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

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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!!
 
any services, e.g.water in the cabin? and i'd put the RCD in the cabin, not in the house CU.
 
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well, if the whole place was TT, you'd be exceptional if you could make the garage TNC-S. :ack2:
 
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..........
 
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If it's only 2m or so from the house (granted that the cable run will be a bit longer), then I can't think of any compelling reason either technically or financially why you wouldn't just extend the earth of the PME over - using either the 3 core or a separate CPC if you've something to bond (unlikely if it's a wood cabin). If you terminate the armour properly and banjo it, then you get the 'bonus cpc' as well, so you're unlikely to have a Zs problem.
 
Well.... from what you lot are saying on here, another thread, You can use a 6mm2 3-core swa tying the armour to earth at both ends, this will give you an approximation of the 10mm2 earth+bonding cable required.
However, a Log cabin without any extraneous conductive parts will not require PME bonding.
 
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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.
 
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.
 
yes there is mate and think its a sticky by lenny have allok in the stickys not sure if in general sectio not have a look about remeber reading it and having a look at the tables
 
the value of k is lower than copper when using the adiabatic. think it's about 50. but you need to know the csa of the armour. think that may be in the sticky brucelee refers to.
 
Rockingit said:
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.
Click to expand...

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.
 
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"
 
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.
 
GLENNSPARK said:
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..........
Click to expand...

tt is still common,out in the sticks..
 
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?
 
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.
 
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tony mc said:
Funny hoW exporting PME always gets alot of debate.

Here is another sticky by IQ

A good guide For 'exported PME' and
Click to expand...

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.
 
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!!
 
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
 
perfectly adequate. you can also use the armour of the SWA as your cpc.
 
maybe if they made PME illegal, then we could'nt export it....
 
MATTMOUSE said:
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
Click to expand...

Yes, .....But!! If during installation the PVC sheath is damaged, then moisture ingress to the SWA can corrode the SWA in a relatively short time, ...time depending on the chemical make up of the soil it's buried in. I would always advise on using 3 core SWA, the cost difference is minimal, and your assured of a good CPC connection to earth when all connected correctly!!! It's a no brainer in my opinion!! ...lol!!
 
Respect to you guys for the info!!!.............is there a limit on how many seperate buildings (sheds, cabins etc) that you can use from one PME source?...........i heard that if lets say you have three sheds in your garden, you can only share or use the PME source from your main property for one shed and the other two must have a TT system.
Sorry to be a Parrot and repeat myself...........We can safely say that I can supply this cabin using the swa cpc and armouring (connected to the property PME MET) as the cabins incomming earth to feed various circuits (lighting and perhaps a small panel heater)
 
MATTMOUSE said:
Respect to you guys for the info!!!.............is there a limit on how many seperate buildings (sheds, cabins etc) that you can use from one PME source?...........i heard that if lets say you have three sheds in your garden, you can only share or use the PME source from your main property for one shed and the other two must have a TT system.
Sorry to be a Parrot and repeat myself...........We can safely say that I can supply this cabin using the swa cpc and armouring (connected to the property PME MET) as the cabins incomming earth to feed various circuits (lighting and perhaps a small panel heater)
Click to expand...

Where have you heard it?...I'd try reading 7671 instead.
 
Do it properly -make it a TT system
Run SUPPLY from the house distribution board to a new small distribution board in cabin with 2.5mm SWA
New, small distribution board in cabin will require a 30ma RCD for protection
Put a rod in the ground outside the cabin connecting to the dist' board with at least 16mm earth cable.
Put your feet up.
 
ElectricAvenue said:
Do it properly -make it a TT system
Run SUPPLY from the house distribution board to a new small distribution board in cabin with 2.5mm SWA
New, small distribution board in cabin will require a 30ma RCD for protection
Put a rod in the ground outside the cabin connecting to the dist' board with at least 16mm earth cable.
Put your feet up.
Click to expand...

...Another mythology disciple.
 
where do these myths come from?? I know.....the people that make earth rods!!!!
 
ElectricAvenue said:
Do it properly -make it a TT system
Run SUPPLY from the house distribution board to a new small distribution board in cabin with 2.5mm SWA
New, small distribution board in cabin will require a 30ma RCD for protection
Put a rod in the ground outside the cabin connecting to the dist' board with at least 16mm earth cable.
Put your feet up.
Click to expand...

Tell me, ...Are you actually being serious here, you would honestly put in a TT system (and probably a p**s poor one) for this log cabin that's just 2 metres from the main house?? I suppose you would isolate and rod an outside socket outlet too!!!

Oh and please inform us all, exactly what a 16mm earth conductor is going to achieve for this TT system your proposing?? God help your PME customers is all i can say!!
 
I was waiting for E54 to reply to this one

Do it properly -make it a TT system
Run SUPPLY from the house distribution board to a new small distribution board in cabin with 2.5mm SWA
New, small distribution board in cabin will require a 30ma RCD for protection
Put a rod in the ground outside the cabin connecting to the dist' board with at least 16mm earth cable.
Put your feet up.
Click to expand...


Good god
 
the mind boggles, and after further consideration, boggles again.
 
A while ago I was asked to connect and wire a shed, and then on to another outbuilding....shed was to be used as a workshop and the outbuilding as a welding shop. About a 60m run from the intake, and I exported the PME all the way. I just can't see the justification in trying to save a few pence per metre on 1 core in a cable, even when it's a big one.
 
They walk the same streets, breathe the same air, drink the same water; but worryingly seem to live in an entirely alternative dimension.

Hmmm.....let's make a guess as to where his training came from............
 
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