This Residual Current Circuit Breaker, offers a comprehensive selection of devices designed to meet most residential, commercial and light industrial requirements. The range includes two pole, AC/DC fault current sensitive and time delayed model. When in the OFF position a contact gap of 4mm is present, enabling Sentry RCDs to be used as isolating switches where appropriate. Positive indication of the opening of the contacts is only given when the legend ‘OFF-O’ can be seen on the RCD dolly. The operating dolly may be locked in either the ON or OFF position without affecting the ability of the trip mechanism to operate, i.e. the RCD is ‘trip-free’. It is not possible to hold the contacts closed when a fault condition exists. All Sentry RCDs incorporate a filtering device to provide protection against transient surges in the supply to the unit, thus reducing the occurrence of unwanted tripping.