Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?


Maintaining the T320 Power Supplies



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


On a regular basis:

  • To check the status of the power supplies, issue the show chassis environment pem command. The output is similar to the following:

    user@host> show chassis environment pem
  • Check that the voltages in each load zone are equal.


    The current sharing between PEMs relies on equal voltages at the input terminals of the PEMs. The T320 Internet Router system power is divided into two load zones. (INPUT 0 of PEM0 should be matched with INPUT 0 of PEM1; INPUT 1 of PEM0 should be matched with INPUT 1 of PEM1) Therefore, those two PEMs voltages 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 T320 Power System Electrical Specifications . See Typical DC Source Cabling to the Router for a typical DC source cabling arrangement.

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

  • Routinely check the LEDs on the power supply faceplates. If the CB ON LEDs are lit, the power supplies are functioning normally. For more information about the power supply LEDs, see T320 Power System Description.

  • Check the red and yellow alarm LEDs and the LCD 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 LCD. You can display the associated error messages by issuing the CLI command:

    user@host> show chassis alarms
  • 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 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, see T320 Chassis Grounding Cable and Lug Specifications and Site Electrical Wiring Guidelines for Juniper Networks Devices.

  • Regularly inspect the air filter on each power supply for dust and debris, and replace the filter element every 6 months. To replace a power supply filter element:

    1. Grasp the filter cover on the power supply faceplate and pull it straight off the power supply.
    2. Remove the filter element.
    3. Install a new filter element.
    4. Press the filter cover straight onto the power supply faceplate until all four sides click into place.