Live bath taps

[gazza30]

I have done some tests today i banged a short length of copper pipe in the ground and connected a 10mm earth cable from it using that as the earth then tested the voltage from that to the cu earth terminal and the meter is showing 50v. The pme when disconnected from the cu is also 50v.
I then connected that earth to the cu just as a test and checked the bath taps there was no voltage present.
What would be the best thing to do as the house does not seam to have a true earth.

 

[plugwash]

it sounds like you have two seperate issues

1: it sounds like your main bonding to gas and water pipes isn't up to scratch. unless this 50V has a seriously low impedance then main bonding should bring your pipework to the same potential as the PME earth

2: it sounds like your pme supply is dodgy if you are measuring a voltage like that. it really needs to be checked out by the REC/DNO

 

[ban-all-sheds]

So much for the theory about water being non conductive then Re Bonding posts.

The comment was in relation to the posts in the past about necessity of bonding and some said that water can not introduce a hazard as it is not conductive enough but here is a prime example that it can conduct.

Now what does that point to? Water introducing a hazard?

There is only a short section of pipe which is plastic - we don't know how much, just that it is the "last section". It is a fact, accepted by almost everyone, that tap water in a 15mm pipe has a resistance of 115 kohms/m, so a short length of pipe, say 30cm, would have a resistance of 34.5 kohms, which could drop 200-odd volts when measured, and which could allow a noticeable 6mA to pass through a body.

Nobody has ever claimed that water can never introduce any hazard, nor that the presence of insignificant lengths of plastic piping means that supplementary equipotential bonding is not required.

 

[mapj1]

Ignoring all the snide comments about bacon rolls...
and getting our snouts back in the trough.
If you are sure your earth terminal at the meter board is tnc-s (PME) and really is at 50V with respect to a bit of pipe in the garden go no further. Step back respectfully away from all potentially live house metalwork, and pick up the 'phone (preferably a plastic one).
You need to call your DNO/REC , (probably not to talk to the "have-a-nice-day" girl you give the meter readings to, but a much rougher engineering lot ) and say :-
' my PME earth is 50Volts above true earth measured from a temporary test electrode outside- you are not providing a supply that meets the requirements of "Statutory Instrument 2002 No. 2665
The Electricity Safety, Quality and Continuity Regulations 2002" please come and make it safe'
http://www.pv-uk.org.uk/reference/grid_con/dno_map.htm should tell you who to call.
And PDQ they should send a clean shaven man round with blue overalls in a small van to take a look at it. They should not charge you for that - its their responsibility up to the terminal on the board, and yours there after.
He may just re-do some connections on the company side.
If it is really bad and he can't fix it from indoors then there will then follow succession of larger, and larger vans and less and less well-shaven men with bigger and bigger tattoos and louder voices and progressively ruder and ruder jokes until you have a pair of cloth sided 7.5 tonne lorries, a compressor pounding and arc-lights outside your window as what sounds like a team of about 20 navvies dig up the road outside through the night to find the loose connection in the street main...
This is exactly the reason I don't like PME, everything can appear to work, and still be in a potentially dangerous state..
In the mean time be very careful indeed what metal work you touch, and consider washing next door or outside.
Once that has been fixed, we can come back to the fact that the X bonding is a bit weak in the bathroom, and maybe needs up grading to meet latest regs. - but that's not their problem. In the mean time that poor bonding has probably reduced the shock you get to a safe level.
Actually it sounds like it is quite high impedance - if connecting to a temporary spike reduced the shock voltage to nearly nothing, but if you had had a faulty appliance plugged in at any time while this fault was present, it could be much worse.

 

[kendor]

So much for the theory about water being non conductive then Re Bonding posts.

The comment was in relation to the posts in the past about necessity of bonding and some said that water can not introduce a hazard as it is not conductive enough but here is a prime example that it can conduct.

Now what does that point to? Water introducing a hazard?

There is only a short section of pipe which is plastic - we don't know how much, just that it is the "last section". It is a fact, accepted by almost everyone, that tap water in a 15mm pipe has a resistance of 115 kohms/m, so a short length of pipe, say 30cm, would have a resistance of 34.5 kohms, which could drop 200-odd volts when measured, and which could allow a noticeable 6mA to pass through a body.

Nobody has ever claimed that water can never introduce any hazard, nor that the presence of insignificant lengths of plastic piping means that supplementary equipotential bonding is not required.

I feel like i've been vindicated

 

[ban-all-sheds]

How so?

The last I heard your policy was to apply bonding to items supplied entirely by plastic pipes.....

 

[Damocles]

Okay, the theory of bathroom bonding is to wire together everything earthy to ensure that they are all at the same voltage and you can never get the situation which you did get. Though arguably it worked, because although you could feel a shock you did not come to any harm. If all the current from your house is running back through the service bonding then there might be significant current in the bonding cables which could lead to voltage drops between different things. Considering you can feel the current produced by a 1.5V battery if you get a good connection with it, then this might explain some things.

If this is what is happening then you would expect the measured voltage to vary because it would depend on the exact current being used in the house at that time. On the other hand, it might be that earth and neutral have become separated. There may be a good return path via neutral for electrical equipment, but earth is floating. There could then be a high impedance induced voltage on the earth which you could feel or measure, but which was not dangerous in itself. The danger would be when the earth was called upon to act as an earth during a fault. Then it could simply become live.

Or it might be the supply neutral is badly earthed. The whole supply could be floating away from true earth despite your house being mostly wired correctly. Mostly, as somehow you did get a true earth into your bathroom and could measure the difference between this and your house earth. Which should not be possible if all external earths entering the building have been bonded. Interesting, eh?

 

[gazza30]

thanks to to all

I will get on the phone now and i will let you know what happens

gary

 

[mapj1]

In the mean time this leaflet http://www.rsgb.org.uk/emc/emcwebsite/leaflets/emc7protectivemultipleearthingmembers.pdf
Shows what I fear is possibly happening - the symptoms put tihs house in the'broken neutral' category. It is written for radio hams, but is valid for anyone with PME supplies who might mix mains supply 'earth' and real terra firma earths as part of their set-up..

 

[gazza30]

Had N.E.D.L out tonight to have a look at the pme they have said that the earth loop is testing fine at 0.21 ohms.
The engineer cannot explain why i am getting a reading of 50v of the pme to cu wire but did say that the earth from the pme to cu needs updating do to being only 4mm cable.
If i get this updated could this solve this problem as i am now going bald and have the wife on my ear.
I do not have much money so cannot pay for electrician to be here for hours at a time but need to get this problem sorted a.s.a.p.
is there anyway of getting this sorted without it costing a fortune.
.

 

[plugwash]

do you have any metal pipes running into the ground whatsoever and if so are they main bonded? (and i'm including things like metal waste pipes here).

it may just be local ground potential variations.

you really need someone who knows and understands what they are doing with theese things. I doubt most sparks or many low level rec guys do.

 

[mapj1]

Hmm well at least he came out quickly, even if maybe he did not recognise what he was looking at.
Where did the NEDL guy test between ? It should have been the live (probably from the CU) and the same earth terminal that is at 50V WRT true ground?
An impedance check alone is NOT enough - all that guarantees is that earth and neutral are connected together, not that they are actually at a proper earth potential.
Sorry to disagree with plug, but 50V is not an acceptable 'local ground variation' actually 50V is borderline between an extra low voltage and a potentialy dangerous 'low' one (in the legal sense that a 50V shock is deemed to be capable of killing you - you still have to be jolly unlucky)

Something is badly wrong with the supply, and it still sounds like the fault is not inside your house. By all means replace the 4mm wire with a piece of 16mm, but while it will bring you within the latest regs, unless it was actually not connecting properly before it won't actually make it any safer in this case. (if your meter has an ohms range you can confirm that it is not broken inside, but I'd be really surprised if it was)
Actually the other thing to confirm, though I'm sure from what you have described it will be true, is that the neutral of the supply (measure from anywhere convenient, like a nearby socket) will also be at 50V wrt a test electrode in the true ground.
If so I'd also expect your neighbours on the same substation to have the same problems - has anyone else mentioned strange tingles or discomfort while using hand held earthed tools out of doors. (this is when it is usually first spotted.)
You could add an earth spike of your own, and wire it into the main earth terminal too, and from what you have said that will reduce the fault voltage to an acceptable level, but you should not have to - the provision of an earth terminal within a few volts (less than 10) of true earth for a PME supply is the DNOs job.

Sorry to be so negative, but I fear you may have been fobbed off rather, or some part of the problem is not being correctly described
.

 

[gazza30]

Thanks Mike

The nedl bloke tested between the main fuse at the meter and the pme earth also at the meter (i think he wanted to go home as his wife was in his case).

Will replace earth wire and check next doors supply and see if there is a problem there and let you know the result.
If all else fails and can get no joy i will put in an earth spike.

 

[Panjandrum]

This is an intriguing puzzle, so I reviewed all the info you've posted. Still perplexed that you get anything from taps to water in a plastic bath with plastic waste that doesn't touch anything metal or any water elsewhere - but ignoring my perplexity.
Last mapj1 post makes sense (though not half as funny as his Tuesday, 1:52pm post).
A couple of points of clarification.
(17th, 10:50am) you'd connected independent earth to CU and the problem disappeared. Was pme earth connected to CU earth at that time?
(13th, 9:06pm) the voltage on the taps was still there when you disconnected bonding on the taps. That seems odd - or am I misunderstanding?
(13th, 3:06pm) sink taps and water inlet for the toilet are doing the same thing but the problem is only in the bathroom. Does that mean that you can also measure voltage between water in the sink and sink taps, and between water in the bog and bog inlet pipe (you would only get a shock from them if you had part of yourself in the water and touched the tap) - but you don't get anything like this anywhere else in the house?

 

[mapj1]

Glad to know I can inform and entertain simultaneously
The van sequence I have seen, not with electricity but with gas for my parents - we can smell gas, telephone nice man with minivan and suit sniffs, turns house off, waits and sniffs again, shakes head sadly and calls out transit van men who drill small holes in drive, and then shake heads etc. and call out the street main crew.. who come with 2 big trucks and compressor etc. I imagine its a similar hierarchy for the DNO for buried electric mains.
I did wonder, if the bath of isolated water is just a large body, with some capacitance to free space. Rather as the neon driver lights up when you touch it, even if you are on the steps. However, I'm assuming a high impedance meter, and no current flow to speak of, as I think a couple of hundred pF to ground would be the most we could hope for from such ana arrangement. (Note to self, next time I take a bath take the capacitor measurement box, and battery powered inverter.)
(second note to self remove inverter before getting in, or arrange to be dry cleaned only)
Whatever, if the taps and gas pipes are connected to the meter earth terminal, (but the street water and gas mains are plastic) and the meter earth terminal is connected to the supply neutral, but all of these are 50V above true external earth , then I can only conclude the fault is outside the building, and not his responsibility.
BUT I am still surprised - either someone is getting 190v when they should be getting 240, or the grounding at the substation has come unstuck, both of which I would have hoped the DNO man would have checked for.