Discuss PME systems and sub mains? in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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Staffie

Was working on an installation a few weeks ago (PME domestic) which had a sub to a garage which in turn had another sub which supplied a c/u in a shed about 20 meters down the garden.

Got talking to mate of mine on Saturday who said that both the subs should be protected by an an individual earth electrode?

This got me thinking that I'm sure I did read not so long ago, can't remember where, that the means of earthing on a PME should not be taken out of the equipotential zone, exactly what my mate had said?!

He didn't seem to know why, we both stood in the middle Morrison's both somewhat confused?(nothing new there)

I can only assume that this has something to do with the declared Ze only being applicable at the customers intake only?

Advice appreciated!

;)
 
When you take a supply to a shed, garage or similar out building you must only export the phase and neutral, not the earth. The earth at the new installation EG garage must use an earth rod. If you did export the earth to the garage and you step out of the garage holding onto part of the earthed metal-work, there is the potential to get a belt to earth. This is because there may be a potential difference between earth at the house and earth at the garage earth! Sad but true..
 
When you take a supply to a shed, garage or similar out building you must only export the phase and neutral, not the earth. The earth at the new installation EG garage must use an earth rod. If you did export the earth to the garage and you step out of the garage holding onto part of the earthed metal-work, there is the potential to get a belt to earth. This is because there may be a potential difference between earth at the house and earth at the garage earth! Sad but true..


Thanks mate, that makes sense! I must admit, I've never stuck one in and the spark who did the install on this particular job hasn't either!

So, if the garage was part of the fabric of the dwellings, I take it you may export the earth with the P&N?

;)
 
Thanks mate, that makes sense! I must admit, I've never stuck one in and the spark who did the install on this particular job hasn't either!

So, if the garage was part of the fabric of the dwellings, I take it you may export the earth with the P&N?

;)

yes you can export the earth, because its part of the eqipotential zone.:)
otherwise, if its disengaged from the dwelling, convert to a TT system.:(
 
Had a chat with niceic not long back regading exporting the earth on a PME system. They never use to allow it, but after a meeting with themselves and the IEE they now say its allowed.
 
Had a chat with niceic not long back regading exporting the earth on a PME system. They never use to allow it, but after a meeting with themselves and the IEE they now say its allowed.

Can that be found in writing anywhere? The inspector that may go to one of our jobs may never have been informed, argue with you and say to put right with an earth rod, as he knows best....
 
Hi.

Hi.

A PME system can be exported provided that the either of the following 2 conditions are met

1. There are no extraneous conductive parts within the outbuilding i.e steel frame, water service, gas service etc.

2. If there are conductive parts, then the equipotential zone needs to be extended to the outbuilding via main equipotential bonding conductors sized accordingly i.e a minimum of 10mm2 for each service back to the MET within the house, unless the sub-main is greater than 10mm2 itself.


Personally if there are conductive parts within the outbuilding then I always TT regardless of sub-main size.

Hope this helps.
 

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