AC Current Switches

AC current switches provide a trip relay output when a certain predefined current level is exceeded or dropped down below a threshold. The typical application revolves around alarm signaling. AC current switches are available with solid or split core designs. When selecting a current switch, you will need to match the current range being monitored is within the range of the switch and the switch output can handle the load that is connected to the switch output. Powering the switch is usually not a concern as most all switches are self powered. If your system has current swings that settle quickly and are not alarm conditions, select a switch with a time delay. The time delay feature will ignore the alarm condition for a predefined period of time. If the alarm condition persists after the time delay expires the switch will activate. Most switches are available with an NO or NC designation. Simply put a NO (Normally Open) switch acts as an open or broken circuit under normal operating conditions. An NC (Normally Closed) switch will operate in a closed or continuous circuit until the alarm is tripped, at which point the NC switch will flip to an open circuit. As simple example of an alarm circuit with a normally open current switch could be a switch monitoring the run current on a motor. The output of the switch could be connected to a horn wired in series with its AC power source. Under normal operation the switch would operate open thus denying the AC power to the horn, as a result the horn would not sound. All is good and quiet. Now imagine the motor was being put under a heavier than normal load, it would draw more current to continue its rated operating capacity but at a higher current. If this current draw is more than the set point of the current switch the switch would flip from normally open to a closed state. Now the output AC power circuit to the horn will be a closed circuit, the horn will be energized and a loud sound will signal plant personnel that the motor is under abnormal stress.