Water pipe bonding

[ban-all-sheds]

A fault which places a potential on, say, a kitchen tap could in turn introduce that potential to the bathroom plumbing.

A fault does not make something an e-c-p.

 

[bernardgreen]

A fault does not make something an e-c-p

Of course it doesn't, but a fault could result in a fatality and therefor common sense would be to take steps to ensure as far as possible that faults are contained so as to reduce the risks of injury or death.

A couple of years ago after a plumber re-plumbed a house a measurable potential difference existed between two taps in the kitchen. It was due to capacitive coupling between pipes and cables, harmless but had pipe against cable resulkted in a fault that tap could have been Live with the other tap at Earth potential. Extremely unlikely that fault would occur but the cost of two Earth strap and a bit of cable to bond the taps together gave the owner peace of mind.

 

[RF Lighting]

So are you saying we should always bond metallic pipe work regardless of whether or not it is an e-c-p?

 

[EFLImpudence]

Of course it doesn't, but a fault could result in a fatality and therefor common sense would be to take steps to ensure as far as possible that faults are contained so as to reduce the risks of injury or death.

They are; we do.

A couple of years ago after a plumber re-plumbed a house a measurable potential difference existed between two taps in the kitchen. It was due to capacitive coupling between pipes and cables, harmless but had pipe against cable resulkted in a fault that tap could have been Live with the other tap at Earth potential. Extremely unlikely that fault would occur but the cost of two Earth strap and a bit of cable to bond the taps together gave the owner peace of mind.

As stated many times before, that risk is considered less than the alternative - touching a live conductor at the same time as an unnecessarily earthed pipe, tap, window frame, door knob, spoon etc.

There are the rules for bonding and earthing.
Thinking of one unlikely occurrence when these rules would be better ignored is not a valid argument.

 

[bernardgreen]

As stated many times before, that risk is considered less than the alternative

That argument has some validity, but tell that to the family of someone seriously maimed due to an incident that was caused by a "1 in 10,000" fault when 5 minutes and 50p of bits would have prevented that "1 in 10,000" fault going un-noticed and repaired before it was discovered when it caused injury.

 

[bernardgreen]

So are you saying we should always bond metallic pipe work regardless of whether or not it is an e-c-p?

No
But where two bits of metal ( hot and cold water taps ) are connected to copper pipes that dis-appear under the floor or into walls one trusts that the pipes have electrical continuity to some place ( hot water cylinder or combi boiler ) where they are electrically connected and hence can never have a potential difference between them.

Then the heating / hot water system is upgraded and plastic pipes installed around the place ( hot water cylinder or combi boiler ) where the "bonding" was located.

 

[EFLImpudence]

That argument has some validity, but tell that to the family of someone seriously maimed due to an incident that was caused by a "1 in 10,000" fault when 5 minutes and 50p of bits would have prevented that "1 in 10,000" fault going un-noticed and repaired before it was discovered when it caused injury.

That is most unfortunate but does not negate the fact that the alternative may result in 10 in 10,000 (I don't know the figure).

As with the MP's daughter; would you have advocated NOT earthing her washing machine?


I repeat:
Thinking of one unlikely occurrence when these rules would be better ignored is not a valid argument.

 

[ban-all-sheds]

Of course it doesn't

Then it does not get bonded.

End of.

Whatever else you said in your reply is wrong/misguided/superstitious/dangerous/irrelevant/any-or-all-of-those-(I didn't read it).

Seriously. Stop at "it is not an extraneous conductive part".

 

[PBC_1966]

With bits of plastic plumbing mixed with copper plumbing that potential could be on the cold tap while the hot tap is being held at ground ( Neutral ) via copper pipe to the hot water cylinder and it's earth immersion heater.

Indeed, with increased used of plastic couplings, plastic tap fixings etc. there's far more potential (no pun intended) for such things to happen than in the past when there was a good chance that every bit of plumbing throughout the house was all bonded together electrically.

 

[PBC_1966]

A fault does not make something an e-c-p.

Even if a fault causes that part to introduce a potential into some particular location which would not otherwise be there?

 

[EFLImpudence]

Indeed, with increased used of plastic couplings, plastic tap fixings etc. there's far more potential (no pun intended) for such things to happen than in the past when there was a good chance that every bit of plumbing throughout the house was all bonded together electrically.

I am not sure which such things to happen you have in mind.

More confusion has been introduced between main bonding (the OP) and supplementary bonding.

Bernard often speaks of pipes becoming live by coming into contact with a live conductor (this does not have to be considered in normal circumstances) rather than becoming live because of a fault to an exposed-c-p only until the OPD operates - when the pipe is already connected to a CPC of an appliance.

 

[EFLImpudence]

Even if a fault causes that part to introduce a potential into some particular location which would not otherwise be there?

As above, if it is not an extraneous-c-p it can't.

 

[PBC_1966]

I am not sure which such things to happen you have in mind.

As in Bernard's example. Say you have continuous continuity from the immersion heater tank to the hot tap, which is therefore earthed by way of the feed to the immersion heater, but plastic couplings have left that unbonded cold piping floating, or in reality earthed via the relatively high resistance of various stray paths through the fabric of the building. But if there's still a solid metallic path between the cold taps in different locations, something which livens the cold pipework in, say, the kitchen (a frayed kettle cord, perhaps) will leave the cold pipework at the bath live at 240V while the hot is still earthed by way of the immersion heater.

Bernard often speaks of pipes becoming live by coming into contact with a live conductor (this does not have to be considered in normal circumstances)

Why not? The possibility of a metal appliance casing becoming live that way is taken into account by requiring either earthing or double insulation.

rather than becoming live because of a fault to an exposed-c-p only until the OPD operates - when the pipe is already connected to a CPC of an appliance.

But if the pipe is earthed only via stray building paths, the OPD won't operate. Even an RCD might not (over 8000 ohms or so for a 30mA, 2400 ohms for 100mA etc.).

As above, if it is not an extraneous-c-p it can't.

If it's conductive, it can always introduce a potential into the area at one end of it if some potential is applied at the other end.

 

[EFLImpudence]

As in Bernard's example. Say you have continuous continuity from the immersion heater tank to the hot tap, which is therefore earthed by way of the feed to the immersion heater, but plastic couplings have left that unbonded cold piping floating, or in reality earthed via the relatively high resistance of various stray paths through the fabric of the building.

Well, if those stray paths cause the cold pipe to be within the limits to be considered an extraneous-c-p, although not likely, then, in a bathroom but not in a kitchen, supplementary bonding will be required.

But if there's still a solid metallic path between the cold taps in different locations, something which livens the cold pipework in, say, the kitchen (a frayed kettle cord, perhaps) will leave the cold pipework at the bath live at 240V while the hot is still earthed by way of the immersion heater.

That scenario is not required to be considered as it is deemed less hazardous than you touching the frayed lead and a wrongly bonded - earthed - isolated part.

Why not? The possibility of a metal appliance casing becoming live that way is taken into account by requiring either earthing or double insulation.

Because it is not an exposed-c-p as it is not part of the electrical installation.
If the kettle lead is trapped under the water pipe then you may consider the scenario likely and earth the pipe - or move the kettle lead.

But if the pipe is earthed only via stray building paths, the OPD won't operate. Even an RCD might not (over 8000 ohms or so for a 30mA, 2400 ohms for 100mA etc.).

Well, it is not a likely occurrence and, as I keep saying, that is considered less of a hazard than the opposite scenario.

If it's conductive, it can always introduce a potential into the area at one end of it if some potential is applied at the other end.

I refer the honourable gentleman to the reply I gave a moment ago.


What you are saying is only answered by reference again to window frames, door knobs and spoons.

Also, yet again, thinking of one unlikely occurrence when these rules would be better ignored is not a valid argument.

 

[bernardgreen]

Bernard often speaks of pipes becoming live by coming into contact with a live conductor (this does not have to be considered in normal circumstances)

Very few people are killed in normal circumstances.