SPD alarm contact monitoring

Some surge protection devices have a form C relay contact that reports SPD status remotely, so a monitoring system can see whether the device is still protecting. The contact wires connect through a three-terminal connector. In normal operation the audible alarm is off and the normally closed contact stays closed. Apart from this remote status signal, the device needs no operator action other than watching its display panel for status. On some models you can read the alarm status from the display or over communications. It shows either Protected or Active Alarm Replace SPD, and the display also shows how much protection remains on each phase. A red phase or neutral-ground LED, often with the audible alarm, means a significant surge event or lost protection, which indicates an exhausted surge protector that should be replaced. If every phase alarms at once, the cause can also be an extended temporary overvoltage or an SPD rated below the system voltage, so check the electrical system before fitting a replacement. If the alarm has been silenced, a red LED can still show a fault. If all LEDs and the display are off, the SPD may simply have no power, so check the system voltage at its connection. Some inverters raise their own SPD warning. For this alarm, a red indicator means replace the SPD module, and a green indicator means remove and reinstall it in its socket.

<!-- review notes

• sentence 4: support check: partial - The display menu shows the Protected/Active Alarm states and per-phase protection level, but the register passage does not list those values, and 'some models' is not stated.
• sentence 8: support check: partial - Red means replace and green means remove and reinstall in the socket, but the passage says 'DC' SPD under Warn0100 (AC SPD) and does not say 'some inverters' generally. -->