Another strange fault...

[RF Lighting]

I got a phonecall from an electrican friend last week about an electric shower giving people shocks.

Here is the problem.

He had tested the shower with every test going, including striping the shower and IR testing each part. Circuit and shower all tested out fine for IR, Main incommer and shower polarity were fine, Ze and Zs within spec, bonding all good, RCD tested out ok and had not tripped, but testing between the CPC of the shower and the water coming out of the shower head was reading around 90V


I had a fair idea of what might be happening, and a not often used test confirmed it.

Any guesses?

 

[ericmark]

The first question I ask myself is could this happen with my shower. And the answer is yes. The shower head is not electrical connected to any thing so a wire within the wall could possibly be resistive or even capacitative connected.

However I don't use an electric shower.

However although I could maybe measure a voltage I would be unlikely to get a shock without tripping the RCD.

Of course you have one advantage you know what the voltage was compared to.

I have often wondered about metallic looking plastic bits where we assume metal to metal in error. The shower outlet in my house looks metal but is plastic so fixing screws could in theroy connect the thin plating.

 

[RF Lighting]

I haven't actually seen the fault my self, I was just helping a friend on the phone who was at his wits end.

The voltage was showing between the CPC in the shower and the water flowing from the shower head.

The CPC was proved to be healthy right back to the suppliers earth which was also fine. I beleive it was a TN-S supply. If not then it was TN-C-S.

 

[securespark]

Supplementary & PEB's both OK?

 

[Spark123]

Have seen it happen where a sewer runs parallel with an electric board earth, not a constant voltage though, just a belt every so often

 

[viewer]

Question: are we looking at "charged"water? The boiler is connected to CPC, but what happens to the water after that - plastic tubes with high velocity water?

 

[bernardgreen]

When you did the IR tests was there any water in the heater tank ?

Did you measure the water to CPC with a high or low impedance meter, did it dis-appear using a low impedance meter ?

In theory the last metal the water touches before leaving the shower is the heater tank which should be connected to the CPC. So there has to be a fault / problem / design error in the tank that creates the 90 volts in the water.

So my suggestion is that a live part of the element is in contact with water and a voltage divider from live to tank case through the water, ( but that should trip the RCD )

 

[ericmark]

I would be more inclined to look for screws holding the shower head hitting a cable in the wall than a fault with the shower.

It is surprising how high resistance water is and it would not need too much plastic between shower unit and shower head to mean the unit would not earth the head.

 

[skenk]

Shower was tested with 'every test going', so the 'not often used' test to confirm the fault wasn't just on electrical parts of the shower, right?


If so, then copper pipe feeding shower shorted to live but isolated from PEB by run of plastic (test for pd between pipe and cpc - not strictly a test on the shower but rather between shower and pipe)

Assuming high enough resistance to earth to prevent RCD trip



If not, then missing earth link in shower? (test for continuity between metal parts and earth terminal)

Current only flowing at point of electric shock (no circuit between showerhead and tray, internal cpc link missing) and not enough to trip RCD?


My guess(es) anyway

 

[dingodeano]

It's a power shower running off a combi?. Theres a fault water leak getting inside motor on terminals.

 

[ebee]

Plastic boiler tank , ins res down on electrodes to water in tank.
charged water leaving tank

 

[viewer]

C'mon Please tell us.

 

[RF Lighting]

What if I was to say the problem has been resolved, and no repairs were required to the shower unit or the circuit supplying it.

Also as a massive clue, it's a shower in a wet room with a tiled floor.

 

[SimonH2]

Does it have electric underfloor heating by any chance ?

 

[SimonH2]

Or, is it TN-C-S and a supply fault making the earth connection "live" while the floor is "earthed".