Digital current relay for three-phase AC systems (5 A secondary CTs)


The CMD421 monitors for overcurrent and/or undercurrent in three-phase AC systems. Current is measured as true RMS values. Values are shown in real-time on the device's LCD display. The current on each phase may be displayed independently by pressing the UP and DOWN buttons on the device. Each alarm type can be independently activated or deactivated based on the system requirements. Three separate time delays (startup, alarm response, and delay on release) allow the CMD421 to be tailored to specific applications. Two SPDT alarm contacts may be assigned any combination of alarms.

Measurements are taken via external current transformers, one per phase. Alarm values are entered based on the secondary of the current transformer (0 - 5 A). Once the ratio is entered into the device, values shown on the display will be based on the primary of the current transformer - no mental calculations required. Ratios up to 2000:5 may be used with the device.

The CMD421 uses x:5 type current transformers (5 A secondary). For use with current transformers with a 1 A secondary, see the CMD420.

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