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I hope that they haven't done this as it is dangerous and illegal to combine the neutral and earth in a consumers installation in the UK.
[automerge]1596117059[/automerge]
Good question, this has the potential to be a very interesting discussion.
The third core is perfectly adequate for earthing (cpc) but not for main bonding if any extraneous conductive parts are present in the outbuilding (based on the assumption that the required size of bond is 10mm)
I assume in this scenario that main bonding is not required at the shed?
Based on these assumptions that earth rod is not necessary.
What is the earth rod actually doing electrically? That depends a little on its Ra, generally its hard to get a low enough Ra that it will make a practical difference to the earthing of a PME supplied installation. You would only start to notice it affecting the Zs of the circuit, and at the origin, if the Ra was a couple of ohms or less.
If the Ra is that low then the fault current that could flow through the rod could be higher than the 4mm CPC could safely handle and it could be non-compliant.
That earth rod, in my opinion, will in itself be an extraneous part because it is introducing an earth potential into the installation. As such it would need to be connected back to the MET by 10mm copper or equivalent.
Based on that logic it is in fact making the installation worse rather than better.
As you probably know I am an advocate of earth electrodes being connected to the MET of all installations with a PME earth, I think 10mm would be the minimum acceptable conductor size for this.
Are you saying you are an advocate of earth rods on PME but only with a low enough Ra?I hope that they haven't done this as it is dangerous and illegal to combine the neutral and earth in a consumers installation in the UK.
[automerge]1596117059[/automerge]
Good question, this has the potential to be a very interesting discussion.
The third core is perfectly adequate for earthing (cpc) but not for main bonding if any extraneous conductive parts are present in the outbuilding (based on the assumption that the required size of bond is 10mm)
I assume in this scenario that main bonding is not required at the shed?
Based on these assumptions that earth rod is not necessary.
What is the earth rod actually doing electrically? That depends a little on its Ra, generally its hard to get a low enough Ra that it will make a practical difference to the earthing of a PME supplied installation. You would only start to notice it affecting the Zs of the circuit, and at the origin, if the Ra was a couple of ohms or less.
If the Ra is that low then the fault current that could flow through the rod could be higher than the 4mm CPC could safely handle and it could be non-compliant.
That earth rod, in my opinion, will in itself be an extraneous part because it is introducing an earth potential into the installation. As such it would need to be connected back to the MET by 10mm copper or equivalent.
Based on that logic it is in fact making the installation worse rather than better.
As you probably know I am an advocate of earth electrodes being connected to the MET of all installations with a PME earth, I think 10mm would be the minimum acceptable conductor size for this.
What is the actually use of this earth rod though? An Ra even of 2 ohm is only going to give a PFC of 115A which will not blow a 100A fuse or even an 80A fuse in the cut out.
A sub 1 Ra would though.
I suppose a low enough Ra of around 2 would be sufficient to trip the MCB's in the consumer unit?