2 Core - 10mm2 PVC XLPE SWA - armour as CPC in an exported PME supply?

[Muzza80]

Hi all,
After some advice.

I'm xporting a PME supply to a timber shed/workshop with no extraneous-conductive parts. The supply will come from an aditional CU in the house with a 40amp MCB and the outbuildings will have the following circuits fed from a CU in the shed/workshop:

• 4mm2 radial socket circuit with 8 double sockets for TV, computer, phone charger, desk lamp, charging batteries of power tools and occasional use of a 1kw heater & 1500w table saw.
• 1.5mm2 lighting circuit with 8 LED downlighters, LED floodlight, 2 x LED bulkhead lights and two CCTV cameras.
• 2.5mm2 circuit for single 16amp welder socket for very occasional use of a small MIG/compressor.
• 10mm 3-core SWA 22m run to small BBQ cabin for 4 double sockets (3 x indoor / 1 outdoor) for occasional use of lower power devices.

The house to shed/workshop SWA is 2 Core - 10mm2 PVC XLPE SWA and 20M in length, and already buried.

In my situation, will the armour of the 2 Core - 10mm2 PVC XLPE SWA be sufficent CPC to export the TN-C-S earth to the outbuildings or can I only earth the armour of the cable as far as the shed/workshop and then have to TT the outbuildings?

Thanks!

 

[bernardgreen]

I would use TT at the shed / workshop if the cable is laid in the ground and not in a duct.

Reason is that any present or future damage to the sheath of the cable ( sharp stones for example ) may allow moisture into the cable and thus corrosion of the steel arnouring is possible.

 

[winston1]

Your lighting circuit does not need 1.5mm cable. 1.0mm is OK.

 

[ban-all-sheds]

I would use TT at the shed / workshop if the cable is laid in the ground and not in a duct.

I'd use 3-core, i.e. the same type of cable which I am providing between shed and BBQ cabin.

 

[ban-all-sheds]

Does anybody know what the requirements in Scotland are for a warrant are for this work?

 

[ban-all-sheds]

Hi all,
After some advice.

What are you planning to do about an Electrical Installation Certificate, and all the necessary testing

TV, computer,

Surely data cables for those?

You'll need a duct for them, so why not install 2 ducts, one for data, one for power?

2.5mm2 circuit for single 16amp welder socket for very occasional use of a small MIG/compressor.

553.1.201 Every socket-outlet for household and similar use shall be of the shuttered type and, for an AC installation, shall preferably be of a type complying with BS 1363.

And you should check to see if you need permission from your DNO for welders and compressors....

will the armour of the 2 Core - 10mm2 PVC XLPE SWA be sufficent CPC

https://www.diynot.com/wiki/Electrics:SWA-earthing

 

[bernardgreen]

I'd use 3-core, i.e. the same type of cable which I am providing between shed and BBQ cabin.

The house to shed/workshop SWA is 2 Core - 10mm2 PVC XLPE SWA and 20M in length, and already buried.

It is 2 core already laid and buried.

Also as regards to the tables you linked to ""* If the cable does not comply with table 54.7 it may still be used if it complies with the adiabatic equation. ""

 

[ban-all-sheds]

It is 2 core already laid and buried.

Missed that.

I truly cannot even begin to understand the lack of foresight and proper planning that would result in someone burying a cable and then asking if it was OK.

 

[Muzza80]

Your lighting circuit does not need 1.5mm cable. 1.0mm is OK.

Cheers, it's done anyway, was initially going to have halogen lights

Missed that.

I truly cannot even begin to understand the lack of foresight and proper planning that would result in someone burying a cable and then asking if it was OK.

Your assuming an awful lot.

I've been involved in a lengthy battle to get Scottish Power to upgrade the supply to my property.
Until just a few weeks ago there was no earth at all and the 2-core was laid many months ago at a point I'd resigned myself to having to TT the outbuildings (and possibly the property too!).
Being considerably easier to work with, and looking like there would be no need for the 3rd core I went with the 2-core.

As it transpires, SP eventually caved and ran a new supply in from the street.

So I'm now trying to work out if the armour, in this paticular case, would be sufficent for exporting the PME earth.

Can you truly begin to understand now?



Regarding adiabatic equation, can anyone offer any guidance on that? Like what I'd need to know in order to do the calculation?

Thanks!

 

[bernardgreen]

adiabatic equation

is used to calculate whether :-

(1) the CPC will melt before the over current device (fuse blows or the MCB operates) to cut the supply off.

(2) the over current device will operate in time to prevent fire and / or non reversible ( fatal ) electric shock due to fault currect.

The size of the CPC has to be large enough such that it's impedance to fault currents is low thus ensuring that the fault current is high enough to cause the over current device to operate rapidly.

https://www.tlc-direct.co.uk/Book/5.4.5.htm is a reasonable starting point that is written in a way that a DIYer may be able to understand

 

[JohnW2]

[an adiabatic equation] is used to calculate whether :- (1)...
(2) the over current device will operate in time to prevent fire and / or non reversible ( fatal ) electric shock due to fault currect.

The speed of operation of the OPD has got absolutely nothing to do with any adiabatic calculation [which is only relevant in relation to your point (1) ].

Kind Regards, John