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Topic Title: Earth path
Topic Summary: shower fault
Created On: 03 October 2010 11:54 AM
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 03 October 2010 11:54 AM
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Zs

Posts: 2631
Joined: 20 July 2006

Hi all,

Can you explain something for me....

Customer called to say she was getting electric shocks from her shower hose and bath taps. Her husband said she was making it up. I rushed round expecting to find maybe a bonding issue and a fat man with a thin wife.

Both slim.

First of all we had a small spat as I refused to take off my boots. I have those blue shoe covers for indoors.

With three votsticks in my left hand I touched the shower hose with my right hand and all three sticks went bonkers in my other hand. Even the less sensitive Fluke one went off and also when held about 6 inches from the shower hose and the taps. Those of us who use the fluke voltstick will be aware that it takes a lot for it to go off at a distance. anyway, this isn't about voltsticks.

The shower, a power shower drawing hot water from the tank, was full of water and all the pipes in the house were live.

Once it was apart I found that the single RCD in the airing cupboard took 60mS to trip on x 5 as a first test. Too slow. No other RCDs in the house and old rewirable fuses.

No gas or water bonding.

NO EARTH CONNECTION TO WHAT LOOKS LIKE A TNS. Horrified. I can see the lump where it used to be. Must have been like this for years.

My question is this..

If the house had had no water/gas bonding but had a decent path to earth through the TNS, or other means, would this have been more likely to be fatal?

My Dad and I sat and drew faraday cages over a restaurant table last night, Mine just a circle with a stick man in it and his of course a cube with a bolt on lid and a mat underneath it and directional flow indicated etc. We got ourselves totally confused.

So I'm asking you.

And oh, I issued a humdinger of a danger letter.

Zs
 03 October 2010 12:12 PM
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alancapon

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Where we come across this, we have two options before we leave site. Either to isolate (which only the DNO can legally do) or fit a temporary front-end 30mA rcd.

In terms of the bonding, it would be far safer with bonding, as everything rises in potential together, there is therefore a reduced chance of finding things at different potentials to hold at the same time.

Back to papering the ceiling in one of the bedrooms . . . .

Regards,

Alan.
 03 October 2010 12:23 PM
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slittle

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Zs,

I've had the a similar one, TT supply NO rcd, customer claimed to be getting shocks from shower ??. The only difference was this was a "water shower" fed from a combi

Done the same as you, voltstick etc, nothing. Went through the whole "what else was switched on" thing. Eventually got down to well I normally have a shower at night. Lights I thought, and after a look of looking around found a L-E fault on the kitchen light fitting.

This was obviously causing the some of the pipework to rise but with no RCD the fault wasn't good enough to clear a 3036 fuse. I'm guessing the wet shower tray, concrete floor etc provided a reasonable route to terrafirma so hence the sensation.

Fitted RCD, cleared fault everyone happy.


Stu
 03 October 2010 01:05 PM
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John Peckham

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Zs

1st thing can we establish they were the pink boots?

2nd thing for heavens sake don't test for live parts with your hand even if you have a volt stick(s) in the other hand.

I had something similar yesterday. A house where the occupants have been receiving shocks when touching the taps and pipe work in the kitchen, dishwasher and washing machine. This has been happening for 4 years! Clearly not a man hazard but hazard for the wife. One of my 2382 students visited to fit a boiler in the kitchen and received a shock. Urgent call to me.

I entered premises and asked lots of questions of owner before entering kitchen to gain history of events.

Washing machine and dishwasher plus other appliances plugged in to sockets. Using socket adaptor measured voltage between pipe work pipework and socket earth pin and found a PD of 135V. Martindale in to socket and bleeping and light indication of earth fault. Isolate installation at the consumer unit. Long lead test from MET to kitchen pipework and good continuity although no main bond to gas and water, boiler CPC no doubt provideing earth. Long lead test to kitchen sockets and 2 sockets earthed and all the rest including the washing machine and dishwasher sockets unearthed. Socket fronts off and found DIY/kitchen fitter wiring. CPCs connected to back box and not to socket fronts. All sockets wired as a radial from a ring. 1st 2 socket earth continuity on CPC and then break somewhere in wall or floor above after that. Also found JB below kitchen unit feding unglanded SWA to shed also not earhed. Disconnected unearthed parts of the radial to make safe. Advised owner to have kitchen rewired. New dual RCD consumer unit and bonding. To use an Approved Domestic Installer etc.

The shocks I think came from touching dishwasher or other unearthed applainces and sink, boiler and pipework and getting combined earth leakage from the appliances.

In your case Zs with no bonding and no earth connection the pipework and/or exposed connected parts may have a potential difference so hence shock from appliance/shower earth leakage. If everything was unearthed and connected together you would not get a shock as there would be no, or minimal, PD ie earth free equipotential bonding. The problem with this and your house without any bonding or supplementary bonding you won't have an equipotential zone. You will also have a PD from the unearthed parts and the general mass of earth.

Your dad me be right about increasing the danger of connecting an earth under these circumstances but I would not want to take a shower with my feet in the water and touching the pipework with or without an RCD.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 03 October 2010 01:49 PM
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ant1uk

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Originally posted by: John Peckham

I would not want to take a shower with my feet in the water and touching the pipework with or without an RCD.


Reading that bit sent a shiver down my spine.....

Regards
 03 October 2010 02:00 PM
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GeoffBlackwell

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With three voltsticks in my left hand I touched the shower hose with my right hand and all three sticks went bonkers in my other hand.


Which only goes to reinforce my major objection to these devices - I often ask people who advocate their use - would they ever use them to 'prove' dead - oh no we never do that. So when they are up a ladder and the volt stick is the only thing handy what do they do - go on guess .

I was given one at a Megger bash the other day and I must have left it on my office desk. I later found it in the waste bin. My two and half year old grandson had been in the office and he must have decided that was the best place for it - he may go far in the electrical industry one day .

If the installation is not effectively earthed it is potentially dangerous - whether it is actually dangerous depends on the circumstances pervailing at the time. Is there a fault, is there a point of contact to the general mass of earth, etc, etc. - but this is a lottery, and its one you don't want to win .

I am not sure why you were drawing Faraday cages, they rarely help as for internal faults - bonding does not 'bring every thing to the same potential'. There is the little matter of the touch voltage.

This is: Vt = If * R2 volts in a bonded installation, higher if it is not bonded as you also get the voltage drop across the supply network earth path (yes the bit outside the house).

Regards

Geoff Blackwell
 03 October 2010 02:08 PM
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slittle

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I'll admit I missed Zs's left hand/right hand trick.

As much as some don't like them, I think a volt stick in these circumstances could at least prove that there may be something there but I'd want the volt stick in my left hand and not touch anything.

Failing that a decent 2 lead device such as the fluke and a known earth reference (screwdriver and long lead) because in these sort of faults it's often hard to establish what is "live" and what is earthy.

A colleague of mine had a nasty experience a few years ago when attending a site with reports of "shocks from the fridge", he got a little closer to the fridge than he planned (the story is he got knocked by a dog) and found out first hand that indeed the fridge was live...

Stu
 03 October 2010 05:06 PM
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Zs

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That was no trick Stu, that was a scary moment not to be repeated. That hose was covered in some kind of see through rubber and I was moving it to get the shower head out of the way.

I do fall into the voltstick camp though and have several. The only test I did once I'd seen them glow was with an old test lamp which I was given. I like the fact that a test lamp does nothing more than light up a lamp and requires a complete circuit. But the voltsticks are superb little indicators which don't require a complete circuit and that, I like. Remember the whole house of volstick lighting ceilings that turned out to be inductance through the celotex? But for a toddler I'd say they're a real sonic screwdriver

Anyway, pick up many of the technical books and start to read about equipotential bonding and the name Michael Faraday pops up within a few paragraphs. My Dad's argument was that his cage was insulated from earth and everything else and therefore not a good illustration of what we deal with in a normal installation. Mine was weak in comparison but from text books.

'And of course in a correctly bonded installation we live and/or work in Faraday cages' That's a Brian Scaddan quote so you can see how easy it is to believe.

I think John has hit on it being an earth free equipotential zone ( if it had bonding) without connection to earth proper. Bearing in mind that I had let the water out of the shower control in order to get to the connections we'll never know if the connections were immersed or just damp. I'm very surprised it didn't take out the fuse.

Zs
 03 October 2010 05:18 PM
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slittle

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My apologies, the way it was written it read that you had a voltstick in one hand and for some electrifying reason decided to grab the shower with the other.

I'm a voltstick man and always keep one in my pocket as a last check. That said my pet one (fluke) has gone missing since my fall and excursion to hospital. I think I gave it to the wife whilst in a&e as I figured I wouldn't need it for a few days. Four months on I can't find it so now I'm almost back on the road it's time to treat myself to a new one.


Stu
 03 October 2010 05:19 PM
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John Peckham

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Zs


Us new kids love our voltsticks. The old tuskers hate anything new. However I did get a certain well known old NICEIC presenter to get a Fluke voltstick.

GB has his golden spanner loop/PFC tester and battery and bell continuity tester and no doubt a 15W pigmy lamp in a lamp holder with a bit of black and red 3/029 attached as a volatge tester?

So come GB tell us what is wrong with a good quality voltstick? You might want to retrieve that Megger one from the bin. I did get a free Megger one at a Megger event but it does not bleep.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 03 October 2010 05:33 PM
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tonyericsson

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Originally posted by: Zs



My question is this..



If the house had had no water/gas bonding but had a decent path to earth through the TNS, or other means, would this have been more likely to be fatal?



Zs


No, the RCD would probably have operated.
 03 October 2010 05:48 PM
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John Peckham

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Tony

There was no RCD.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 03 October 2010 05:54 PM
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tonyericsson

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Hello John

from OP
Once it was apart I found that the single RCD in the airing cupboard took 60mS to trip on x 5 as a first test. Too slow.
 03 October 2010 06:19 PM
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ant1uk

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I recon its a 100ma RCD
 03 October 2010 06:32 PM
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daveparry1

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Nothing wrong with a decent quality voltstick, I have the Fluke one that flashes and buzzes, I always test it against a live conductor before using it to prove dead though, although tbh I usually use it to prove live! It's like most things in this game, having the experience to interpret what the tester is telling you,
Dave.
 03 October 2010 06:36 PM
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sparkingchip

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If the main earth was connected then the gas and plumbing installations would probably have been earthed by the CPC's at the boiler, immersion heater etc and the problem of raised voltage may not have occured, not really safe without the main bonds though.

I have a door bell wired up as a continuity tester in the van, it is very useful at times. I also have acquired three volt sticks, the fluke being a free gift, again they have their uses, but I would trust my life to one.

If Zs had died at least she would have gone out with her boots on, personally I would have used a volt stick to push the hose across rather than touching it having been told there is a problem resulting in receiving shocks from touching the shower, do the pink boots have a higher resistance to earth than the black ones?

Andy
 03 October 2010 06:49 PM
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GeoffBlackwell

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There are a number of issues here so let us try and look at them separately.

1
Customer called to say she was getting electric shocks from her shower hose and bath taps. Her husband said she was making it up. I rushed round expecting to find maybe a bonding issue and a fat man with a thin wife.


Now one person's near fatal experience is another person's trivial event - the problem is we don't know at this stage if she had received a potentially fatal shock or just a tingle.

So some detailed questioning is required to try and establish the facts. Of course you could ask her to demonstrate - but I wouldn't as she might just get lucky next time.

It may have been a minor tingle due to contact with a small voltage or it may have been potentially much worse.

2
The shower, a power shower drawing hot water from the tank, was full of water and all the pipes in the house were live.


So now we have the volt stick problem - when you say all of the pipes are live - what do you mean. i.e. Live according to a volt stick - or really live, and if so, with respect to what - earth maybe.

I normally trot out the tail about the Transco man at this stage so why change the habits of a life time.

I was called out one Saturday by a contractor that I do some work for. He was at a maisonette above a shop. It was one in a row.

The occupant was a young mother with a young baby - gas cooking and gas heating. The Transco man had seen his volt stick light up when he passed it near the gas pipe. His response was to cut the supply off and leave site - nice.

The contractor had the CU in bits and had tested everything including his apprentice .

A quick look out side revealed a shared metallic gas service and a TN-C-S system to each dwelling which effectively created a situation where the supply neutral and the gas pipe are in parallel. This means that the pipe will carry some neutral current through its bonding connections in each dwelling.

This is a common problem in tower blocks and sometimes the DNO might ask for insulating sections in each gas pipe. It would also affect any row of dwellings with common metallic services that are on a PME network. Less common these days as metallic services are on the way out.

We eventually got the Transco man back to site and after a great deal of argument during which I measured the current flow in the gas service (a few milliamps) and did various other tests to try and convince him that his volt stick was leading him astray .

I finally got him to reconnect the gas after I insisted that he test every other property and told him that he would get the same result so he would have to cut then all off.

So we need to know exactly what you mean when you say the pipes are live.

We have to determine if there is a fault, and if so, how dangerous is it.

The fact that there appears to be no earthing or bonding also needs to be dealt with, but determine if we have a possible immediate danger first. Alan's suggestion of an RCD is good and the NICEIC certainly used to give similar advice. However, if there is a fault it won't stay in so deal with that first.

Regards

Geoff Blackwell

Edited: 03 October 2010 at 08:18 PM by GeoffBlackwell
 03 October 2010 06:55 PM
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tonyericsson

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Originally posted by: ant1uk

I recon its a 100ma RCD


why?
 03 October 2010 07:08 PM
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ant1uk

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Originally posted by: tonyericsson

Originally posted by: ant1uk



I recon its a 100ma RCD




why?


Just a guess as the OP didn't say if it was a 30ma, and because his 5x test was over 40ms although it could be possible to be a faulty 30ma RCD, which would have nothing to do with the shocks anyway

Regards
 03 October 2010 07:11 PM
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sparkingchip

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The gas man may have a LV50 which is more sensitive than most volt sticks in use so adding to the confusion.

Andy
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