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Morning all.

I'm after some suggestions please - I'm at the very early stages of a new build for a customer and just planning ahead for getting cables in the ground before the foundations go down.

There's a new PME supply cut-out which has been brought into a (very small) shed, and the plan is to run a cable underground for about 10 metres across to the C/U in the new house.

I'm thinking that I will put a Type S 100mA RCD in a small (metal) enclosure in the shed, and then run cables buried direct in the ground. Although, if it makes life easier, the client is happy to run a length of soil pipe or something similar to run cables inside.

So,
Do I run a length of SWA 25mm 2-core and also a length of 16mm earth, or is it going to be easier to run some SWA 3-core 25mm?

I'm concerned about working space for terminations inside the small enclosure at the supply end, so I was thinking that using the 2-core would allow me to run the earth straight to the MET rather than attempting to terminate a 25mm earth inside the enclosure which will probably only have 16mm holes in the earth bar.

Or, could I even just run some 25mm tails inside the soil pipe (or does it have to be armoured because it's buried?)

Does that make sense? Have I missed anything obvious? Would I also need to put in a 80A switch fuse at the supply end or am I covered by having the RCD?

If I go with the 2-core and separate earth, is the earth okay direct in the ground or does it need to go inside some conduit?

Sorry, just realised that's quite a few questions, but hopefully that all makes sense!
Thanks for your input and advice.
 
opefully that all makes sense!
Thanks for your input and advice.
Do I run a length of SWA 25mm 2-core and also a length of 16mm earth, or is it going to be easier to run some SWA 3-core 25mm? use 3 core. if you fit a 80A sw/fuse, 16mm 3 core will be adequate.

I'm concerned about working space for terminations inside the small enclosure at the supply end, so I was thinking that using the 2-core would allow me to run the earth straight to the MET rather than attempting to terminate a 25mm earth inside the enclosure which will probably only have 16mm holes in the earth bar.install a metal (galv.) adaptable box under your Switch/Fuse. joint the earthing conductor to 16mm., and carry the L & N tails into the Sw/Fuse.

Or, could I even just run some 25mm tails inside the soil pipe (or does it have to be armoured because it's buried?) you could do, but SWA is preferable.

Does that make sense? Have I missed anything obvious? Would I also need to put in a 80A switch fuse at the supply end or am I covered by having the RCD? a switch/fuse is essential to protect the feed cable

If I go with the 2-core and separate earth, is the earth okay direct in the ground or does it need to go inside some conduit? non-starter.

Sorry, just realised that's quite a few questions, but h
  • Suggestions for best way to wire underground supply please {filename} | ElectriciansForums.net
  • Suggestions for best way to wire underground supply please {filename} | ElectriciansForums.net
  • Suggestions for best way to wire underground supply please {filename} | ElectriciansForums.net
  • Suggestions for best way to wire underground supply please {filename} | ElectriciansForums.net
  • Suggestions for best way to wire underground supply please {filename} | ElectriciansForums.net
  • Suggestions for best way to wire underground supply please {filename} | ElectriciansForums.net
  • Suggestions for best way to wire underground supply please {filename} | ElectriciansForums.net
  • Suggestions for best way to wire underground supply please {filename} | ElectriciansForums.net
  • Suggestions for best way to wire underground supply please {filename} | ElectriciansForums.net
  • Suggestions for best way to wire underground supply please {filename} | ElectriciansForums.net
  • Suggestions for best way to wire underground supply please {filename} | ElectriciansForums.net
  • Suggestions for best way to wire underground supply please {filename} | ElectriciansForums.net
  • Suggestions for best way to wire underground supply please {filename} | ElectriciansForums.net
  • Suggestions for best way to wire underground supply please {filename} | ElectriciansForums.net
 
in case he used T/E for the underground feeder. :D:D:D
Also, before it reaches the new C/U I suspect that the route the cables are taking will probably mean that they're going to be buried in the fabric of the building at points, hence RCD.
 
Cables buried in walls <50mm requires additional protection.
I've never read that where cables are buried in the floor (concrete?)that additional protection is required.
 
Just out of interest, is the supply head going to stay in the shed indefinitely? Sounds like it. What's the shed made of? What happens if the shed falls down or future owners want to move it?

Just playing devils advocate a bit and throwing a few thoughts out there.
 
Just out of interest, is the supply head going to stay in the shed indefinitely? Sounds like it. What's the shed made of? What happens if the shed falls down or future owners want to move it?

Just playing devils advocate a bit and throwing a few thoughts out there.
Good question though!
Purpose built wooden frame/corrugated roof on a concrete base, specifically to house the incoming supply. It's a permanent structure.
 
So, the general consensus is that I can fit a 80A switch fuse, no RCD, terminate some 3-core 16mm SWA into a galv box and then run the cable buried direct into the ground. At the other end, terminate into a 30mA RCD if necessary to protect cables if buried in the walls <50mm deep.
Did I miss anything?!
Thanks for all your thoughts and comments.
 
Providing the protective device gives fault protection then yes. I would personally use an installation method that avoids the supply cables being in the wall as an overall rcd will lose your division of circuits. So either install surface or used earthed containment for buried cables.
 
as it's a new build, the SWA can go direct to the CU, thus eliminating the need for RCD if cable is buried in wall/s for part of the run.
 

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