How Does a neon screwdriver work?

[matt1e]

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.

example of what, may I enquire?
A correct statement?
unless she has the cover off of course and is playing with the live conductors
Please explain how she could be electrocuted in an installation that complies with bs 7671 otherwise Dave
oh, and hit by lightning ,electric eels thrown in the tray etc don't count

Give me one scenario!
then we'll start from there

 

[Grizzly]

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.

Bless you David.
You still understand nothing, yet parade your ignorance for all to see.
A truly deluded individual, a point all members of both forums agree upon.

 

[bernardgreen]

Please explain how she could be electrocuted in an installation that complies with bs 7671

Scenario

PME supply to the house.

Pipe work is connected to the MET so shower, water and pipes are at the potential of the incoming neutral.

Within reach of the lady in the shower is a non-bonded metal item that has a path to true ground. Metal waste pipe is one possiblility, damp walls that are slightly conductive to true ground is another option.

Local area three phase supply network becomes phase un-balanced and neutral incomer potential differs from true ground.

The lady now has true ground potential and neutral potential ( via bonding to pipes ) within reach. The neutral is un-likely to be more than few tens of volts above true ground potential but that is enough to give a noticable tingle or mild shock. Electrocution ( fatal or otherwise ) is un-likely but injury from in-voluntary reaction the the tingle / shock causing a fall is a possibility.

Total disconnection of the neutral in the supply incomer to the house will bring the now disconnected neutral in the house to full Live potential and the now 230 volts between pipe work and true ground potential could be fatal. ( live to neutral via appliances ).

 

[matt1e]

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.

Please explain how she could be electrocuted in an installation that complies with bs 7671

Scenario

PME supply to the house.

Pipe work is connected to the MET so shower, water and pipes are at the potential of the incoming neutral.

so that will be an earthed conductor then

Within reach of the lady in the shower is a non-bonded metal item that has a path to true ground. Metal waste pipe is one possiblility, damp walls that are slightly conductive to true ground is another option.

And that will be an installation that doesn't comply to BS 7671

 

[bernardgreen]

Does BS7671 actually mention damp walls and if so does it consider them as a hazard in that they are capable of bringing true ground potential into the equipotential area inside the building. ?

 

[JohnW2]

Does BS7671 actually mention damp walls and if so does it consider them as a hazard in that they are capable of bringing true ground potential into the equipotential area inside the building. ?

Not explicitly, to the best of my knowledge. However, the requirement for main protective bonding applies to all extraneous-conductive-parts, and they are defined as 'any conductor' (doesn't specifically mention metal) which is 'liable to intriduce a potential, generally Earth potential...'. I therefore think it is easy to argue that a sufficiently damp wall might qualify.

How one would bond the walls of an existing building is another matter!

Kind Regards, John.

 

[bernardgreen]

How one would bond the walls of an existing building is another matter.

Another thing the regs do not take into account. It seems common sense in this case to ignore the PME earth supplied and go instead for a TT supply. At least if the CPC is bonded to an earth rod the walls are going to be at the same potential as the CPC no matter what happens to the network / incoming neutral.

Or maybe not if a nearby property has PME with a metal water pipe bonded to the incoming neutral ( via the PME MET ). A neutral fault to that property could create a potential gradient through the ground and that could result in two damp walls of a house having diffferent potentials.

 

[JohnW2]

It seems common sense in this case to ignore the PME earth supplied and go instead for a TT supply. At least if the CPC is bonded to an earth rod the walls are going to be at the same potential as the CPC no matter what happens to the network / incoming neutral.

Whilst that is true, there is unfortunately still a hazard in what you propose unless you can find a way of bonding the walls. Because of the relatively high impedance of a TT earth, in the presence of a L-E fault in the installation, the potential of the CPC will rise (at least briefly, until an RCD operates) to considerably above true earth potential (hence also relative to any damp walls which are presenting a 'true earth' potential).

Kind Regards, John

 

[viewer]

Can I suggest only those who take the "never assume anything" route may survive to draw a pension.
From my working life, I've seen a few instances of deaths or injuries due to scenarios suggested in the posts. The situations were clearly where installations did not comply; but they may have done before something went wrong (and they are from a few years ago). Not one contradicts the advice given, but that Murphy was an optimist.
1. Lady electrocuted in shower. Bath earthed. Fault next door. Water supply pipe live.
2. Excavations. large cable found. Foreman told contact MANWEB; don't touch by my colleague. Came back to find ambulance on site. Foreman told employee to hacksaw through cable. Man felt tingle and refused to go on. Foreman told him he was stupid. Foreman then showed that it was dead by jamming his neon screwdriver into cable. Severe burns but survived.
3. Lady electrocuted via washing machine. Faulty machine and no earthing to old 15A plug circuit.
4. Musician electrocuted with guitar/amplifier. In own room but joint coin meter. Not found for a while as every time someone put money in the slot the fly larvae were cooked and the process restarted.
5. DJ at PH electrocuted live amp and earthed microphone (or vice versa can't remember).
There was an aeronautical poster which said, "Flying is not inherently dangerous, but it is unforgiving" ; just change a word.

 

[david911cockburn]

Well Grizzly,
Let us start by saying that a shower can be surface fed, usually this will be via a 'chrome' piece of pipe, this chrome pipe will usually be supplied by a flexible pipe once it dissappears under the floor or above the ceiling.

Now all we need is a trail of leaking water from the line circuit conductor to the isolated piece of chrome water pipe, simple enough for you.

Are you also aware that in order to 'slap down' one of my arguements (on the subject of Table 41C) your hero OMS had to turn ohms law on its' head and claim repeatedly that an increase in resistance caused an increase in current flow!
To make it even more amusing, a number of his boyfriends came onto the IET forum and agreed with him. Were you one of them?

 

[stillp]

Are you also aware that in order to 'slap down' one of my arguements (on the subject of Table 41C) your hero OMS had to turn ohms law on its' head and claim repeatedly that an increase in resistance caused an increase in current flow!

No, he was trying to explain a positive temperature coefficient to you, but you were (or pretended to be) too thick to understand.

 

[matt1e]

Well Grizzly,
Let us start by saying that a shower can be surface fed, usually this will be via a 'chrome' piece of pipe, this chrome pipe will usually be supplied by a flexible pipe once it dissappears under the floor or above the ceiling.

Now all we need is a trail of leaking water from the line circuit conductor to the isolated piece of chrome water pipe, simple enough for you.

is this the scenario I asked for?

ok then we'll debate the 17th which you think are wrong?
so ok you have your not so conductive trail of water adding potential to the chrome pipe as per your theory
now where is the other source of potential difference that you will also need to be in contact with to electrocute you coming from?

Simple enough for you?
ps please dont keep me waiting for 2 days while you try and research an answer

Matt

 

[matt1e]

I'll help anyway
stone shower tray imbedded in ground floor concrete?
damp walls as bernard pointed out earlier?
all feasable
debate how the 16th is better than the 17th
or better still tell me how you would handle the installation
Matt

 

[matt1e]

Are you also aware that in order to 'slap down' one of my arguements (on the subject of Table 41C) your hero OMS had to turn ohms law on its' head and claim repeatedly that an increase in resistance caused an increase in current flow!

No not repeatably I think maybe once which should have been taken for the typo it so obviously was

 

[david911cockburn]

Hi Matt,

This was the whole point of talking about 'neon screwdrivers', I did suggest that all of you should stand on floorboards in your slippers take off a socket front and try putting the back of your finger on a line circuit conductor, in order to prove to you all that this will result in a nasty shock even upstairs in your house.
Unfortunately nobody seems to have taken up the challenge.
The neon screwdriver also allows current to pass through your body when apparently you are not in contact with earth, so is it a mystery or just the damp in the atmosphere?

How does fork lightning travel across the sky on a humid day?

Its usually pretty damp in a shower room, therefore I would expect plenty of current to be able to flow.

Whoever it was may have been right about OMS talking in terms of temperature coefficient, therefore my appoligies may well be in order. But he shouldn't keep trying to wind me up all the time he should just answer questions and stick to the facts, "oh you think so do you" and "I doubt it" do not constitute a technical debate.
In short the bloke is a bit of a ****!