Tncs And Metal Shed

[m4tty]

Hi,

My brothers asked me to run some power to his metal shed on concrete base ten meters from house.

25m run swa to board. Question is his supply is tncs and I would normally earth the swa house end and leave in connector block other end and TT the shed. But this time he's just having the swa terminated into fcu for light and was going to carry on radial to few more sockets from supply side of fcu. Protected by 20a mcb in house.

Just wondered if you would run earth rod to fcu earth to earth the shed sockets and lights, doesn't seem right to me. Or would you put a small fuseboard in shed and connect earth rod.

Hope you can understand the above, having a bad day kids driving me mental ... Wish I was working

Any thoughts cheers

 

[Sidewinder]

A bit confusing mate!

However, does it "NEED" to be TT?

If it does stick a cheap garage unit in & TT.

Better all round, in fact, regardless of supply, cheap garage unit anyway TBH.

Needs an RCD regardless, also, minimise inconvenience, it's a small shed, up front RCD, no drama.

TT you could avoid if you needed to.

 

[steptoe]

deffo needs a rod one way or t'other,

do you want to make the whole installation PME or just TT the shed?

Id agree with sidey re the CU,

a small garage unit isnt going to be much more expensive than a metal clad fused spur either, plus you have your RCD and resetable MCBs rather than a blown fuse.

 

[ProDave]

It's always struck me as strange that we must TT a caravan (tin box on wheels or in the case of a static, tin box on a pile of bricks) but a tin shed sitting on the concrete is not specified what method we use.

 

[Sharpend]

The metal shed would need bonding, therefore 10mm earth out to shed if left on tncs?

 

[steptoe]

The metal shed would need bonding, therefore 10mm earth out to shed if left on tncs?

not necessarily, maybe,???  :|

 

[m4tty]

not necessarily, maybe,???  :|

If I stick a small garage board in would it be ok metalclad on TT for ease of terminating swa neatly ?

 

[Andy™]

The metal shed would need bonding, therefore 10mm earth out to shed if left on tncs?

depends if its extraneous or not

 

[Robin Spark]

If I stick a small garage board in would it be ok metalclad on TT for ease of terminating swa neatly ?

If I stick a small garage board in would it be ok metalclad on TT for ease of terminating swa neatly ?

Matty you'll need upfront 100ma rcd protection before a metal clad cu if your making the shed installation tt.

Instead Just use plastic/pvc adaptaple box before cu to make off the swa then use insulated cu for tt install.

Therefore this would be cheaper option

 

[Robin Spark]

Sorry ivmeant to say 100ma time delay rcd before shed cu If metal an tt as youll still need 30ma rcd on sockets.

Seems a bit pointless to me.

 

[Evans Electric]

We must get more questions on this than anything else and I think one cause of this is the difficulty in finding any "official " guidance  on the subject.

Nothing in the OSG that I could see for a start.

Not many Sparks are experienced in taking PME outside the zone .  

I raised this with the scam assessor years ago , "exporting earth "..........  never heard of it !!

The first problem I came across with PME   was it couldn't be used for petrol stations .      On of the problems on them was that the fuel tanks had a better earth potential than the network terminal and sparking between the two "earths " could occur.

Had it on a new build hospital once .....the  days of earthed metal cased portable drills .... if you tried to drill any steelwork , a spark would jump off the end of the drill bit onto a stanchion etc.  .  Bit un nerving sometimes.  

 

[steptoe]

stick a 100mA TD upfront of the entire install,

that way if you are using SP RCBOs you have at least got some sort of DP protection.

 

[SLIPSHOD & SLAPDASH]

Recording studios don't like PME/TNCS either. We are doing one at the moment, its TNS & they are still running all the mixing desks, recording equipment etc through UPS's and some other sort of 'cleaner'. We have done the installation as normal and they are doing the Ups//cleaner line connections themselves which i am glad as i dont think it meets the regs. I think even the cpc's are isolated from earth through a transformer(so what are they doing ?)

Thought of the day.

If a metal sheds electrics  are  connected to a TT supply does the Rcd have to be outside the shed ?

 

[Robin Spark]

Recording studios don't like PME/TNCS either. We are doing one at the moment, its TNS & they are still running all the mixing desks, recording equipment etc through UPS's and some other sort of 'cleaner'. We have done the installation as normal and they are doing the Ups//cleaner line connections themselves which i am glad as i dont think it meets the regs. I think even the cpc's are isolated from earth through a transformer(so what are they doing ?)

Thought of the day.

If a metal sheds electrics  are  connected to a TT supply does the Rcd have to be outside the shed ?

Hi Slips

wouldnt that only apply if the supply cable (assuming its swa and the armour is connected to earth from the supply end) from the main CU to the shed was already TT at the origin?

Can I add another thought of the day?

I have been thinking about any associated risks of having simultaneously accessible class 1 fittings or equipment from 2 different earthing systems?

 

[pewter]

Recording studios don't like PME/TNCS either. We are doing one at the moment, its TNS & they are still running all the mixing desks, recording equipment etc through UPS's and some other sort of 'cleaner'. We have done the installation as normal and they are doing the Ups//cleaner line connections themselves which i am glad as i dont think it meets the regs. I think even the cpc's are isolated from earth through a transformer(so what are they doing ?)

Thought of the day.

If a metal sheds electrics  are  connected to a TT supply does the Rcd have to be outside the shed ?

Just like Russ wassis face recommends .