Juniper MX2010, Hardware Manual

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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: 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 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 with the split washer,
and then with the nut (see Figure 131 on page 308 ). 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.)
a. Secure each positive (+) DC source power cable lug to the RTN (return) terminal.
b. 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 the nut is improperly threaded might result in damage to the
terminal stud.
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