MK Sentry 30mA - RCDs RCD's Residual Current Device Offers Protection against Electric Shock An RCD provides protection against earth faults occurring in equipment and reduces the effects of electric shock on human beings and thus saves lives. The MK Sentry 4 Way Consumer Unit is a white rectangular electrical panel from MK Electric designed for wall mounting. It has a height of 244mm, width of 144mm, and a depth of 116mm. This consumer unit is suitable for organising and distributing electrical connections in a business, office, or industrial setting.