Do I extend the PME outside to a Log Cabin style building??

[MATTMOUSE]

Please forgive me in asking this same question which normally results in an arguement......lol

I friend of mine needs to have a supply installed (a lighting circuit, a heater circuit and a socket circuit) in a SWISS style log cabin located about 2 metres away from their main home which has a PME system.
The BIG question, Can I used the PME to supply the cabin?...........I wish to use either a 6mm or 10mm 3-core swa for the supply cable, RCD protected of course.

Sorry for this post, just wanted a few thoughts on this particular installation.

A huge thanx for any thoughts guys!!

 

[ackbarthestar]

Slightly off topic - but to my mind, the amount of wire spiralling around a bit of 6mm swa must surely be more than a 4mm csa? (eq. to copper, granted). I don't know, I'm asking. If there's some table / formula for it then I don't know it.

It's not so much the csa of the steel but the comparative conductivity of the steel compared to that of copper, approximately 1:8, therefore the steel will need a csa of around 32mm2 to have the equivalent conductivity of 4mm2 copper.

 

[GLENNSPARK]

my two pence worth,
6mm 2 core swa, rcd + mcb in cabin and tt it. saves a bit of cash on cable (not much on 2m run i'll grant you, but worth it on longer/heavier runs) and no nuisance trips in house.

give up...your rod and clamp will cost more than a couple of meters of 10mm or whatever...

 

[telectrix]

give up...your rod and clamp will cost more than a couple of meters of 10mm or whatever...

not to mention the time off work with a busted hand from sledge hammering the rod in.
"sorry, mate, oops, missed it"

 

[Rockingit]

Somebody ought to plot the cost equation for using 2/3/4 core swa against 2/3/4 plus external cpc versus length, versus the adiabatic to work out what actually is the best solution.

But then, imagine the beer that could be drunk in the time taken to work it out.

 

[tony mc]

Funny hoW exporting PME always gets alot of debate.

Here is another sticky by IQ

A good guide For 'exported PME' and

 

[alarm man]

You`v got a reliable earthing arrangement with PME....why the hell would you go back to an old fashioned system (TT)? Admittedly it has its place: building sites, Moorings etc but for a perminent fixed install....not if theres TN-C-S available.....keeps cropping up on here this one..........

tt is still common,out in the sticks..

 

[Knobhead]

tt is still common,out in the sticks..

Has anyone mentioned this being out in the sticks? The OP states it’s a PME system. It’s got to the stage my blood runs cold the moment anyone mentions a shed!

 

[alarm man]

Has anyone mentioned this being out in the sticks? The OP states it’s a PME system. It’s got to the stage my blood runs cold the moment anyone mentions a shed!

i was only making an observation..and its a swiss style cabin not a shed..

 

[MATTMOUSE]

A huge thank you for the replies guys!!...........at our depot, this topic always ends up in heated debates between the work force........lol
As for the cabin there will be no services or ext' metal parts to the structure and it will be placed on a concrete foundation raised from the ground for damp proofing.
So basically, the PME can only be extended outside a property if a minimum of a 10mm copper cable is used for the earthing, if 10mm is not being used ie: 6mm 3-core swa (3rd core as incomming earth) then its best to use the TT method............is this statment a good genric rule?

 

[Rockingit]

Not quite! The general rule is that the cpc on a circuit has to be a minimum 50% csa of the line conductors - hence if it were to be 6mm twin and earth the cpc would be 4mm, etc. So, if you're using 3 x 6mm cores as L1, Ln and R2 (so to speak) then you are more than adequately covered (assuming that the size of cable is appropriate to the load, of course). The 10mm cpc comes in when talking about Equipotential Bonding, as that is the minimum now suggested by regs.

 

[ackbarthestar]

Funny hoW exporting PME always gets alot of debate.

Here is another sticky by IQ

A good guide For 'exported PME' and

Its because people do not understand it - and quite reasonably so !

There is no publicly available information to give suitable calculations regarding typical DNO supply characteristics with regard to Circulating Neutral Network currents, Network currents under fault conditions, Probability of damage and danger occurring in domestic Installations environments, probability of damage and danger occurring in industrial, special locations, licensed premises. etc.,
Chapter 54 is filled with advice, tables and formulae regarding thermal constraints for S/C conditions.
But,
The only information given to us is table 54.8. Its given to us on a need to know basis and sparkies do not need to know!
You must always remember that there are a lot of insecure To**er* out there who once get hold of a little power will use it to protect their po*ition and *tuff everybody el*e.

 

[Rockingit]

I've watched one of the NICEIC learning videos where the gruesome twosome are doing a PIR, and the shorter one does the whole nine yards of working out the adiabatic in order to justify why a 6mm main earth is more than adequate in that situation. Talk about muddying the water!!

 

[MATTMOUSE]

Thanx "Rockingit"..............So if theres no ext' metal parts that need "Bonding" in the cabin, then there's no need for the 10mm Equi bonding conductor.............could we not then rely on the 6mm swa 3rd core as the cpc supplying the cabin??............just a thought......lol

 

[Rockingit]

Yes, you could.

 

[telectrix]

perfectly adequate. you can also use the armour of the SWA as your cpc.