prove the point.

Having said the above though, what you have all written makes absolutely fascinating reading. Thank you all, I'm very impressed with your knowledge and experience.

 

[sparkticus]

Having said the above though, what you have all written makes absolutely fascinating reading. Thank you all, I'm very impressed with your knowledge and experience.

Are you qualified to make that judgement?

You will find that you will receive much warmer responses if you put some effort into posting clear concise questions or propositions and then follow through with reasonable interactive discussion. Your current approach makes it seem that you think you are some sort of guru posing profound clues to some underlying false axiom of our understanding of the laws of physics.

For heavens sake man, ask questions properly and follow up with something logical because you really come across as bl**dy stupid at the moment.

 

[Grizzly]

... to assess whether or not everybody was aware that current will pass through the human body and that you can get a 'shock' from a 230v supply.
This may seem silly, but a number of contributors to this and the IET forum claim that this isn't possible!

No, David, no-one on either forum has said anything of the sort.
Your gross misunderstanding of what they have said has led you to this erroneous belief.
Your silly arguments and theories have been slapped down, again & again, wherever you've posted them, and still you post more drivel.
It was amusing once, but now it just seems pathetic and delusional.

 

[securespark]

Cockburn's grunting.

I'd be grunting if my c*ck was burning...

 

[securespark]

Using a neon screwdriver is safer than asking you all to touch an energised line circuit conductor, in order just to prove the point.

What point?

I'd like to think that all the professional sparks here and those who understand the principle of how one of these infernal devices works would not do either of those things, so to say it's safer is meaningless.

 

[sparkticus]

Cockburn's grunting.

I'd be grunting if my c*ck was burning...

He hasn't grunted for a day or two, let's hope he's electrocuted himself while experimenting with one of his stupid theories

 

[Grizzly]

... let's hope he's electrocuted himself while experimenting with one of his stupid theories

That would never happen to david911knobsinge.
Don't you understand, he's an expert at electricals!

 

[david911cockburn]

Grizzly,
Your hero OMS suggested that a women could not be electrocuted in a shower unless she was in contact with an earthed conductor!
That's just one example.

Bernard,
Your first entry suggested that a neon screwdriver would not work if the user was stood on a wooden floor, but your latest entry contradicts this by implying that it doesn't matter where the user is stood.

The chap who's client tested a copper pipe with a neon screwdriver and thought it was hazardous live,
If all of the accessible conductors within the installation were connected to the main earthing point of that installation (as per EAWR 1989 Reg.8), then an intermittent earth fault (such as this could have been) would automatically disconnect the offending circuit making diagnoses of the problem fairly straight forward. If on the other hand no circuit was automatically disconnected, you could say with all confidence that the neon screwdriver was just picking up 'earth leakage current' that is perfectly normal within a healthy system.