Shocks when touching shower thermostat controller and bath taps

[kels bels]

Hi all

I have a situation that I can't get my head around and hoping someone can help!

A client reported receiving shocks from her shower. When I visited the property, and when wet if you touched the metal parts of the shower (which was not electric), and the bath taps at the same time you got quite a shock from it.

There was no earthing system installed to the property. Nor was there water bonding or gas bonding.

They didn't want to get a TNCS system installed despite my recommendations, and asked me to install an earth rod which I did (ze 109 ohms). I also installed gas and water bonding. RCD protection to all circuits.

However, we still experienced the shock even with the earthing installed.

I did a bit of fault finding and turns out an 'unknown' circuit on a 6a MCB was causing the problem. When I disconnected the circuit, no more shocks from the shower/taps.

I thought installing an earth rod and water bonding would have stopped the shocks - am I wrong?

Grateful for any input. Kelly x

 

[Pete999]

Hi all

I have a situation that I can't get my head around and hoping someone can help!

A client reported receiving shocks from her shower. When I visited the property, and when wet if you touched the metal parts of the shower (which was not electric), and the bath taps at the same time you got quite a shock from it.

There was no earthing system installed to the property. Nor was there water bonding or gas bonding.

They didn't want to get a TNCS system installed despite my recommendations, and asked me to install an earth rod which I did (ze 109 ohms). I also installed gas and water bonding. RCD protection to all circuits.

However, we still experienced the shock even with the earthing installed.

I did a bit of fault finding and turns out an 'unknown' circuit on a 6a MCB was causing the problem. When I disconnected the circuit, no more shocks from the shower/taps.

I thought installing an earth rod and water bonding would have stopped the shocks - am I wrong?

Grateful for any input. Kelly x

You need to trace the "unknown circuit" and rectify the fault Kelly

 

[kels bels]

Yeah.... errr... thanks for that Pete. I did trace the unknown circuit, but it doesn't supply anything we can find inside or outside the property. So she was happy for me to disconnect it. Aside from ripping up the floorboards and opening up her walls I don't know how you would trace it and repair.

Thanks for your input, but I didn't actually ask what I should do. I asked why she was still receiving shocks when earthing was all installed.

I was wondering if it was because the earth was not good enough, or the earth leakage was very high and if that can happen.

 

[Plonker 3]

Did you use a EL meter to measure the leakage before and after the circuit was disconnected?

 

[valleybilly]

plastic pipe fittings on hot or cold between bonding & shower/bath to the fault maybe

 

[Darkwood]

I would physically disconnect the circuit let them know to report anything that no longer works to contact you, if a waste of time and money chasing ghost circuits if they can just be disconnected.

Look at the fault as a possible 2 way system as its very easy to look at it as going the obvious route but it could be possible the fault is actually in reverse in effect the tap may be live and your grounding it through the shower plumbing and not vice versa.

 

[Midwest]

Could be fault in cable buried in wall, live penetrated by nail or screw into wall. Shower outlet, could be picking up fault in buried pipe work in adjacent wall. With the faulty circuit reconnected, does it cause your new installed RCD to trip when touching shower & bath taps (using trailing lead, not human contact!)?

 

[Parker27]

'valleybilly' is along the right lines, do a long lead test to the furtherest point of the plumbing, I had a similar problem to this with a water softner connected connected across the mains and no continuity across the water softner, fixed it with 2 * earth clamps and a bit of 10mm.

 

[Farmelectrics]

strange why the rcd isnt tripping

 

[Plonker 3]

strange why the rcd isnt tripping

That would depend on the Earth Leakage.

 

[Paul P]

This reminds me of a fault i had Many years ago I was called to a similar situation. TNS system, customer was getting shocks off taps and pipes in a ground floor shower room. Carried out earth tests and found all pipe work was nicely earthed. After some head scratching we determined the floor was live and the Customer was earthing them selfs out on the pipe work.

We managed to get about 100v measured from the floor to a known earth, when we turned off the consumer unit it was still there.

After some more tests we finally traced it to a old lead cable going to the next door neighbours shed. Disconnected this and all was good. Thankfully they were ok with this.

The problem you have seems similar, a damaged live does not always have to go to a good enough earth to trip something. Even with RCD's

 

[Farmelectrics]

Is the rcd 30 mili amp or bigger as I presume it's now a tt system would that be correct

 

[snowhead]

strange why the rcd isnt tripping

The fault current is less than that required to trip the 30ma RCD.

I've only ever had 1 shock on an RCD protected circuit, it hurt and didn't trip, although the RCD later tested as O.K.

The O.P fault will have continuity between the Bath tap and the Live to the unknown circuit and as Valleybilly said above the tap and pipework won't be bonded.
The shower is the earth.

 

[Farmelectrics]

Ok question I thought limiting the current that's flows through your body. Ie 30 mili amp Is safe The op says people are getting tingles of the pipe and taps my question is what value ie mili amps would we actually get tingles from

 

[Richard Burns]

30mA is not safe, it is a level at which about 90-95% of the population will not die from experiencing.

1 mA Barely perceptible
16 mA Average “let go” threshold
20 mA Difficulty breathing
100 mA Heart “flutter” threshold
2 A Heart stoppage and internal organ damage
15/20 A ADS (average) opens circuit

Effects of current and time are shown in this graph within the AC-2 range, which is what we will mainly be concerned with regarding RCD protection, this varies from "Am I getting tingles" to "ouch that really hurt", but you will still have the chance to think this!