TT SWA Feed

[PBG75]

Got a project coming up where the client doesn't want the overhead supply going to his new house.

What he wants is UKPN to redirect the TT feed to a new cabinet similar to a BT green street cabinet by the road & from there via a 100A switch fuse, a SWA in a duct to the new house which is approx 90m away. 

Having a disagreement with a companion at the moment, so i need some assistance & if i'm right he owes me a pint. 

• First question: The main earth rod doesn't have to be at the UKPN supply end, closer to the CU the better ZE ?
  
• Second Question: The metal switch fuse will require earthing, can this be done by another earth rod local to the cabinet similar to a shed supply ? 
  
• Third question The SWA will also need earthing, which end will this need to be at, the CU, the fuse or both
  
• Last question: What size cable, my software keeps coming up with 50mm & i don't think it will fit the CU main switch
  

Hopefully UKPN will give him a price so high i won't have to worry.

 

[Sharpend]

I can’t imagine Ukpn allowing you to have an unearthed connection to consumers side direct from theirs? I would probably expect them to say that at this green box will be the metering equipment and then the fused switch, your Swa will be considered to be the consumer tails. Therefore the earthing arrangements will have to be at the origin of the supply. It will be down to you to provide sufficient earthing arrangement to give you a satisfactory Ze to the whole installation. 
the cable needs to suitably sized to match the supply you are having installed and the load you intend to require, although VD will be a factor. 

 

[Andy™]

youll need at earth at the supply end, along with your RCD protection as your Zs will probably be too high, it being TT.

switched fuse will require earthing by a rod at that end. you can fit additional rods in the house if you wanted

must be earthed at supply end

nowhere near enough info... if the cable doesnt fit into the switch then use a bigger switch with bigger termianals. or take a smaller cable (25mm or whatever) that will fit into an adjacent enclosure and join to larger cable there. or use reducing pins if space allows

from your questions, id say you owe him a few pints

 

[Sharpend]

I was thinking he owed us a couple of pints meself! 

 

[Andy™]

I was thinking he owed us a couple of pints meself! 

mines a pepsi

 

[Murdoch]

Wonder what the anticipated load is for this new house

 

[Sharpend]

mines a pepsi

so is mine with a hint of Jack !! 

 

[Davethsparky]

Bury a bare copper tape in the trench for an earth electrode and you should get a nice low Ra. 

Off the top of my head I'd say 50mm sounds a bit on the small side. You'll want something like a 200A switch fuse (with 100A fuse) with cable box at the supply end and either a similar size isolator or a  terminal box at the load end to reduce down to 25mm to connect to a CU. 

 

[Evans Electric]

Rest assured  UKPN  will be charging a small fortune  .       And your 90m of   incoming feed , trenched etc  won't be cheap .  

If you want a second opinion on the size we need to know the estimated load for the house.   

I'd be surprised if this went ahead .