Earthing Question

[bright_spark]

Could some one please tell me in the event of an earth fault, what will operate and disconnect the supply of an istallation with earthed equipotential bonding and automatic disconnection where the circuit is not protected by and RCD?

Many thanks.

[professorgbr]

Hello
In the event of a short circuit to earth the protective device for that circuit should operate or the electricity companies protective device if the fault is at the origin of the installation
But in the event of an earth fault were the earth is not present the installation and its users are at risk
an RCD is meant to provide supplementry protection against earth faults which can an electric shock risk

[solo3uk]

In the event of an earth fault (phase to earth) or overload (phase to neutral) a fuse, (either rewirable or cartridge), or a circuit breaker, will operate in the conditions you describe.

An RCD is a general term for a Residual Current Device and it is either a RCCB (Residual Current Circuit Breaker), which will only operate when there is an earth fault, but not under overload, or an RCCBO, which is a Residual Current Device with Overload protection, so it will operate under an earth or overload fault.

An RCCB needs another device, either fuse or CB to protect it against overload

The difference between a fuse or CB and an RCD is in the way they break. The Fuse and CB break by passing the earth fault or overload current through that device, whereas the RCD works by sensing the difference in current flowing through the phase an neutral, and therefore it needs much less current, therefore more safe as far as voltage on the exposed or extraneous conductive parts, and is more sensitive.