I recently had a porch built, but the builder disappeared without giving me the electrical completion certificate needed by the council. To address this, I had a periodic inspection report done.

The inspection reported two issues:
1. No equipotential bonding to the water and gas pipes
2. No RCD protection to socket circuit

The council aren't interested in either because they say these are related to the house as it exists rather than the porch, so everything is okay from that point of view. (its the original 1950s vintage wired fure box with the house wiring upgraded in about 1970)

I didn't know what equipotential bonding was, and this is the explanation I got from the inspector.

"In the event of a fault to earth ocurring in some appliance the earth potential will rise to approximately 240V. Without equipotential bonding, this means there will be a 240V potential difference between any earthed appliance and the gas and water pipes. If anyone was to touch the earthed appliance and, say, a tap, they would receive an electric shock. Equipotental bonding means that there would be no potental difference between the earthed appliance and, e.g., the tap, and so no shock"

I have two problems with this:
1. Surely the impedence of the earth cable will be approximately equal to the live, so at most the earth potential could be about 120V
2. You will receive an electric shock if you are standing in your bare feet in your living room and touch a live wire: surely equipotential bonding means that, under a fault condition, all the exposed metalwork in your house is at an elevated potential. While it might prevent a shock if you are touching both an appliance and, say, a tap, it could cause you to receive a shock if you are touching, the tap alone?

A second question relating to the actual implementation of the equipotential bonding. The inspector commented that it might be sufficient for the gas and water pipes to be bonded to eachother, but that was down to how the electrician doing the work interpreted the regulations. It makes sense that this would achieve the equipotential since the gas pipe is connected to earth by virtue of the earthing of the central heating boiler, but how can this be a matter of individual interpretation - either it is, or isn't acceptable under the regulations!