Bathroom cabinet electrical shock?

On 28/05/2011 07:43, Dean Heighington wrote:

We will have to find something else to moan about then ;-)
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John.

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John Rumm wrote:

There's always something else to moan about ;-)
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Tim Watts

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On 28/05/2011 23:44, Tim Watts wrote:

Oh do stop moaning! ;-)
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Cheers,

John.

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On 28/05/2011 07:43, Dean Heighington wrote:

BTW, you might want to munge your "from" address to save collecting too much spam on it. This group seems to get scraped by a number of web based front ends looking for free content to sell adverts.
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John.

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Thanks. I do seem to have had more than my average spam quota of late! Is my 'from' now 'munged' enough? Btw: hope you don't mind the slight plagiarism for my real address? ;)
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On 29/05/2011 09:26, Dean Heighington wrote:

Yup, anything that alters it to a non working address will do. If you want folks to be able to contact you directly, then you will need some form of human readable address in a signature or similar.

Nope, help yourself ;-)
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John.

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On 26/05/2011 14:45, deano wrote:

Yup still here... (easy with a news reader ;-)

A couple linked to here:
http://wiki.diyfaq.org.uk/index.php?title=Newsgroup_access_tips

You could install a proxy like sygate or wingate on the PC, setup a port forward on your router and let the phone get to the virgin newsserver via that route.

No problem - glad it helped.
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John.

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Thanks, Newstap allows me to set alternative servers so I'll look to add some from here.

That would work at home but not for on the move.
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Dean Heighington wrote:

It might if you use dyndns.org
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On 29/05/2011 09:51, Tim Watts wrote:

Yup, if you have a static IP then it ought to work anywhere - the phone is told to go to a news server running on *your* PC. From there is gets redirected to the one available to virgin BB customers.
Without a static IP, then you can still get round it if your router can use dyndns - that way it maintains a name to IP mapping, and the phone can still visit a static "name" which will resolve into your varying IP.
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John.

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Hmmnnn. Now something else I'll have to try and do :)
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On 15/05/11 18:42, John Rumm wrote:

Agree and it's driving me nuts!
Deano - the way to fix this is to NOT use google groups. Try using eg Thunderbird and a free news server.
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On 15/05/2011 15:49, deano wrote:

here is that far up the stream, as the mains Earthing in the house has been in situ since I moved here, some 14 years ago and has been tested in anger IIRC at various times with short circuits and fuses blowing but I get that you're covering the bases and going to the worst case scenario, identifying the source.

I'd check the earth wiring from the suspect sockets back to the Consumer Unit earth bar.
If that had become disconnected, then any normal mains filters in the appliances that generate small leakage would cause the socket / cabinet non-earth to float to about 120v, but at high impedance, giving the tingle you describe.
--
Ron




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On Sunday, May 15, 2011 10:28:46 PM UTC+1, Ron Lowe wrote:

Doing that this morning... need a longer fly lead!

Wow... this is where I'd like to learn more about theory... 120v sounds scary, how does "high impedance" bring that down to just a 'tingle'?
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On 16/05/2011 09:10, deano wrote:

OK, let us know how it goes... (any spare wire will do - so long as you measure its resistance and take that away from your result)

For in depth theory, see:
http://www.allaboutcircuits.com/vol_2/index.html
A common design of input filter will have a couple of inductors inline with the L&N to act as chokes (inductors chosen such that they conduct very well at mains frequencies, and very poorly at radio frequency), and then usually a pair of capacitors connected between L & E and E & N. (and / or possibly one between L & N as well)
See the pic on the front of the filter shown here:
http://cpc.farnell.com/schaffner/fn-406-3-02/filter-3a-pcb-mount/dp/FT00707
Capacitors are like inductors in that their "resistance" (or reactance as its called when dealing with AC) varies with frequency. However their response is the reverse of an inductor - i.e. they totally block DC, and conduct increasingly well with rising frequency. So if you pick a very low value of capacitor and slap it across the mains to earth, it has almost no effect at mains frequency, but HF noise will be coupled to earth via the cap.
Say you take a suppression cap with a capacitance of 2200pF. The reactance will be given by the formula
Xc = 1 / 2 x pi x f x c
So at 100kHz the cap will look like 1 / 2 x pi x 100000 x 100 x 10^-9 approx 636 ohms. Hence it conducts and snubs the radio frequency quite well. However at 50Hz mains you get and effective resistance of 1.3M ohms.
So if you were to redraw your effective circuit you have your earth wire connected to L & N via a pair of 1.3M Ohm resistors. Since both "resistors" are the same size, if the earth is not connected to anything at all, it will just sit half way between the L & N voltage - or typically about 120V. However even in this circumstance the current that can flow to earth is tiny, if you do V = IR you get 230 / 1.3M = 0.18mA. So lets say your earth is not as good as it ought to be, you come along and stick your mit on the earthed tap, and the cabinet which is connected to the centre point of this notional resistor network, and you will get some voltage across you that you can feel. The maximum current that can flow through you is limited less than 200uA though.
--
Cheers,

John.

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That sure is some concise info there John- thank you for taking the time to write that. I have read it twice now and am starting to get the general gist although the physics loses me a bit for now :)
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On 16/05/2011 14:44, deano wrote:

The physics is actually quite easy to visualise if you think about it from the basic principles.
A capacitor is basically a pair of conductive "plates" separated by an insulator. When you apply a voltage across the plates, you see a some current flow briefly into it as it "charges up" (in reality you are storing a small amount of electrical energy in an electric field created by the plates - all the free electrons migrate round to one of the plates - leaving it negatively charged). You may remember physics demos with a gold leaf electroscope which shows how you can accumulate charge on a plate?
Hence with a DC supply connected to a cap, you get a brief flow of current as it charges, and then the current flow falls away to nothing. Since current can't pass across the insulating gap. If however you now swap the polarity of the battery, then you will again see a brief flow of current as you discharge it and the recharge it with the opposite polarity.
A cap across an AC supply thus looks like it actually conducts because the continual reversal of polarity of the supply allows it to keep passing current as it is charged, discharged and recharged in the opposite direction. How well it conducts is a function of how quickly you reverse the supply polarity (i.e. the frequency of the AC), and the size of the capacitor.
The larger the capacitor, or the higher the frequency, the better the conductance (or lower the resistance).
There are basically two common cases where this is going to be relevant in mains electrics. The first you have experienced first hand - capacitors in input filters will leak small amounts to earth. So in your case with no earth, you see bits of metal feeling live to the touch. Alternatively you can start to eat into the leakage allowed by a RCD and get an unexpected trip if you have too many of these things on one RCD.
The second one is with capacitive coupling, where you don't even have an identifiable capacitor as such. Long lengths of wire laying side by side will exhibit a tiny capacitance as well. If one of these is live and the other not connected to anything "solid" like L or N or E, then it will tend to appear to be live as well. This can fool some sensitive digital meters, or cause CFL bulbs to flash unexpectedly in the dark, or sometimes even give a tingle sensation similar to what you were experiencing.
--
Cheers,

John.

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Tumble Dryer!
Unplugged from utility cupboard = no tingle! Plugged into different outlet on other side of cupboard = no tingle!
or wall outlet where first plugged in???
or close proximity of dryer to cabinet???
Aaaah, it's like a dangerous version of pin the tail on the donkey!
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Washing machine plugged into original wall outlet (where tumble dryer was) tingle
So... wall outlet faulty? Loose connections? Will take a look!
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On 15/05/2011 13:33, Dave Plowman (News) wrote:

Even a poor earth should suppress any tingles due to capacitive leakage. That's not to say that a poor earth is in any way acceptable though. If the tingles remain I'd suggest checking earth continuity from the cabinet all the way back to the main earth terminal - use a multimeter and long flying lead if you haven't got a loop tester.
Deano, earlier wrote:

This is a 3-core flex, I presume? That's a rather basic question, but I don't think anyone else has asked...
--
Andy

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