[Question] Earthing Extraneous Conductive parts

[Reginald]

Hello everyone. Its been a while since I posted anything but thank you for replies, I cannot begin to tel you how helpful they were.

I'd like to know something concerning Bonding of Conductive parts in an installation. SANS 10142 stipulates that hot & cold water pipes be bonded together and connected to Earth Continuity Conductor. My understanding is that ECC is a conductor used to carry earth fault currents/ leakage currents safely to ground. Now what on earth would make these pipes to become hot (alive)?
I might not see the the simple answer in front of me but if someone could clearify on this regard I'd appreciate it.

[Leecatt]

The insulation in the element in the geyser can fail and the water can transfer electricity into the steel pipes.

[gobbleteller]

If any live wire inside the roof had an insulation failure and it came into contact with any piping, the piping would become energized. Touching the tap or water would electrocute you. Bonding to earth will let current flow instead to earth and trip your earth leakage relay.

Similarly, a loose live wire in the geyser connection box coming into contact with the metal casing of the geyser will energize the piping.

Also, if not bonded to earth, lightning will energize the piping, taps and water

[Reginald]

The insulation in the element in the geyser can fail and the water can transfer electricity into the steel pipes.

One of this old house had a similar problem. Apparently a so called electrician had installed a new geyser and the owner of the house said, a couple of days after he couldn't touch taps, sink and geyser pipes because he was getting shocked. He isolated the circuit.
I checked geyser connections and they seemed to be fine, earth leakage connected and it wasn't tripping . I suggested that he must get a bonding conductor as the was none.
Could it be the elements insulation had failed as you say even if the geyser is new? If so can it be replaced? Or could it be another circuit leaking current to the pipes?

[Reginald]

Gobbleteller atleast that's what I thought with this old house having such problem.. that it could be current from insulation failure of another circuit as the geyser connections were correct with no loose connections. The earth leakage relay wouldn't trip though thus I suggested the owner gets a bonding conductor for gutters, roof, pipes etc as there was none.

[AndyD]

If you get a tingling or shock from something then there's two faults that need remedy. Firstly there's an insulation resistance (IR) fault that's causing the extraneous conductive item to develope a touch voltage and secondly there's no earth bonding that would prevent the touch voltage rising and also cause the RCD to disconnect the offending circuit (assuming the RCD is fully functional). Just installing bonding might prevent the tingling or shocking but the underlying cause will still be there if you don't fix the IR fault.

[skatingsparks]

Had this a few times. Often its that there is no proper incoming earth(from the supplier - bad cable joint in the road somewhere or at sub station or a little bit of copper theft) or the earth fault loop impedance is high so even when the is a fault to earth(as Andy says 2 faults) the fault current flowing is so low its not enough to trip the breaker.

Some dopey electrician come in and uses a multi meter and gets 220v between live and earth and "yes there is earth" but the shocks continue. Yes there is earth, those water pipes go into the ground and you get a kind of earth through the bonding and yes there is 220 between live and "kind of earth". I come in with my nice loop tester and find the external earth fault loop is high(or non existent). Not enough to trip the earth leakage but when the poor customer in question when he/she is soaking wet in a shower the resistance is a little lower and he/she gets a surprises.

First thing to check. Do i have an incoming earth(test with a proper loop tester not a multimeter). Then find the other fault.

[AndyD]

......Some dopey electrician come in and uses a multi meter and gets 220v between live and earth and "yes there is earth" but the shocks continue.

Yeah, this is one of my pet hates, incorrect use of test equipment and the user not understanding the characteristics of the tester and what it's actually indicating. The electrician you describe would be the same kinda idiot that can't understand why his digital multimeter shows 95v between a live that's been isolated at the circuit breaker and a neutral or earth.

Sorry, rant over.

[Sparks]

For sure, and then a 4th year electrical engineering student scares the living daylights out of his parents because he got a reading of 240 between neutral and earth too. Fortunately my old school buddy phoned me and not some guy out to make a killing off them because they were prepared to have me rewire the house! Just because the earth wires are connected to the pipes and the earth terminal in the roof does not meant it is connected at the DB neither, only a tester will confirm this. A floating earth has caused many a surprise.

[AndyD]

Floating conductors and 'ghost' voltages never used to be an issue in the old days when everyone was using analogue testers