RCD or NOT???

Reg Man · Sep 22, 2011

I have to run a 70mm SWA sub circuit over a distance of 70metres in a 4in duct under ground. The cable will run from the main incoming electricity boards supply (busbar after meter). I know I will need an isolator at the front but do I need an RCD also, like a 100mA time delay???
Current being drawn will be around 120A max. The install is on a farm and the supply is a 200A CT monitored single phase TNS supply.
If anyone can point me in the right direction regarding the correct chapter in the regs it would help, if its the case I need the RCD!!

Risteard · Sep 22, 2011

Special Locations: Agricultural and Horticultural Locations.

Deleted member 26818 · Sep 22, 2011

I believe the requirements for RCD protection in Agricultural/Horticultural premises are:
30mA for circuits supplying socket-outlets (32A and below), 100mA for circuits supplying socket-outlets above 32A and 300mA for all other circuits.
Obviously this is dependant upon Zs being low enough for the RCDs to operate.

nickblake · Sep 22, 2011

The SWA cable buried in ducts at the correct depth as laid out in the regs would not need RCD protection , how ever circuits from the consumer unit it supplies will depending on the installation methods and useage check out section 705 page 216 of the regs , you will need a switch fuse however to protect the cable so as not rely on the supply fuses

Deleted member 26818 · Sep 22, 2011

705.411.1 In cicuits, whatever the type of earthing system, the following disconnection devices shall be provided:
(i) In final circuits supplying socket-outlets with rated current not exceeding 32A, an RCD having the characteristics specified in Regulation 415.1.1
(ii) In final circuits supplying socket-outlets with a rated current more than 32A, an RCD with a rated residual operating current not exceeding 100mA
(iii) In all other circuits, RCDs with a rated residual operating current not exceeding 300mA.