Bonding...!?

[ppppenguin]

The whole question of bonding was always a bit of a grey area and judging by this discussion it's still controversial:
http://www.theiet.org/forums/forum/messa...?catid=205&threadid=35917

For my own peace of mind I like all the metal bits I can touch to be bonded together, either via pipework or if necessary via explicit earth bonding wires. If you've got lots of plastic pipe in your system things can change a bit. For example if your bathroom basin is fed entirely by plastic pipework then it's more or less impossible for the taps to become live. Pure-ish water isn't a good conductor. Hence don't bond them.

[ed731pdh]

I guess at the end of the day it comes down to peace of mind, in that your living there and your not in risk of being wired to the national grid. Me personally, bond it completly, and move onto the next isuue in the knowledge of a job well done.

[ppppenguin]

Poorly thought out bonding can actually increase the risk of shock. An example. A metal kitchen sink fed via plastic pipes. There is a high resistance between it and anything else metal due to the water. Hence current regs say don't bond. If you manage to touch it at the same time as a live part there will be a minimal shock risk. If it was bonded you'd get a nasty belt until the RCD tripped.

[Mark Hennessy]

And that's the problem

Scenario: My shower is fed via a mix of copper and plastic pipes. It's gravity fed from the stored water, but assisted with a pump. When I refurb the bathroom, the last section of plastic pipe will be replaced with copper, but in the meantime, the metal shower valve and pipework that's visible behind the bath is not bonded. If I somehow managed to touch an exposed live part of the light fitting above and the metal shower at the same time, while standing in my plastic bath, I wouldn't get a shock. Well, unless I touched the bath tap, but that's less likely.

So, rather than bond the shower pipes post the short plastic sections, I'd much rather put an RCD on the lighting circuits.

Not least because bonding the chrome pipes that are visible above the bath would result in visible earth wires and earthing clamps (with their sharp edges, etc) - that's because the previous owners only ran the chrome pipes down to the level of the bath, and they are immediately connected to plastic at that point. So I'd have to replace the chrome pipes, or at least use compression fittings to convert them to a run of copper, only to have to go straight back to plastic. Or, I could just wait until we do the bathroom, and then it'll be copper all the way.

But I haven't bonded the pipes at the pump end, so currently my nice new copper runs from the adjacent room are floating anyway. As is the cold feed from the new plastic tank in the loft. The hot feed to the pump will be bonded (via the hot water cylinder and the boiler via the gas pipe), but the pump has plastic impeller housings and rubber connection hoses anyway! When we do the bathroom I might bond the 4 "incoming" pipes (hot/cold for bath/basin/bog and hot/cold for shower), and the cold is bonded in the cellar to the MET - though that would be under the floorboards, so not visible to a surveyor. But I really wouldn't want to do that until after I've put the lighting circuit on an RCD.

In other words, rather than slavishly following some "empirical" interpretation of the regs, I'd much rather think through the problem from first principles, and then see if my interpretation satisfies the regs. The regs don't require supplementary bonding in rooms that have RCD protection on all feeds. And *unnecessary* supplementary bonding can actually make things less safe. But that won't stop those who blindly bond everything because that's what every just does.