Shock off shower

Justinsane · Mar 1, 2010

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

Deleted member 9648 · Mar 13, 2010

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 · Mar 13, 2010

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 · Mar 14, 2010

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 · Mar 15, 2010

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 · Mar 15, 2010

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........

Justinsane · Mar 19, 2010

Well I've think I've found the problem.....The electric bar heater in the bathroom (in the old part of the house ) had a live to earth fault when switched on. As this was on the old system it was making the earth bar live and therefore the metalwork bonded to it. The ELCB which was protecting the system wasn't tripping as the earth loop reading to the electrode was to high at 240ohms.

The shower wasn't tripping as the metalwork to it was bonded on the old c/unit not the new one.

I've disconnected the bar heater and ripped out the old fuse box and replaced it with a dual rcd board.
I've also installed a new earth rod and got the earth loop down to 135ohms. (although it was raining)

I'm going to bond the water pipe in the new bathroom (where the shower is) to the same c/unit which has the shower on and leave the rest bonded to the new unit i have just put in.

Should i try to get the earth loop reading lower? if so does anyone have any tips as to how?

cheers

marksparky · Mar 20, 2010

well technically ur reading is acceptable as the max ze for a tt system is 200 ohms although i know niceic's limit is 100 ohms im not sure about other scheme's, to get reading lower u put another rod in at least the length of a rod apart and connect 2 together or u could bury a earth tape if possible? hope this helps.