Shock off shower

[Justinsane]

Hi, a customer of mine phoned me the other night to say she had just touched the water inlet pipe to the shower and had a shock off it (she was in the shower at the time!)

I've been and looked at the job today and can't work out what is going on. I get a reading of 1 - 2 volts off the pipe whilest the shower is on. I also get this reading at different points on the pipework around the house.

Nothing when the shower is off. Surely this shouldn't happen but I wouldn't have thought she could get a shock off it....

I've check the bonding, its a TT system where a new c/unit has been run from the existing supply and the earth rod has been connected to the new box and then ran back to the old one. The installation is on a 100amp voltage controlled breaker and the shower circuit is on a 40amp mcb from the new box which has an RCD main switch. All pipework is bonded.

The loop reading from the shower is 181ohms.

Anyone got any ideas whats happening and why nothing is tripping....

cheers,
Justin

 

[Des 56]

The 1-2 volts that you are getting
Where or between what is this potential difference being measured?

 

[AEC]

Des 56

Was just about to ask that question.

 

[Jason Smith]

Firstly, where does the earth wire go from the old box ? - This sounds a bit strange on its own. First Job in that house is to do a continuity on the main Earth and bonding conductors. After completly isolating the shower of course. R1 +R2 of the shower circuit as Well. Have the front off the shower, you may find the answer stairing you in the face, however, there are further problems with this installation.

 

[Justinsane]

I have taken the front off the shower and the reading off the pipe was taken between the pipe and the neutral on the shower, (is this the correct way to test this?) Someone from the distribution company called by and took the readings from the other pipework using a clampmeter.

The original earth is a thin green cable which comes from the main breaker and would have originally been connected to an earth rod outside what was once the back door. When the extension was built this earth rod has been moved. A new c/unit was installed in the new extension fed from a 16mm submain from some henleys at the main box. The earth rod has been connected to the new c/unit and the old thin green earth wire has been connected to a new piece of wire and then into the new c/unt. Also a new earth cable has been run from the old unit to the new one. The bonding to water and gas is also connected to the new c/unit thus making this the main earthing terminal...it seems a weird way of doing things to me.

 

[Jason Smith]

So the old unit, feeds circuits in the old part of the house, the new unit is in the extension, Rodded, and the old unit is also rodded, correct ? - is there an old voltage operated breaker at the old board ( get that out !) and which board does the shower run off. Please give a bit more detail where you say the earth wires appear to be joited, thick to thin. It appreciate this is all hard to describein words mate !!

 

[Justinsane]

The main supply comes into the house where it comes from the meter through a 100amp voltage controlled breaker. 3 small green earth cables also come out of the consumer side of this breaker. 1 goes to the old fuse box, 1 goes to an old economy 7 unit which is not used (all the points have been disconnected around the house). and the other goes to the other side of the house where the extension has been built where it has been pushed up into the attic and joined to a 10mm (i think) earth cable with a terminal block and run to the new consumer unit in the extension.

The old consumer unit supplies the kitchen, bedrooms, main bathroom (without shower) and living rooms.

The extension was built to provide one bedroom and a shower room both supplied from a 5 way RCD main switch consumer unit.

The earth rod (there is only one) has been moved to out side the new extension and is connected straight back to the new c/unit where the older earth cable has been terminated (via its extension to a thicker cable)

There are two henley blocks splitting the l and n to a main switch which feeds the extension unit via a 16mm cable.

There is also a new earth cable run from the old c/unit to the new unit.

Bonding to the gas and water is connected to the new unit in the extension.

The wiring in the old house is old and messy. I have mentioned rewiring the old house but the customer doesn't want the expense, they just want it safe....I'm not sure I can do one without the other....

I tested earth loop from the shower itself and got a reading of 181 but not sure if this was through the pipework or the rod.

I need to go back and test all the bonding and main earth as you said.

Would this current be leakage from the shower?
The shower circuit is all new and fed from the new board with an RCD.

Are the old voltage controlled breakers dodgy?

I was going to suggest ripping out the old box and the economy 7 box and installing a new time delayed main switch supplying a new unit and the extension unit. Along with new earth rods for both c/units..

Is it possible to get the system upgraded to a PME? I have seen a couple of TT systems where they have literally split the neutral via a henley block and run an earth cable into another henley making that the MET and stuck a PME sticker on it...

 

[bugsy]

First thing you need to do is check the main bonding, equipotential bonding and supplementry bonding ,
once you have that sorted test the operation of the RCD.
If the wiring is that bad do a PIR , but by the visual report you've given sounds like a rewire.

 

[Deleted member 9648]

If there is a voltage operated ELCB it should trip if you do an earth loop on the shower....does it trip on the test button? Sounds to me like there is an earth fault somewhere on the installation and the failure of the main earth fault protection( ELCB) to operate is causing a voltage to appear on extraneous and conductive parts. You need to do an IR test on all circuits and clear any low readings and install an acceptable method of earthing.

 

[Justinsane]

The ELCB test button works but it didn't trip when I took the earth loop reading from the shower.
I tested the RCD on the new unit and it is fine.

The customer can't afford to pay for a rewire.

I suspect the problem is coming from the shower, but don't know why it isnt tripping.
Even if there isnt earth continuity on the pipework back to the box it should still trip shouldn't it?
A lot of modern installations use plastic pipes where the only bonding is at the entrance points to the building so showers , baths, sinks etc aren't bonded anyway.

There is an earth link within the shower itself between the cpc and the pipe.

 

[Deleted member 9648]

I doubt the problem is on the shower...(IR test on the element might prove otherwise)...if there is a working RCD protecting the circuit that should have tripped if there was any earth leakage....still think you need to IR test the entire installation and eliminate any low readings,and get rid of that ELCB which doesnt provide adequate fault protection.

 

[ericks]

Hi there Justinsane,
You most likely have a potential difference between ground and the tap. This means you have a bad earth to your installation. Knock in an earth spike close to your db or shower window. Test ac volts between the spike and the shower tap, or between the spike and the earth bar on your db. Make sure the earth spike is in wet soil or you can wet the area with a hosepipe. I would start with this test before cosidering changing rcd's and wiring. If you find a pd let me know and i can assist you further.

 

[Deleted member 9648]

Hi there Justinsane,
You most likely have a potential difference between ground and the tap. This means you have a bad earth to your installation. Knock in an earth spike close to your db or shower window. Test ac volts between the spike and the shower tap, or between the spike and the earth bar on your db. Make sure the earth spike is in wet soil or you can wet the area with a hosepipe. I would start with this test before cosidering changing rcd's and wiring. If you find a pd let me know and i can assist you further.

He knows he has a potential difference between ground and tap or the owner wouldnt be getting shocks.It will be because of a low IR to earth on one or more of the circuits in the house and inadequate earth fault protection....improving the earth is only part of the answer,you have to eliminate the cause of the potential difference as well.

 

[Justinsane]

Thanks for all the replies. The voltage reading on the pipework is only there when the shower is switched on which is why I thought it was probably the shower....The earth spike for the new part of the installation is about 10 feet away and the consumer unit it is connected through is less than that. There are only three circuits on the new part of the installation but all of the bonding is there as well...

I'm going back there next week and will do IR tests on all circuits (old and new) as well as continuity of bonding etc.

any further advice is well appreciated......

 

[Justinsane]

Well, I just tested the installation.

Continuity of the bonding is good, even though some of the cables are not the right size...
Bonding to water and gas all good.
IR tests were 500 megaohms on all circuits bar one. I had a reading of 256 between neutral and earth on one of the lighting circuits, I wouldn't normally worry about that...

There is no earth continuity on the two lighting circuits ( have removed two metal fittings)

Earth loop tests were all around 221ohms. They were 181 the first day i was there but i guess the weather probably affected that.

One thing though....the boiler has been getting an intermittent warning light stating reverse polarity somewhere in the installation which has been switching the boiler off.....I have removed all plug tops of every appliance in the house and they are all fine.

There is an old electric bar heater in the bathroom with a pull cord....looks well dodgy. The customer phoned me last night and she thinks that the boiler cuts out when this is switched on....is it possible that this would cause the shock in the shower as well? The ELCB can't be doing its job of this is the case....it works on its test button though........

A boiler engineer is coming next week week but I am completely lost.....

 

[Deleted member 9648]

The IR test results are fine but then it could be intermittent.....I still think the ELCB is unreliable, you should install an acceptable method of earthing and fault protection,with that in place and all bonding verified if there is an intermittent earth leakage the risk of shock will be greatly reduced.

 

[chris gray]

so there is the potential that the fault is on the load side of the bathroom electric heater? did you IR the load side?
DP sw?

 

[adversecamber]

I had a similar fault years ago at a friends house.

When the shower was on you could "feel" power in the taps and pipework, just enough to give you worryingly uncomfortable pins and needles, not like a real shock.

It turned out to be wet woodwork and damaged insulation causing it.

The power cable to the shower had been damaged when the house was built so the copper conducter was touching the wood of the partition wall that the shower was mounted on.
8 inches away the shower waterpipe was clipped to the same wood with copper saddles.

When the shower was used the water leaked behind the bath and made the wood wet (and conductive) causing the pipework to go "tingly".

I cant remember what trip was installed, but it didnt drop out.

It took ages to find as they only got me in to look at it when the shower hadnt been used and so the wood had dried out,so I couldnt find a problem.

it only went wrong after about 10 min shower use when the wall got damp.

 

[Justinsane]

I haven't tested the load side of the heater yet. I'm going back at the end of this week to remove the heater and change the elcb and the old consumer unit for a new one. Still not sure why she got a shock in the shower. The shower circuit is fed from a new unit with RCD protection.....

The fact that it is an intermittent problem makes it difficult to find......

 

[Jason Smith]

The shower circuit is fed from the new consumer unit with RCD protection, your saying as I would, that it should therfore trip. We need to think "outside of the box " on this one. We have got a very old house, a new system, and an old one. Heaven knows what has happened to the shower cable on its its run through history. Touching a hot pipe? a small nible from our rodent friends ? My first thought is to run a cable from the CU to the shower,yes, acros the carpets, then do a test. if the fault is cleared, the customer then cannot argue with the fact that the old cable has to come out and new one be installed properly. I think this test should be done first as a new cu may not standup with a known faulty circuit on it mate........