exporting earth again!!!

Talk Electrician Forum

Help Support Talk Electrician Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

scrag

Member
Joined
Apr 23, 2009
Messages
51
Reaction score
0
Gotta quote an outbuilding to be used as a office on a farm. The supply is from a 3ph DB with PME supply in barn. Sub main 60metres. Not aggrecultual and live stock not in this area so tracktor will excavate. No Probs!!

Do I 2core and TT the outbuilding or 3 core and export the PME. What about RCD protection to the SWA sub main. Seems to be a lot of confusion and would very much appreciate feedback as qoute is urgent. :eek:

 
what is the facination with TTing things? Ive noticed everyone loves it. how comes?? :)

 
Have you both read the huge exported earth threads for a start?

The gist is if there is a fault and your outbuilding has a lower resistance to earth than the PME supplied then all your fault current goes down the SWA to the outbuilding, and worse case scenario all your neighbours fault current too. Could be many 100's of amps - worse case. The earth out to the outbuilding then melts.

With a nice earth rod you have your own earth - nowt is shared etc. Much more reliable.

:D

Them that are real electricians can tell us more.

 
Great. Yeah. TT the way to go. So why have DNO's gone down PME path???

 
I seem to be getting to grips with this and appreciate feedback. It makes sence. But why do suppliers prefer PME. Is it the cost of cable or somthin else??

 
Great. Yeah. TT the way to go. So why have DNO's gone down PME path???
I have no idea? Cheap?

Why did we chose VHS over the superior Betamax?

By reading threads on here TT seems to scare some of the newbies as they don't seem to have done as much on it as PME. TT seems simple to me.

Now I realise the benefits I wish I'd not let the sparky who changed my CU change us over from TT to PME :(

 
Not a proper farm. It does work but its more of a day out for the family farm with shops and restaurent

 
Im back. Just let the dog out and topped up my glass. I would say NO it is not a farm now. Where would I earth the armour at. The PME end or the TT end. And what about RCD protection to the said cable.

 
Im back. Just let the dog out and topped up my glass. I would say NO it is not a farm now. Where would I earth the armour at. The PME end or the TT end. And what about RCD protection to the said cable.
AFAIK SWA needs no additional protection.

Earth the SWA at CU and isolate at the outbuilding.

 
Fanx all. Have a look in every now and then when I have time. Great site . Keep up the good work. Rules and regulations are for the blind obedience of fools and the guidence of wise men.

 
Have you both read the huge exported earth threads for a start?The gist is if there is a fault and your outbuilding has a lower resistance to earth than the PME supplied then all your fault current goes down the SWA to the outbuilding, and worse case scenario all your neighbours fault current too. Could be many 100's of amps - worse case. The earth out to the outbuilding then melts.

With a nice earth rod you have your own earth - nowt is shared etc. Much more reliable.

:D

Them that are real electricians can tell us more.
Hurray a short version of some very long threads Applaud SmileyApplaud SmileyApplaud SmileyApplaud Smiley

 
I understand what you are saying about this situation and TT and agree. However I am transporting the earth to domestic outbuildings, garages and the like, as I have seen too many rods not connected, for various reasons. If the earth is disconnected on PME systems nowt works as the neutral has also gone.

 
That`s all well & good; but it DOES create an isuue with the earth conductor carrying vast amount of current; which is why there is a specific reg. for TT`ing outbuildings.

You don`t HAVE to agree with or follow the regs, as long as you can prove that YOUR method was at least as safe. Exporting PME earth is not safe. FACT!

KME

 
And a missing rod connection is safe? There is an allowance in the regs for exporting earths be they TT or TNCS.

 
Top