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Electric shock from sink ? solution


 
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cape65

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Location: Edinburgh,
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PostPosted: Sun Jan 03, 2010 5:45 pm Reply with quote

My local water authority recently changed all the old metal pipes in my area to plastic. Since then I have sometimes been getting a 'tingling' sensation from my sink, dishwasher and washing machine. I'm thinking that they were probably earth bonded to the metal pipes and this is no longer the case. Can they be bonded to my gas pipes and how easy is it to do this? Thanks.
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electronicsuk

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PostPosted: Sun Jan 03, 2010 5:51 pm Reply with quote

I think it's much more likely that you have no main earth connection to your electrical installation, and in the absence of a proper earth, it had previously been provided by the incoming water main, which of course is no longer the case now that it's made of plastic.

If you want then you can take a picture of the service head where the electrical supply enters your property and your meter and consumer unit ate located and post it here, as this may assist in fault finding. However, your time would be better spent in calling out an electrician, as if the problem is as I suspect, anything metal in your house could potentially become live in the event of a fault.

EDIT: Have also replied in more detail to your duplicate topic in the plumbing forum.


Last edited by electronicsuk on Sun Jan 03, 2010 6:12 pm, edited 1 time in total
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BS3036

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PostPosted: Sun Jan 03, 2010 5:55 pm Reply with quote

Your cold water supply (within 600mm of where it enters the building) should be bonded directly to the main earthing terminal (near the consumer unit) using a single length of 10mm˛ cable. The same applies to the gas pipe. You are allowed to do this yourself.

Edit: electonicsuk has a good point about your original earthing. The picture could sort that out.
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TicklyT

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PostPosted: Sun Jan 03, 2010 9:03 pm Reply with quote

There are a few different earthing arrangements for electricity supplies. Sometimes the electricity supplier provides an earth connection, sometimes it's the customer, or, more properly, the customer's electrician who is responsible for providing an earth connection (electricians have the necessary test equipment to ensure the earth they provide is satisfactory).

It has not been permitted to use a gas main as the main earth connection for many years, but it is still necessary to bond both gas and water pipes to the main electrical earth.

A photo of the incoming connections may help identify what you will need to do.
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WabbitPoo

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PostPosted: Sun Jan 03, 2010 9:36 pm Reply with quote

non-parky comment coming here - int the main issue why the sink is live in the first place, not simply how it should be bonded?
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Hibbo

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PostPosted: Sun Jan 03, 2010 9:42 pm Reply with quote

The sink is (probably) live due to the lack of an incoming earth. There will always be a small amount of earth leakage (especially from electronic items like computers), but on an earthed installation this (small amount) of current is conducted away, and anything that is bonded to earth remains at earth potential. However (it sounds like) here there is no earth path (or a high resistance one) so the anything connected to the CPCs of the installation (like the sink or metal appliances) rises in potential - and gives a shock!

The shock is mild as the potential is only due to earth leakage, but should a live-earth fault develop then that there sink would be at 230v! icon_eek.gif
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RF Lighting

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PostPosted: Sun Jan 03, 2010 9:43 pm Reply with quote

It is most likely live due to the lack of any form of earthing in the property, and maybe some leakage or capacitance onto the no earthed CPCs rather than a physical fault on the final circuit wiring.

That said, the installation sounds to be in a very dangerous condition as it is and needs to be sorted ASAP.
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CO2000

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PostPosted: Sun Jan 03, 2010 11:27 pm Reply with quote

Our taps became live after a old Shaver socket failed & it gave the wife a fair tingle I can tell you !

She could feel it slightly through the running water from the taps.
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WabbitPoo

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PostPosted: Mon Jan 04, 2010 6:40 pm Reply with quote

My wife would surely like a right tingle - with my back? yeah right...
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bernardgreen

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PostPosted: Tue Jan 05, 2010 11:59 am Reply with quote

There is a logical reason to bond the water pipe at entry to the premises.

Water is a poor conductor but can carry enough current to provide a strong sensation of electrical shock. In extreme cases enough current to provide a significant shock resulting in injury can pass along the water in a plastic water pipe from one property to another. The dissolved salts in hard water make hard water a better conductor than soft water. Only distilled water is close to being a non conductor.

It is not im-possible that the water in the service pipe is at a voltage above earth due to a fault in another property that is served by the same water mains.

Or the water is at true earth potential but the earth potential of the electrical system is significantly above true earth potential.
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ban-all-sheds

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PostPosted: Wed Jan 06, 2010 11:33 pm Reply with quote

bernardgreen wrote:
In extreme cases enough current to provide a significant shock resulting in injury can pass along the water in a plastic water pipe from one property to another.

Only by applying a significant voltage, as Ohm's Law applies to water too.

A 15mm plastic pipe with tapwater in it has a resistance of about 100KΩ/m, and a 22mm one about 47K.

Do the maths on several m of pipe from one building to another...
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bernardgreen

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PostPosted: Fri Jan 08, 2010 8:39 am Reply with quote

I would be very interested to how those values were obtained. What area of test instrument electrode was in contact with the water at each end of the pipe.

Was that the highest or lowest value measured over the range of waters in the UK.

For computing current flow through liquids it is more common to use the conductance of the liquid in the calculations. Conductance is measured in units such as milliSiemens per cemtimetre cube and is almost equivalent to the reciprical of resistance. But resistance tends to be linear along a conductor while conductance is more applicable to the volume and dimensions of the liquid. The standard method is for a sample of the liquid to fill a test chamber that is a cube with sides of 1 cm by 1 cm. Two opposite walls are made of a conducting material and form the contact electrodes so the measurement is in effect along an infinite number of connections 1 cm long between the two electrodes where the total cross section area of those connections is 1 square cm.
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NotHimAgain

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PostPosted: Fri Jan 08, 2010 9:15 am Reply with quote

The figures probably originate from research conducted by the Electrical Research Assocation (now ERA Technology Limited).

The work was commissioned by the IEE.
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