• Supported Platforms
• M120 Routers

• Related Topics
• M120 DC Power Supply Description
• Electrical Specifications for the M120 DC Power Supply
• Maintaining the M120 Power Supplies
• Removing an M120 DC Power Supply

Installing an M120 DC Power Supply

To install a DC power supply (see Figure 1):

1. Make sure that the voltage across the DC power source cable leads is 0 V and that there is no chance that the cables might become active during installation.

   Caution: You must ensure that power connections maintain the proper polarity. The power source cables might be labeled (+) and (–) to indicate their polarity. There is no standard color coding for DC power cables. The color coding used by the external DC power source at your site determines the color coding for the leads on the power cables that attach to the terminal studs on the power supply faceplate.

2. Attach an electrostatic discharge (ESD) grounding strap to your bare wrist, and connect the strap to one of the ESD points on the chassis.
3. Switch the circuit breaker on the power supply faceplate to the off position (O).
4. Using both hands, slide the power supply into the chassis until you feel resistance.
5. Firmly push the power supply into the chassis until it comes to a stop. The power supply faceplate should be flush with any adjacent power supply faceplates.
6. Tighten the captive screws on the top and bottom flanges of the power supply faceplate to secure the power supply in the chassis.
7. Remove the clear plastic cover protecting the terminal studs on the faceplate.
8. Remove the nut and washer from the terminal studs.
9. Attach the lugs on the DC source power cables to the terminal studs, making sure the cables are not touching or in the way of any router components:
   • Attach the positive (+) DC source power cable lug to the RETURN (return) terminal.
   • Attach the negative (–) DC source power cable lug to the –48V (input) terminal.

     Note: For information about connecting to DC power sources, see M120 DC Power, Connection, and Cable Specifications.

10. Secure the power cable lugs to the terminal studs, first with the flat washer, then with the nut. Apply between 12 lb-in. (1.4 Nm) and 15 lb-in. (1.7 Nm) of torque to each nut (see Figure 2).
11. Loosen the captive screw on the cable restraint on the lower edge of the power supply faceplate.
12. Connect each DC power cable to the appropriate external DC power source.

    Note: For information about connecting to external DC power sources, see M120 DC Power, Connection, and Cable Specifications.

13. Switch the power switch on the power supply faceplate to the on position (|). Verify that the status LED on the power supply faceplate blinks, then lights steadily approximately one minute after you switch on the power switch.