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Maintaining the M320 Power Supplies



For optimum router performance, verify the condition of the power supplies.


On a regular basis:

  • The power supplies require an unobstructed airflow at both the front and rear of the chassis. Periodically check the site to ensure that both the air intake at the bottom front of the chassis and the exhaust from the power supply faceplates are unobstructed.

  • Periodically inspect the site to ensure that the grounding cable, DC power cables, and AC power cords connected to the router are securely in place and that no moisture is accumulating near the router. To review grounding and site wiring requirements for the router, see M320 Chassis Grounding Cable and Lug Specifications and M320 General Electrical Safety Guidelines and Electrical Codes.

  • Make sure that the DC power cables or AC power cords are arranged so that they do not obstruct access to other router components.

  • Check the status of the power supplies by issuing the show chassis environment pem command. The output is similar to the following:

    user@host> show chassis environment pem

    Isolated DC power supplies share current over the full input operating voltage range.

    The current sharing between nonisolated power supplies relies on equal voltages at the power supply input terminals. The M320 system power is divided into two load zones. One load zone consists of PEM0 and PEM2, and the other load zone consists of PEM1 and PEM3. For nonisolated power supplies, load sharing occurs only between the power supplies of each load zone (PEM0 and PEM2 or PEM1 and PEM3). Therefore, the voltages for each nonisolated power supply in a load zone should be equal for current sharing. However, if the voltages do not match, the router operates normally as long as the DC input voltages are within the operating range provided in M320 DC Power Electrical Specifications. See M320 DC Power Cable Specifications for a typical DC source cabling arrangement.

  • Routinely check the OUTPUT OK and the POWER OK status LEDs on the power supply faceplates and the craft interface. If these output status LEDs are lit, the power supplies are functioning normally. For more information about the power supply LEDs, see M320 Power System Description.

  • Check the red and yellow alarm LEDs and the LED display on the craft interface. Power supply failure or removal triggers an alarm that causes one or both of the LEDs to light and an error message to appear on the LED display. You can display the associated error messages by issuing the following CLI command:

    user@host> show chassis alarms

    For a list of possible alarm messages, see M320 Chassis and Interface Alarm Messages.