Slightly unusual mains cold water supply

[skenk]

Are they not a bit tricky to fit, those lead-loc's?, how do you do 'em?

 

[Paul_C]

I would rather have confused technicians than a floating neutral being the only earth for an installation.

Ditto. But then given the number of parallel earth paths via bonded pipework, structural metal etc. which will be present on the neutral anyway, I can't see how it could add any confusion.

I would certainly want some sort of earth electrode of my own on the neutral of a TN-C-S system, be it a made electrode sunk specifically for the purpose or by way of a bonded metallic supply pipe (under my control so that I know it cannot be replaced with plastic without my knowledge). The lower the impedance to earth which can be maintained on my side of the installation, the more it will keep the voltage down in the event of the supplier's neutral going bad.

A pipe is a pipe and a rod is a rod. That is written in the regs. do not question them, it will confuse people if they have to think about it.

And thinking back on the discussion, I have a feeling that was the problem - Not enough thinking about what would be happening at the basic electrical level, and too much blind reliance on having been taught that "Earth rod means TT, connection to supplier's neutral means TN-C-S" and never shall the twain meet.

Or maybe the electrons just aren't clever enough to know that they're supposed to flow through a purposely driven earth rod but not through a piece of pipe which happens to be in contact with the same earth?

 

[westie101]

Not enough thinking about what would be happening at the basic electrical level,

This is my point there is too much the book/computer says and not enough understanding of why!


PME - A cautionary tale

A colleague attended an interesting fault last week.
We got reports of shocks from water pipes. On site were 3 houses and a derelict barn fed from a 25kVA transformer via modern XLPE underground cables.
A plumber had been replacing the plumbing in one of the houses, plastic water service, bonding near the stop tap, but as he tried to connect the existing (bonded) pipes to the new (unbonded) ones the shocks and sparks were occurring, there was a measured 40V between them!
(think of this we have some copper pipes within a building that have picked up a connection to an earth just by being there)

Investigation finally found there was a fault in the derelict barn that protection was not clearing, we don't know what or why as it was too dangerous to enter so we disconnected the service and the problem disappeared.
The customers in the other two houses had not even been aware there was a problem as the bonding in those houses was correct.

 

[1john]

Are they not a bit tricky to fit, those lead-loc's?, how do you do 'em?

Very much like a compression fitting but on the lead side there is a kind of split barbed olive to bite into the lead and a rubber which compresses to make a good seal. Very easy to fit.

 

[bernardgreen]

I would certainly want some sort of earth electrode of my own on the neutral of a TN-C-S system, be it a made electrode sunk specifically for the purpose

Mine is a stainless steel rod driven into the bank of a stream and extends several feet below the permanent water table. It has been known to carry an amp or three during a severe phase unbalance in the local network after a cable fault.