Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?


Maintaining the M120 Power Supplies



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


  • 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
  • Make sure that the power and grounding cables are arranged so that they do not obstruct access to other router components.

  • Routinely check the OK and the STATUS OK 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 M120 Power Supply LEDs.

  • Check the red and yellow alarm LEDs on the craft interface. Power supply failure or removal triggers an alarm that causes one or both of the LEDs to light. 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 Chassis and Interface Alarm Messages.

  • Periodically inspect the site to ensure that the grounding and power cables connected to the router are securely in place and that there is no moisture accumulating near the router. To review grounding and site wiring requirements for the router, seeDC Power Electrical Safety Guidelines for the M120 Router and Site Electrical Wiring Guidelines for Juniper Networks Devices.