Neon screwdrivers

[geoff]

The corollary is also true

And ?

[newshound]

Well said. Did anyone actually answer the original question? The neon tube is in series with a big resistor, about 1 Megohm if I recall correctly, so that only a fraction of a milliamp goes through you; this does you no harm but is quite enough to light up the neon.

[The Medway Handyman]

I think I prefer 'no' electricity goes through you :-)

[Andy Wade]

That may help a little but you don't really need a conductive path to earth. The stray capacitance of the body to earth (~150 - 1000 pF) is enough to complete the circuit.

There are plenty of recorded cases of shock injuries resulting from neon screwdrivers. The are potentially dangerous because:

- the series resistor can fail short circuit, particularly the old type of solid cracked-carbon resistors they used to use in the things;

- in damp conditions the resistor can be bridged by condensation, etc.

- immunity to transient overvoltages (spikes and surges) is poor, and again the failure mode is to lower the impedance of the device, increasing body current;

- the neon tube itself can fracture if handled roughly;

- visibility of the live indication is at best poor in outdoor conditions.

OK, the last two points can apply to other voltage indicators, any type can fail to indicate, but (a) the neon screwdriver is far more likely to fail than an approved GS38-compliant indicator, and (b) test lamps and meters tend to fail high-impedance. As has already been said, the tester should be tested both before and after the test - this is the basic safe procedure for 'proving dead'.

[John Rumm]

Unless you are going to take up residence in a RF screened cage, that is probably not an option!

[John Rumm]

To be fair, you probably have enough free electrons floating about in you alone to look like a plenty good enough earth to one of these things.

The contact area of the stud at the top of the driver is probably small enough to not represent a direct electrocution risk, although you could get a nasty shock off it.

This is probably the most frequent failing...

Yup, good plan.

[Bob Mannix]

where are these cases recorded? I only ask as it is a well known usenet fault to say such a thing without any evidence to support a case! I have certainly never heard of one.

[Bazza]

I used to use one about 30 years ago until I received a belt of it, duly consigned to the bin. Nowadays I use a pen sized non contact tester for a quick check (always check it first with a known live)If it gives so much as a single beep out comes the meter.

Bazza

[Clint Sharp]

In message , Peter Twydell writes

Well, some would say that was the user's fault as the 24v one wasn't a neon but a bulb indicator (neons generally only work above 80-90V unless there's significant radiation or strong radio signals around) and the user should have known what tools he was about to use.

[Clint Sharp]

In message , robgraham writes

Yeah, I knew an electrician who used to do that (notice the past tense) he realised it was a stupid idea when he discovered that the extra wires were actually the other two phases for a three phase supply. Still, live and learn eh? Or not....

[Peter Twydell]

In message , Clint Sharp writes

I was that user. Can't remember exactly what the 24V one was as it's long been chucked out. It was very similar in appearance to the mains tester, which was the problem. Just picked it up without checking.

I *have* learned a little bit about safety since then; it was 37 years ago, after all.

[terry]

Hey you are right; I now recall once having a little screwdriver tester that must have had 12 or 24 volt bulb inside and a lead coming out top of the handle. Wonder where that is ................... maybe in one of the vehicles ................... or the garage .......... the boat .................. hmm!!!!

Back to a neon tester/screwdriver ..............; is not the reason they will usually light up even if one is NOT standing in bare feet on a wet floor, due to one's personal body capacitance to something (such as mother earth!) which is nominally at zero volts? At least seem to remember testing for 230 volts RMS in the UK doing that? In North America etc. where nominal RMS to neutral/ground is 115 RMS not so sure?

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Harry Bloomfield saying something like:

I've been known to light up in a field, too.

[The Medway Handyman]

With the smoking ban its the only bloody place you can light up...........

[Frank Erskine]

And then you'll probably cause a fire in the crops.

;-)

[www.GymRatZ.co.uk]

Actually the burning of stubble has also been banned for a good number of years now so it's a no win situation. :¬)

[PJ]

Shaving is far simpler. ;-)

[PJ]

Not a problem if the crop is tobacco.

[<me9]

What! This weather!

[<me9]

Candle and wet cloth.