ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades PME and water pipe currents

And Paul, it sounds like your postal service has a tourist attraction and doesn't know it! I would love to ride that narrow guage under London. But don't let the Disney people know about it.

Karl

Karl,
As Paul stated in his post, here in the UK we have been prohibited from using the water pipe as the sole means of earthing an installation since 1966.

We are however required to bond all metal pipework in an installation to the main earthing terminal, regardless of whether the supply from the street is plastic or metal.

The requirements for this equipotential bonding have become increasingly stringent over the last 20 years or so. The minimum size for main equipotential bonding conductors to water, gas, heating, structural steel etc, is now 10mm for small installations up to 100A supply, but the local PoCo may require a larger size.

Supplementary equipotential bonding is required in areas of increased shock risk. In a residential situation this is bath/shower rooms, where bonding is required between the earthing terminals of electrical equipment & extraneous-coductive-parts (pipes) installed in zones 1,2 & 3.

Karl,
I checked up on the P.O. railway and it runs a little way north of Piccadilly Circus:


Have a look at the new thread Posted Here.

On the bonding issue that David has raised, it's also the case that our IEE Regs. always specified more stringent bonding requirements (larger conductors etc.) where PME was employed than with TN-S or TT systems.

In Ireland bonding of pipework is taken quite seriously too. You'll notice pretty heavy earth wires connected to straps linking pipework under most sinks etc.

It's always a good idea just incase anything does go wrong and part of the plumbing should ever become live.

I've heard that due to the use of the attic storage/buffer tank that having properly bonded pipework is even more essential (for other reasons) than in situations where the pipes are connected directly to a watermain simply for ground fault protection.

In a UK or irish house once the storage tank is full the entire plumbing system (typically all copper) could be completely isolated from the ground (the tank is more than likely plastic). All it would take is a water heater fault or a live cable to come into contact with plumbing for the entire system to go live. So at least if it's properly grounded and bonded there's no risk of getting a shock when you step into the shower!