DIYbanter - View Single Post - Bathroom Earth Bonding

wrote:
Feel free to shoot me down here, but I have just the same bonding
question. I have bonded all exposed metalwork together in the bathroom,
including to a cold water pipe. I don't particularly want to link into
any local circuits, I was going to take back to the TN-S earth point at
the CU.
Let the local circuits find their own earths back via the RCD/CU !

You run the risk then of (say) a CPC springing out of an earth terminal
and (either in the same place or elsewhere, downstream of the fault)
shorting to a live. This faulty-live-earth could then be taken into the
bathroom and make something live, eg the mounting screws of a flex
outlet feeding a double-insulated towel rail. You could then get a full
240V arm-arm shock from the live apparatus in one hand and the cold tap
in the other.

The point of equipotential bonding is to ensure that you cannot get a
potential difference. If you bond the cold tap to the CPC in the towel
rail FCU, you cannot get a shock *between the two*, even if they are
both live -- because there is no potential difference.

Anything conductive that comes into the bathroom ie could introduce a
potential must be bonded to everything else that might be at a different
potential, so there can be no potential difference. Because these things
usually include services like CPC and metallic water pipes earthed
elsewhere, the euipotential bonding will usually be earthy.

Owain