shocking bathtub

[DP]

Client is getting shocks from the tap and shower scrren in the bathroom. I have measured (using a Fluke) approximately 10 volts ac. Previously, while attempting to bond the hot and cold pipes to electrical earth, electrical flow (presumeably from the switch plaster (metal) box) tripped the 6amp mcb as well as the elcb mains isolator.

Today, I was going to isolate lighting circuits from each other in order to locate cable that is causing the wall, around the bathroom light switch (located in the hall) to be live along with shower screen and the bathtub/ taps. Access to underfloor is not (at present) available but am working on it.

Views from reqular knowledgeable would be most appreciated.

 

[Big_Spark]

Water in the back of the switch? I have seen this in a similar situation. Unknown to the client the wall was not as sealed as they believed, moisture soaked into the wall and a small charge was flowing via the external switch to the cast iron bath and aluminium shower screen which were in physical contact with the wall.

Other causes could be a fixing screw penetrating the cable within the wall.

If the MCB is tripping there is a dead short there, however I would be a little concerned..another reason why I do not like RCD main switches, The MCB is the overload protection and thus should operate before the Main protective device, however with the RCD in place, the MCB is unlikely to operate, so there is certainly amis with the circuit and possibly the installation as a whole.

Depending on what you find, it may be worth advising the client to have a Inspect and test undertaken for the whole property.

 

[chowbasa]

I was getting shocks off pipes in my house when a water pipe was removed and changed to plastic, this pipe was the only means of earthing there was a metal plate at the front entrance but that had rotted away
Are you sure the earth is any good as it may be non existant I had a PME terminal put in by the REC this cured it cost me 70 quid though.

 

[Big_Spark]

Chowbasa, that is certainly something that he may wish to look into for the longer term and a very good point, but in this situation I think it is probably confined to the bathroom as he did not mention shocks from kitchen fittings, and usually a broken earth path will cause problems in both locations.

It is also why they introduced the idea of earthing all metalwork in bathrooms to the earth terminals of nearby accessory boxes.

 

[securespark]

I was in friends house when the plumber cut through the hot water pipe coming off the top of the tank. He got a really nasty belt off it, and all the lights in the house went dim.

Weird, hey?

 

[DP]

It has been fixed.

1mm T&E started at the switchplate in the hall, went through the wall, entered a conduit, went upwards to the loft space. Came out of the conduit to run across the beams to enter a termination box. Where the cable came out of the conduit, it appeared to have been damaged and contacting the metal conduit.
Rerouted the switch cable to the termonation box. Bathtub is happy now. So is the client.

 

[ban-all-sheds]

Would one of these

in the end of the conduit have prevented the damage?

 

[chowbasa]

Is the conduit not earthed then ?

 

[kendor]

I was getting shocks off pipes in my house when a water pipe was removed and changed to plastic, this pipe was the only means of earthing there was a metal plate at the front entrance but that had rotted away
Are you sure the earth is any good as it may be non existant I had a PME terminal put in by the REC this cured it cost me 70 quid though.

A good example, It is exactly for this reason why the regs mentioned not using services pipework as a method of earthing but merely that they should be bonded.

Diy'ers often make the mistake and don't understand the difference between Earthing and Bonding and think they can get a good earth by simply tapping off the nearest pipe.

Did you get a chance to measure the voltage present between the pipes and a reference? It would have been interesting to know how high a voltage it was.

 

[breezer]

Did you get a chance to measure the voltage present between the pipes and a reference? .

kendor, helps if you read origonal post;

taken from 1st post I have measured (using a Fluke) approximately 10 volts ac.

 

[il78]

Just to add another concern with regards to the ELCB, I was aware that these are not to be used as usually they are voltage operated rather than current, making them unreliable........

 

[Big_Spark]

Just to add another concern with regards to the ELCB, I was aware that these are not to be used as usually they are voltage operated rather than current, making them unreliable........

That is the confusion caused by various names to similar devices.

Many years ago there were FVOD, Fault Voltage Operated Devices, these were "banned" from being installed as of January 1985, however a couple of manufacturers had already started calling them ELCB's, confusing the industry as the original current operated ones were already called..ELCB's!!

Now the true FVOD ELCB's are no longer sold, and haven't been for nearly 20 years, however, ELCB's still exist, these are also referred to as RCD's

The problem comes from the way in which manufacturers actually get the devices to operate. Without getting into a long discussion on this, and boring the cr*p out of everyone, ALL Current operated devices measure the voltage on the three conductors (If DC sensing). It is from the voltage they calculate the current flow, and thus whether it is within accepted parameters or not.

It is this that contributes to the confusion, as some manufacturers state that their kit measure the voltage, others do not, so many think it works simply by the voltage, when it does not..technically..but they all do..technically


Confused...welcome to the UK Electrical Industry!!

 

[securespark]

Thanks for that FWL!

I think that's made everything crystal in everyones minds......NOT!

 

[kendor]

Did you get a chance to measure the voltage present between the pipes and a reference? .

kendor, helps if you read origonal post;

taken from 1st post I have measured (using a Fluke) approximately 10 volts ac.

Here we go again! breezer read what i said again! He had already mentioned 10 volts ac but was talking about taps and the screen i specifically was asking whether he'd had a chance to test the volts across the pipework and reference (sorry if the word "reference" confused you, electrician's will know what i'm talking about)aswell as i'm more concerned about the fact it was taking out an mcb!!??