RCD's Residual Current Device Offers Protection against Electric Shock
Sentry 4 pole RCDs may be used to provide earth fault protection on 3 phase, 3 wire systems, as the current balance mechanism does not require a neutral to be connected in order to operate effectively.
Sentry RCDs must never be used as the sole method of direct contact protection, but are invaluable in providing supplementary protection in high risk environments where damage may occur.
However Sentry 4 pole RCDs do, ideally, require a neutral conductor to be provided on the supply side of the RCD in order to ensure that the test circuit operates satisfactorily.
Where connection of a neutral supply is not possible, then an alternative method of ensuring that the test button is operational is to fit a suitably rated resistor between the load side neutral pole and a phase pole not associated with the normal test button operation.