I just wanted to add that my ever present questioning of the value of equipotential bonding has led me to concur that bonding is not safe and it would be better to not bond anything at all. I believe in theis case that had no bonding been in place Emma Shaw would still be alive. A bold statement to make but true.

Don't be silly - it would need what is effectively an all insulated system to save Emma Shaw from this fault

Draw out the circuit paths - the victim would have received a shock if she touched any earthed metalwork - the HWS cylinder, hot or cold pipework, a class 1 appliance with a functioning CPC etc etc

Are you seriously suggesting that the solution would be to remove earthing and bonding from the system (and to eliminate naturally earthy components as well).

If you doubt the value of both main and supplementary bonding, then do a bit of basic research into the concept of touch voltage - then tell me it has no value - and I'll tell you in no uncertain terms that it has significant value.

As a starting point, the touch voltage driving curent through the impedance of the human body will be

Vt = If x R2

Then think about what R2 comprises - as a hint it is the resistance of the CPC back to the point of equalization (ie the point of bonding)

Now take a TN or TT system and determine that with our without bonding If won't change mutch - but R2 changes from just the impedance of the CPC within the building to the impedance of the CPC both within the building and the earth path outside the building right back to the transformer.

At a simple level you should see that if we multiply If by a bigger number then Vt must increase ?

Regards

OMS

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Let the wind blow you, across a big floor.

My eldest daughter and her partner have just bought their first flat on Monday of this week,the plumbing and electrical systems are identical to that in Emma Shaw's flat.

I'd better be a good dad and run some tests then upgrade the level of RCD protection, as only the sockets are protected, also show them the main switch, so if there are problems they know where to turn off the electric supply to the whole flat.

Andy

OMS you are more educated than I so I will talk in simple layman's terms as to how I see this.

I understand the need for earthing. All circuits are earthed and the main earthing conductor completes the earthing of the circuits. The part where I disagree is bringing extraneous-conductive-parts in to the electrical system by placing bonding conductors on them. It is pure theory is it not that this earthing system comprising of earth, main bonding and supplementary bonding makes parts that would not otherwise be part of the electrical system safer if they do inadvertently acquire a voltage through a fault. It is a well known fact that CURRENT causes death not VOLTAGE. A voltage can be present on something but current will only flow if a circuit can be made. 50mA of current is sufficient to kill. Merely touching a live part if no current can flow will not kill you but you will get a painful shock if the voltage is big enough.

The metal frame in Emma Shaws case was made live because the earthing conductor was damaged and voltage was present on the frame by virtue of the screw driven in to the cable. So the frame was then live but no current was flowing it was at 230V potential. When water was added to the scenario current was finding a path driven by the voltage (voltage is the force driving the flow) and multiple fault circuits were present in the area where Emma Shaw was. Some of these circuits were created by virtue of the metal pipework being bonded and hence giving low impedance paths for electricity to use. When Emma grabbed hold of the stop[cock to turn off the water she was literally grabbing a circuit that directed multiple fault paths through her body because the pipework was at 0V potential and she was the connection to complete another fault path. My contention is that had there been no electrical connection from the pipework to earth that she would not have completed a circuit. She would have felt a shock and painful one but not nearly as big as the one that killed her.

Now all of this is purely hypothesis and just the way I see it. I cannot back any of this up with calculations because I have neither the time nor the ability to do it. It is based on intuition and gut feeling.