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Alarm Isolation Unit

The Alarm Isolation Unit (AIU) is a 6 channel alarm isolator unit for “hot site" isolation of alarms on high voltage and medium voltage plants. The isolator is intended to be used to isolate DC alarm contacts on “hot“ equipment via field wiring with the electronic inputs of monitoring equipment (SCADA, PLC).

Potentially under fault or flashover conditions the field sensing contacts can be raised to many thousands of volts above ground potential, which would damage low voltage monitoring equipment.

The alarm isolator unit is mains powered with a nominal 50V DC feed to remote alarm contacts via field wiring. These contacts in turn activate the isolated relays in the alarm isolator. Up to six isolator relays can be fitted to the DIN rail in the unit, and easily replaced if required. The unit will operate on field wiring up to a maximum loop resistance of 1000 ohms.

  • Galvanic isolation of 15KV RMS
  • Protects SCADA interfaces from high field ESD
  • Sense loop up to 1000 ohms
  • LED loop indication
  • Up to 6 independent channels
  • Low power
  • Modular relays

Typical Alarm Isolation Unit Application



Contact Configuration: Single pole change over

Switching Current: 0.25A 

Switching Power: 5VA max

Switching Voltage: 175V max AC/DC

Contact Resistance: 100m?

Maximum Release Time: 1mS

Operating Time Typical: 0.7mS

Mechanical Life: 103 operations

Must Operate: >35V

Must Release: <10V

Coil Current: 20mA max

Isolation: 15,000 V RMS

Size W x D x H: 280 x 220 x 180

Power: 85 to 264 VRMS

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