Juniper MX2020 Hardware Manual page 338

NOTE: 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.
4. 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.
NOTE: 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.
5. 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 –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:
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 DC
PDM.
6. Remove the cover protecting the terminal studs on the faceplate.
7. Remove the nut and washers from each of the terminal studs. (Use a 7/16-in. [11 mm] nut driver or
socket wrench.)
8. Secure each power cable lug to the terminal studs, first with the flat washer, then the split washer, and
then with the nut (see
You must ensure that power connections maintain the proper
Figure 142 on page 320). Apply between 23 lb-in. (2.6 Nm) and 25 lb-in. (2.8 Nm)
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