Discuss Supply to garage. in the UK Electrical Forum area at ElectriciansForums.net
You are not 'exporting PME', you are simply extending an existing earthing system.
I've never ever heard anyone say they are 'exporting TNS....or TT'.
It's not a special location.
Yes absolutely right, when I posted I had in mind my general point about sheds/garages etc and completely forgot the OP's job includes a car charger.The car charger comes under Special installations (722). That's what I was getting at when asking regarding why going for TT. He may be still ok with PME still if nothing is extraneous and also that the charger meets criteria of 722.411.4.1 (iii).
If the remote building has a concrete earth floor, or conductive floor, or the building is of metal construction or metal outside skin, the shock risk is increased. It’s therefore recommended that the remote building has a TT earthing system.
When meter tails are over 3m an isolator is normally needed to satisfy the dno.
The discussion was if the new tails absolutely have to have a fused switch then why is just an isolator acceptable for every other property in the uk with meter tails over 3m.
The reason for the TT is its safer.
How would you like to explain it so we can avoid the endless circle.That's half the problem - the phrase 'exporting PME'. Can we just abolish it here and now??!!
I was referring to an article in electriI've not seen anything in the regulations, or in the rules for the application of PME preventing its use in concrete floored buildings, not have I ever heard of a DNO refusing to provide a PME connection due to a building having a concrete floor.
Yes for some metal structures they will refuse to provide a PME connection due to the increased risk.
Do you have any reasonable evidence to explain and support this, regulations, guides to the regulations, technical publications etc?
A fuse or circuit breaker is required to satisfy the DNO as they do not allow their fuse to be used to protect tails over 3m long (in most cases although some do allow 4m and some say the length must include the tails from cutout to meter)
Just an isolator is not acceptable for every other property in the UK with tails over 3m.
TT is not safer to the best of my knowledge, unless you can get a very good resistance to earth from the earth electrodes you install, then it may become equally safe.
PME provides a very low resistance earth directly back to the transformer, TT generally provides a much higher resistance path which can vary with seasonal changes and disturbance of the ground.
The last set of earth rods I installed had a combined Ra of 18 ohms, that's over 50 times the design value of a PME earthing connection for a 100A service.
I've not seen anything in the regulations, or in the rules for the application of PME preventing its use in concrete floored buildings, not have I ever heard of a DNO refusing to provide a PME connection due to a building having a concrete floor.
Yes for some metal structures they will refuse to provide a PME connection due to the increased risk.
Do you have any reasonable evidence to explain and support this, regulations, guides to the regulations, technical publications etc?
A fuse or circuit breaker is required to satisfy the DNO as they do not allow their fuse to be used to protect tails over 3m long (in most cases although some do allow 4m and some say the length must include the tails from cutout to meter)
Just an isolator is not acceptable for every other property in the UK with tails over 3m.
TT is not safer to the best of my knowledge, unless you can get a very good resistance to earth from the earth electrodes you install, then it may become equally safe.
PME provides a very low resistance earth directly back to the transformer, TT generally provides a much higher resistance path which can vary with seasonal changes and disturbance of the ground.
The last set of earth rods I installed had a combined Ra of 18 ohms, that's over 50 times the design value of a PME earthing connection for a 100A service.
I was referring to an article in electri
Exporting A PME Supply To Another Building
In this article the technical team at Stroma Certification offers expert guidance on exporting a PME supply to another building. One of the most common queries to the Stroma help desk concerns runningprofessional-electrician.com
Doesn't say it's not allowed but was referring back to this.
Probably a majority of buildings with a PME supply have a concrete floor.I'm sure a lot of us have been to, and worked on, installations which have a PME supply and a concrete floor.
I 'exported' the PME to a socket by a pond last week, never ever seen anyone TT a pond socket..
Probably a majority of buildings with a PME supply have a concrete floor.
My house does. And so does my attached garage, it's on the same PME as the house.
I do often wonder why the 'exporting' thing only seems to apply to PME??
Why dont we 'export' TT or TNS?
And why does it only apply to outbuildings? Why does the fear of PME seem only to apply to outbuildings?
I 'exported' the PME to a socket by a pond last week, never ever seen anyone TT a pond socket..
I understand the potential dangers of PME supplies, I don't need that explaining.It only applies to PME because of the of the potential risk of exposed and extraneous conductive parts rising to mains potential if the PEN conductor suffered a broken earthed neutral and the line conductor stayed intact. This cannot occur on a TN-S or a TT as they have separate conductors.
Reply to Supply to garage. in the UK Electrical Forum area at ElectriciansForums.net
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