6. Remove the clear plastic cover protecting the terminal studs on the faceplate.
7. Remove the nuts and washers from the terminal studs.
8. Secure each power cable lug to the terminal studs, first with the flat washer, then
with the nut (see Figure 106 on page 260). Apply between23 lb-in. (2.6Nm) 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 the positive (+) DC source power cable lug to the RTN (return) terminal.
b. Secure the negative (–) DC source power cable lug to the –48V (input) terminal.
CAUTION: Ensure that each powercable lug seatsflushagainst 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.
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.
NOTE: The DC power supply in PEM0 must be powered by dedicated
power feeds derived from feed A, and the DC power supply in PEM2 must
be powered by dedicated power feeds derived from feed B. This
configuration provides the commonly deployed A/B feed redundancy for
the system.
NOTE: For information about connecting to DC power sources, see “DC
PowerSupply ElectricalSpecifications for the MX240 Router” onpage143.
341Copyright © 2017, Juniper Networks, Inc.
Chapter 26: Replacing Power System Components
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