Shower Electric shocks but not everyone

[Roger]

Got a call today to go to a old flat as the lady was getting shocks when she was having a shower.
She explained that when she touches the tap and then the shower unit she gets a tingle and now here daughter is getting them as well.
Considering the property is a rental I was amazed to see a old rewireable fuse with some retrofit Wylex MCB put in there.No RCD ,bit of old twisted uninsulated earth wire coming up from the supply cable buried in the wall.The fuse box was not a stand alone type unit it was integral in a metal type service cabinet about 2 foot tall.
The property has an earth 0.6 (TN-S) however it only goes to power circuits,the lights have no earth and the circuit feeding the shower pump.Pulling of a cover in the cabinet revealed about 3 cables out of 8 actually had a cpc in them.
Incoming water is bonded ,but not gas to this flat and next door.Wondering around my R2 Long lead could get no continuity on any taps ,shower.
There is no supplementary bonding anywhere,lots of plastic unions so continuity if it was there is now broken.
The shower has a pump and the boiler is a conventional type with a hot cylinder upstairs.No bonding in the airing cupboard.
Now I assume she is experiencing a difference in potential which is why she is getting shocks.I could not get any shocks with the shower running and checked for any voltage present just with my volt stick and direct measurement,non existed.

But why does she get it and the previous tenant did not ?

Apart from saying the flat should really be rewired and it is not really suitable for renting i need to provide a detailed explanation as to what is going on and why it has not happened previously.

If i upgraded and put in main bonding to services and run upstairs to bathroom from MET,also supplementary bonding in bathroom under bath and sink and airing cupboard would that fix it.

She has just signed for 6 months so not really practical to rewire now,if he actually wants to go ahead.
Any help greatly received

 

[truckster]

Is there a metal waste to the bath? This could be bringing in an earth potential. Immediate solution would be to bond the bathroom and get an rcd on the place.

 

[Roger]

No metal waste ,all plastic.Having a look around outside bloody wires and cables everywhere.Outside patio ,decking on a flat roof all lights in twin and earth !.Old telephone wires all over the place.

 

[truckster]

Feel for you dude. Gotta love those slumlords!

 

[Roger]

I guess i could split the tails and like you say RCD the whole board.Nuisance tripping might be a problem as she sent me a text saying that the lights dimmers where staying on !
A right can of worms.
Do you think i am going down the right route and it is a potential difference that causes the shocks ?
Cheers

 

[truckster]

Almost certainly, it's just a case of finding out where thepotentials are coming from.

There was a case a few years ago where the foil on the back of the plaster board was the culprit, the lady had had some handrails fitted for her safety in the shower and they nearly killed her.

You could be there some time

 

[topquark]

First thing is I'd want to clarify the following with them. Is it that they are touching the tap and the shower at the same time, or first one then the other?

 

[Roger]

I am sure she said both,why ? although during all conversation she says its the shower head.

Under the bath the pump is housed and is feed from a fused spur (I can see it but whether i can get to it is a different matter to check it has a intention of having an earth) which goes back to probably a JB under the tiled floor ,then back to a 15amp rewireable fuse at the old sort of CU.The hot and cold feeds come up through the floor and then plastic speedfit and then back to copper for a bit then buried in wall is copper feeds to the shower valve.

I had thought that the shower pump might be causing a problem but they are so well insulated and with the lack of bonding i have gone down that route.The bath Tap is not pumped ,the pump only works with the shower.
Thanks

 

[topquark]

I am sure she said both,why ? although during all conversation she says its the shower head.

If they are touching the tap and shower at the same time then it's a most likely a live potential difference you're tracking down. If they're touching the tap followed by the shower (after breaking contact with the tap) then it may only be a static build up on the shower. Which might go someway towards explaining the "only happens now" bit.

If it's definately a tingle and not a sharp shock then it may only then be something around 50V so using a volt stick may not register the PD. They have their uses but not for this IMHO.

Is the shower an electric shower or just a boost pump fed mixer valve?

 

[pushrod]

I wouldn't offer to stick an rcd on the front of the installation until i had put an earth leakage clamp meter on everything to see if it is going to hold. You could be opening a big can of worms with the time honoured phrase of "it was working before" bouncing off your eardrums.

It sounds from your description that bonding everything in the bathroom should get all the metal work at the same potential and so stop tingles.

 

[Roger]

If they are touching the tap and shower at the same time then it's a most likely a live potential difference you're tracking down. If they're touching the tap followed by the shower (after breaking contact with the tap) then it may only be a static build up on the shower. Which might go someway towards explaining the "only happens now" bit.

If it's definately a tingle and not a sharp shock then it may only then be something around 50V so using a volt stick may not register the PD. They have their uses but not for this IMHO.

Is the shower an electric shower or just a boost pump fed mixer valve?

its just a shower booster pump to fed a mixer valve.

I am trying to jiggle a few things around so i can get back there tomorrow to carry out some work on the earthing and bonding.
I need to speak to the owner of the other flat as when i opened the service box for the gas meters ,one was very smelly.See what it smells like tomorrow.
Rusty old gas main,get me wire brush out to get a good connection.

 

[pushrod]

.

If it's definately a tingle and not a sharp shock then it may only then be something around 50V so using a volt stick may not register the PD. They have their uses but not for this IMHO.

?

Totally agree a volt stick is not for this job. The voltage you could be looking for though is likely to be more in the order of 1 or 2 volts as as a wet body could have a resistance in the order of 1000Ω and a tingle would likely be around 1 or 2 mA.

So V = I x R, = 0.002A x 1000Ω = 2V

 

[topquark]

Totally agree a volt stick is not for this job. The voltage you could be looking for though is likely to be more in the order of 1 or 2 volts as as a wet body could have a resistance in the order of 1000Ω and a tingle would likely be around 1 or 2 mA.

So V = I x R, = 0.002A x 1000Ω = 2V

I wouldn't suggest he does his testing wet

I doubt you'd get a resistance that low, but agreed that could in theory be a worse case.

Following that logic though the voltage you could be looking for could be as high as 230-2=228V to get a PD of 2V. Depending on what the potential is between.

 

[coomers]

if i were you i would suggest (and put it in writing)that a periodic inspection is carried out, she should of had one of these when she moved in from landlord.if the wiring is that bad i would not try to fault find in fact i would tell her NOT to use bath until full testing of all circuits and logged.
being the last electrician on site you are responsible and god forbid tingles off of taps become lethal you might have a lot of explaining to do.

 

[topquark]

I guess one of our assumptions here is that the bath is forming the return part of the circuit. It could either be at (or around 0V) or that could be introducing the potential to give you around 2V difference (so could even be a fault somewhere else completely).