SUPPLY CABLE TO OUT BUILDINGS

[SPARKY LEE]

hi need some advice please , i need to run a supply from a farm house to another out building.the runs about 45 m the load is 60 amps , the farm house is fed from an overhead supply,therefore TT system, my question is about cable protection ,the cable i have is 35mm concentric ,which would have to be buried ,the outbuilding again will be TT ,im a bit unsure how to protect this cable as it has no earth ,therefore using an rcd as the switch wont work, how about an rccb or rcbo as it will protect against overcurrent as well as shortcircuit current ,any ideas please as im worried that if someone hits this cable in the futre the device might not work many thanks lee

 

[plugwash]

you are using plain concentric (not split con)? you are aware that doing so is a departure from BS7671 (neutral only single insulated)?

with that out of the way your spade should hit the neutral (which is at least nominally at earth potential) before hitting the live. Thats what the recs rely on when they use the stuff underground.

 

[Lectrician]

Other than that - a 60amp load is very significant for a supply originally intended for a domestic dwelling. This type of addtional load should be put past the DNO before you commence.

DNO's usually provide TN-S when possible for farms.

I hope you can ensure that the TT arangements and main equipotential bonding is adequate before commencing work.

 

[SPARKY LEE]

my hands are up i didnt know thanks, i have the cable thats all , we used to use it on street lighting but protection was either a 1361 or bs 88, il,e buy some three core swa cheers mate

 

[SPARKY LEE]

if i can get hold of some split con can you see any problems with that ,least i can use an rcd to protect it thanks lee

 

[Lectrician]

Where will you take the feed from? After the primary RCD already installed? Or are you planning to create a an entire 'new' installation?

TT systems are a pain in the arse - It isn't simply a matter of sinking a rod in the ground....

 

[SPARKY LEE]

its an existing instalation but the original cable was inadequate ,i was going to take some tails from phase blocks after the meter in the house ,to feed the rcd .At the other end of the circuit ,the original cu in the out building is 60 amp but il'e probably put a new board in with a 40 amp rcd , if split con is ok il'e go for that thanks again for your help lee

 

[Lectrician]

You need more than just an RCD at the origin. You need overcurrent protection aswell. What ratinf RCD at the origin, and what rating at the other end?

What length of run?

Where are you getting 60amp load from, and how can you suddenly derate to 40amp? What load is there REALLY?