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Topic Title: pme or not
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Created On: 18 June 2013 07:38 PM
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 18 June 2013 07:38 PM
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wylexman

Posts: 68
Joined: 12 March 2011

evening all,
im in the middle of fitting a 3 phase fuseboard to a new supply in a barn to be used as a little garage workshop, theres stickers on the new supply saying its a pme system but i thought barns and commercial was tt.
ive tried phoning the local electric board but as usual dont get anywhere.
many thanks.
 18 June 2013 09:22 PM
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statter

Posts: 126
Joined: 06 February 2013

... it means the earth terminal that has been provided is a PME one. Its up to you whether you use it or not. I'd agree, normally a barn / garage would have a TT supply - just don't use the PME earth terminal and drive your own rods for TT.
 18 June 2013 09:24 PM
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prophet

Posts: 258
Joined: 09 October 2011

Think you may be thinking of not using a TN-C system in agricultural. Is it a farm and is the work you're doing confined to the barn?
 18 June 2013 09:41 PM
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wylexman

Posts: 68
Joined: 12 March 2011

its on a farm but all work is confined to inside the unit, its going to be rented out as a garage workshop
 18 June 2013 09:58 PM
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leckie

Posts: 2024
Joined: 21 November 2008

A workshop is not a farm. So why not use PME. If the PME is within the building there are no "exporting of PME" to consider. I don't see a problem on the face of it.
 18 June 2013 10:20 PM
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John Peckham

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What is the structure of the barn made of? What is the floor made of and covered with? How long is the cable run to the barn?

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John Peckham

http://www.astutetechnicalservices.co.uk/
 18 June 2013 10:27 PM
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Legh

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I'd agree, apply all normal earthing and bonding to the installation.

Although, you may have other conditions to think about such as BS EN 60079

Legh

-------------------------
Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."
 18 June 2013 10:27 PM
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leckie

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I think the op is saying the supply and pme terminal is in the barn, i.e. not a distribution circuit.
 20 June 2013 08:15 PM
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UKPN

Posts: 548
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"Ive tried phoning the local electricity board but as usual dont get anywhere"

clearly a CNE (PME) main and service, (it could be CNE main and SNE
(cable sheath) service) we have to ask the question is the building suitable for a PME connection?

can we create an equipotential zone? are there services to bond, even if
they have plastic incomers and metallic piping? is the concrete in contact with the general mass of earth? it is a barn, wood construction, so perhaps a 500mA rccd at the origin? a workshop, so operatives will be laying on the ground at times, so 30mA trips for protection?

my opinion is this project will be suitable for a PME connection with an
excellent return earth path.

Regards
 20 June 2013 08:31 PM
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OMS

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my opinion is this project will be suitable for a PME connection with an excellent return earth path.


WTF is an excellent return earth path - it's just the system neutral - with all the attendant problems that brings.

Regards

OMS

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Failure is always an option
 20 June 2013 09:08 PM
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UKPN

Posts: 548
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"with all the attendant problems that brings"

"failure is always an option"

what is this, gloom and doom week!

Regards
 20 June 2013 10:15 PM
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slittle

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If it's a steel framed building with nothing else too close and you can create a zone then you could go for it.

Let's face it all the steel in the ground is going to hold everything close to where it should be.

However, if it was my job on a remote (long way down the network) site would I use the PME terminal....... er........ nope, I'd go RCD incomer and a nice rod.

In a town centre industrial unit, yep, I'd PME it.

The difference..... you mentioned the magic word "farm" and in my book (never mind 7671, EAW and ESCQR) pme and farm doesn't land on the same page I'm afraid. Can't help it, just the Essex boy in me


Stu
 21 June 2013 08:35 AM
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broadgage

Posts: 1358
Joined: 07 August 2007

I would be inclined to TT it.

It is said to be part of a farm and even if not used for agricultural purposes at present, might well revert to full or partial agricultural use in the future.

Secondly the expected use is said to a garage, presumably for vehicle maintenance.
This to me suggests vehicles being repaired that are too large or too numerous to fit in the barn. Virtualy certain to involve the outdoor use of portable tools and lighting, outside the equipotential zone.
Probably outside lighting that even if mounted on the building can be touched by persons on the ground, and probably outdoor water taps for washing vehicles.

And as above it might be relatively remote and the suppliers combined PEN conductor more liable to theft or failure than an interconnected urban network.
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