The ABB 2CSJ202001R0001 is an RD3M-48 electronic residual current relay from the RD3 series. It provides residual current protection and earth-fault monitoring, and works with the whole ABB S200 miniature circuit breaker range and with Tmax moulded-case breakers up to T5, which is why it is normally specified for industrial boards rather than for final domestic circuits. It is a Type A device, so it detects sinusoidal AC and pulsating DC residual currents. Sensitivity and tripping delay are both set on the device, which is what lets one part number cover a range of installations and lets discrimination be arranged with the devices downstream. Supply voltage is 12 … 48 V AC/DC. The M version adds a pre-alarm threshold at 60 % of the set trip value and a frequency filter. The pre-alarm is the point of the device: it reports insulation that is deteriorating before the leakage is large enough to trip, so the fault can be found during planned maintenance rather than during an unplanned outage. The frequency filter suppresses the high-frequency leakage that variable-speed drives inject, which is a common cause of unexplained tripping on drive-fed circuits. Reset is manual. Supplied by cBallast on quote-to-invoice terms; lead time and freight are quoted per RFQ against the destination Incoterm.