[geoffers]

Originally Posted by retrotecchie

@geoffers NO! Water pipes may not be used for earthing .

👍 - Appreciate that, but presumably the earth bonding to incoming gas/water pipes ensures equalised PD in the system, and would provide a "last resort" return path to earth should there be a failure of the main PME somewhere?
Just trying to understand ... 🤓

[meldrewreborn]

@retrotecchie

is one permitted to have multiple earthing systems? As the occupant I have no expertise in what type of earthing I have or need - shouldn’t it be flagged up some where near the meter?

[geoffers]

Originally Posted by meldrewreborn

... As the occupant I have no expertise in what type of earthing I have or need - shouldn’t it be flagged up some where near the meter?

The majority of households these days are apparently TN-C-S (Terre-Neutral Combined, then Separated at the service head)

So if you've got the big live/neutral cable coming in at the bottom and the earth comes out at the side (being connected to the incoming neutral) you're TN-C-S, also called PEN/PME

[retrotecchie]

@geoffers

If you are on the end of the line and supplied by a pole transformer with overhead incomers, you can't have PEN/PME for obvious reasons. Your earth is a physical third cable, bonded to Neutral on the LV side of the transformer. The HV side of the transformer is earthed independently and the two earth's cannot be shared. That is known as PNB (protected Neutral Bonding). Actually the safest of all forms of earthing as you have two equipotential cables (N and E) and either are capable of handling a fault current to ground.

It also means that a Phase-Earth fault is exactly the same as a Phase-Neutral fault in the property so OCDs will always react in the fastest possible time and ELCBs or RCD/RCBO devices aren't as dependent on low earth loop impedance as other earthing methods are.

But I still use additional T-T bonding on external buildings as you should never rely on an earth return on a feeder cable if the distance from the main earthing busbar in the CU exceeds 40m.

In fact, my solar installation has three separate earth's...the main T-T earth between circuits and ground, and separate earths for the DC side.

Intriguingly, all DC equipment is positive earth, not negative earth. For the same reason that the supply voltages on copper phone networks are positive earth and the operating voltage is -48v with respect to earth.

[geoffers]

Originally Posted by retrotecchie

@geoffers

If you are on the end of the line and supplied by a pole transformer with overhead incomers, you can't have PEN/PME for obvious reasons. Your earth is a physical third cable, bonded to Neutral on the LV side of the transformer. The HV side of the transformer is earthed independently and the two earth's cannot be shared. That is known as PNB (protected Neutral Bonding). Actually the safest of all forms of earthing as you have two equipotential cables (N and E) and either are capable of handling a fault current to ground.

It also means that a Phase-Earth fault is exactly the same as a Phase-Neutral fault in the property so OCDs will always react in the fastest possible time and ELCBs or RCD/RCBO devices aren't as dependent on low earth loop impedance as other earthing methods are.

But I still use additional T-T bonding on external buildings as you should never rely on an earth return on a feeder cable if the distance from the main earthing busbar in the CU exceeds 40m.

In fact, my solar installation has three separate earth's...the main T-T earth between circuits and ground, and separate earths for the DC side.

Intriguingly, all DC equipment is positive earth, not negative earth. For the same reason that the supply voltages on copper phone networks are positive earth and the operating voltage is -48v with respect to earth.

Interesting, thanks 👍