I'm planning to rework the distribution system on the farm and have a supply in a meter house near the road, some distance from the nearest farm buildings. Basically I wish to provide a 300mA time delayed RCD at the meter house with an extended time delay so that I can pick off sub-systems along the route of the 25mm SWA main (backbone) feed cables which runs down the site and have tap-off points for each building, employing "type S" 100mA time delayed RCDs at each building distribution board incomer, followed by 30mA general purpose (fast) RCD protection for socket outlets etc. on the appropriate final circuits. Normal type S RCDs disconnect in typically less than 0.2 seconds I understand. General purpose disconnect in 0.04S at 150mA leakage current. The general purpose RCDs are freely available, the normal time delayed type S 100mA units also easy to source. Where I am finding a problem is sourcing a 300mA RCD with a time delay greater than the 100mA units have, so discrimination can be assured as I don't want to take out the whole system if an earth fault occurs on one of the distribution system cables protected by the 100mA type S units. Without going into fantastically priced speciality units does anyone know of reasonably priced 300mA RCD with a delay disconnection time between 0.2 and 1 second as allowed by 411.3.2.4 and suitable for a
100A TPN service. The service is TN-C-S so I need to convert to TT, not extend the suppliers earth into the farm systems.- posted
14 years ago