The RMP121D is a discontinued reverse power relay with measurement voltage of 110 VAC and power rating of 537W. It operates on 110 VAC supply with 1W3 coupling, featuring module specifications of 63.3V and 3A. The device has a scale setting of 0.94 with inverse time characteristic, capable of detecting reverse power in the range of 0-25% with 0-20S response time.