Connecting Power to a DC-Powered MX2020 Router with Power Distribution Modules (-48 V)
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
You connect DC power to the router by attaching power cables from the external DC power sources to the terminal studs on the PDM faceplates. You must provide the power cables (the cable lugs are not supplied with the router).
To connect the DC source power cables to the router:
- 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.
If the PSMs are installed in the router, make sure the power switches on all PSMs are turned to the off (
- Move the DC circuit
feed switch on the PDM faceplate to match the current rating amperage—
60 A, or
80 Afor each feed.
The switch position applies to all inputs of this PDM. Selecting the 60 A position may reduce power output capacity available from each PSM.
The type of feed that you use on the DC PDM (60 A or 80 A) or DC PDM depends on the distribution scheme and distribution equipment. With a 60 A feed, the maximum power supply output power is limited to 2100 W while the maximum power supply input power is limited to 2400 W. With an 80 A feed, the maximum power supply output is limited to 2500 W while maximum power supply input power is limited to 2800 W. The system power management software calculates the available and used power based on DIP switch positions in the PDM.
- Loosen the captive screws on the plastic cable restraint
on the lower edge of the power faceplate. The cable restraint is set
on hinges that hold the cover in place during cable installation.
You can remove the plastic cover for DC power cable installation by bending the plastic cable restraint cover until the two plastic pins on both sides of the housing unhinge.
- Verify that the DC power cables are correctly labeled
before making connections to the PDM. 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
RTNDC cables to chassis ground:
The cable with very large resistance (indicating an open circuit) to chassis ground is
The cable with very low resistance (indicating a closed circuit) to chassis ground is
You must ensure that power connections maintain the proper polarity. The power source cables might be labeled
(-)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 DC PDM.
- Remove the cover protecting the terminal studs on the faceplate.
- Remove the nut and washers from each of 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 the split washer, and 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
Secure each negative (–) DC source power cable lug to the
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 the nut is improperly threaded may result in damage to the terminal stud.
The maximum torque rating of the terminal studs on the DC PDM is 25 lb-in. (33.89 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 PDM terminal studs.
The DC PDMs in slots
PDM3/Input1can be powered by dedicated power feeds derived from feed
A, or feed
B. This configuration provides the commonly deployed
A/Bfeed redundancy for the system to balance the power draw.
- Close the plastic cable restraint cover over the terminal studs on the faceplate.
- Route the positive and negative DC power cables through the left and right sides of the cable restraint.
- Tighten the cable restraint captive screw to hold the
power cables in place.
The maximum torque rating of the cable restraint screws on the DC PDM is 25 lb-in. (33.89 Nm). Use only a torque-controlled screw driver to tighten screws on the DC PDM cable restraint.
- 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.
- Repeat Steps 3 through 12 for the remaining PDMs.