The CM relay is designed to provide protection against unbalanced phase currents by operating to trip the circuit breaker when a fixed percentage of unbalance exits between any two phases. It will, therefore; protect motors under load when the desired sensitivity cannot be obtained by a voltage operated relay, since polyphase machines tend to maintain normal phase voltage even with one phase open, unless the machine is heavily loaded.
The CM relay is used primarily for motor protection on a three phase system. It can also be used to detect phase unbalance or open phase. Any applications requiring the detection of phase current unbalance in a polyphase system can use the CM relay.
Why ABB?
- Long product life
- Ease of application
- Reliable protection
- High-quality design