MK Sentry Standard 240V RCDs
The choice of the most suitable MK Sentry RCD for a particular application should take into account the following considerations:
10mA RCDs offer a high degree of protection against electrocution in an accidental shock hazard
situation. They are of particular value in a high risk area where resistances external to the body are likely to restrict the earth fault current flowing through the body to less than 30mA and where 110V supply is being used.
30mA RCDs offer a high degree of protection in an accidental shock hazard situation and are by far the most popular sensitivity used in the United Kingdom. In a shock situation, the current flowing through the human body at 240V 50Hz could be between 80 and 240mA, depending on the resistance of the body in question. To ensure that there are no harmful physiological effects in such a situation, it is necessary for the RCD to operate within 300mS at 30mA and 40mS at 150mA. As the Sentry RCD typically operates well below these times, it clearly more than satisfies this requirement.
100mA RCDs may, in some circumstances, provide protection against electrocution in an accidental shock hazard situation. However, it is important to note that there is a likelihood that the earth fault current may be below the sensitivity of the RCD. This becomes increasingly likely if additional resistances to that of the human body are in the current path.
300mA RCDs provide protection against the risk of fire only. They do not provide protection against electrocution in an accidental shock hazard situation. A typical application would be lighting circuits where it is deemed that the risk of electric shock is small. It is important to note that a current of less than 500mA flowing in a high resistance path is sufficient to
bring metallic parts to incandescence and, potentially, initiate a fire.