I have just tried to extend an existing ring circuit to add a new socket, but have run into problems. I located the ring cable, cut it and installed new cable to the new outlet and back again using 30A junction boxes. However as soon as i tried to run something from the new outlet the RCD at the consumer unit tripped. Assuming I had introduced a fault somewhere I then disconnected the new cable and connected the two junction boxes to restore the original loop, minus my new addition. However, although the circuit functions it still trips the RCD very easily if anything of reasonable power (eg. vacuum cleaner) is started. Before my meddling this circuit was very stable, never had any problems. It is not overloaded, only a PC and TV most of the time. Its as if the headroom has been reduced significantly, but I don't understand how that can be. If there's an earth fault or something on the circuit wouldn't the RCD refuse to re-set ? Grateful if someone could point me in the right direction on how to troubleshoot this.