Connecting Power to a DC-Powered MX240 Router
 | Caution: Do not mix AC and DC power supplies within the same router. Damage to the router might occur. |
 | Warning: Before performing DC power procedures, ensure that power is removed from the DC circuit. To ensure that all power is off, locate the circuit breaker on the panel board that services the DC circuit, switch the circuit breaker to the off position, and tape the switch handle of the circuit breaker in the off position. |
You connect DC power to the router by attaching power cables from the external DC power sources to the terminal studs on the power supply faceplates. You must provide the power cables (the cable lugs are supplied with the router). For power cable specifications, see DC Power Cable Specifications for the MX240 Router.
To connect the DC source power cables to the router for each power supply:
- Switch off the dedicated customer site circuit breakers. Ensure that the voltage across the DC power source cable leads is 0 V and that there is no chance that the cable leads might become active during installation.
- Attach an electrostatic discharge (ESD) grounding strap to your bare wrist, and connect the strap to one of the ESD points on the chassis.
- Switch the DC circuit breaker on the power supply faceplate to the off (O) position.
- Remove the clear plastic cover protecting the terminal studs on the faceplate.
- Verify that the DC power cables are correctly labeled
before making connections to the power supply. In a typical power
distribution scheme where the return is connected to chassis ground
at the battery plant, you can use a multimeter to verify the resistance
of the –48V and RTN DC cables to chassis ground:
- The cable with very large resistance (indicating an open circuit) to chassis ground is –48V.
- The cable with very low resistance (indicating a closed circuit) to chassis ground is RTN.
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 each power supply.
- Remove the nuts and washers from the terminal studs. (Use a 7/16-in. [11 mm] nut driver or socket wrench.)
- Secure each power cable lug to the terminal studs,
first with the flat washer, then with the nut (see Figure 1). Apply between 23 lb-in.
(2.6 Nm) and 25 lb-in. (2.8 Nm) of torque to each nut.
Do not overtighten the nut. (Use a 7/16-in. [11 mm] torque-controlled
driver or socket wrench.)
- Secure each positive (+) DC source power cable lug to the RTN (return) terminal.
- Secure each negative (–) DC source power cable lug to the –48V (input) terminal.
Caution: Ensure that each power cable lug seats flush against the surface of the terminal block as you are tightening the nuts. Ensure that each nut is properly threaded onto the terminal stud. The nut should be able to spin freely with your fingers when it is first placed onto the terminal stud. Applying installation torque to the nut when improperly threaded may result in damage to the terminal stud.
Caution: The maximum torque rating of the terminal studs on the DC power supply is 36 lb-in. (4.0 Nm). The terminal studs may be damaged if excessive torque is applied. Use only a torque-controlled driver or socket wrench to tighten nuts on the DC power supply terminal studs.
Note: The DC power supply in slot PEM0 must be powered by a dedicated power feed derived from feed A, and the DC power supply in slot PEM2 must be powered by a dedicated power feed derived from feed B. This configuration provides the commonly deployed A/B feed redundancy for the system.
- Replace the clear plastic cover over the terminal studs on the faceplate.
- Verify that the power cables are connected correctly, that they are not touching or blocking access to router components, and that they do not drape where people could trip on them.
- If you are installing two power supplies, repeat Steps 3 through 9 for the other power supply.
Figure 1: Connecting DC Power to the Router
