History of PME Systems.

[markythesparky]

Does anyone know the history or reasoning behind PME and TN-C-S earthing? It came up today and I thought it was worth knowing.

Why was it brought in and when?

 

[Ian1981]

Cheaper to install than running a separate earthing conductor along side the supply.
As for when, I don’t know late 70s perhaps?

 

[markythesparky]

But the old cables were lead sheath? They didn’t have a separate earth conductor. The lead would have added a cost though I suppose.

Is that the only reason? Just cost?

And what the danger of a lost N, why did they think this was safe?

 

[johnduffell]

Lost n will be discovered very fast. Lost e would not be. So it makes sense to combine as long as you trust your equipotential zone and bonding.
So you could say pme was a safety improvement, a bit like putting your smoke alarms on the lighting circuit.
Has anyone got figures for death by pme Vs death by tn-s?

 

[MFS Electrical]

The lost Nuetral could go undetected forever though because of the bonding as long as the pipes that are bonded are actually extraneous in that case the installation may well be using the bonding to the gas and water pipes as a nuetral...

 

[markythesparky]

And if the pipes are not bonded, appliances and everything metal that’s connected to a CPC becomes live. That’s not an improvement. But as you say, you’d need to trust your equipotential zone.

 

[markythesparky]

So was it because of a safety issue that it was brought in and do we have any dates?

 

[johnduffell]

The lost Nuetral could go undetected forever though because of the bonding as long as the pipes that are bonded are actually extraneous

Would that not be obvious due to high resistance neutral?

And if the pipes are not bonded, appliances and everything metal that’s connected to a CPC becomes live.

as you trust your equipotential zone and bonding

Yes no bonding would be dangerous

 

[snowhead]

and do we have any dates?

The Code of Practice for D.N.O's for P.M.E appears to be dated 1975, so will have started sometime after that date,
This is G12/2 but it refers to G12/1 which would have been the start.
http://www.nienetworks.co.uk/documents/security-planning/er-g12-2.aspx

Can't find a copy of G12/1 accessable online , yet..

 

[Deleted member 26818]

Reference to PME systems were made in the 14th edition which was issued in 1966.