To connect the DC source power cables to the router, follow this procedure for each
power supply:
1. 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.
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.
2. Attach an electrostatic discharge (ESD) grounding strap to your bare wrist, and connect
the strap to one of the ESD points on the chassis.
3. Switch the circuit breakers on the power supply faceplate to the OFF position (O).
4. Remove the clear plastic cover protecting the terminal studs on the faceplate.
5. Remove the nut and washer from each power terminal stud. If no washers and nuts
are already installed, they should be in the accessory box.
6. Attach the lugs on the DC source power cables to the terminal studs. Secure the cable
lugs to the terminal studs, first with the washers, then with the nuts.
a. Attach the positive (+) DC source power cable lugs to the RTN (return) terminals.
b. Attach the negative (–) DC source power cable lugs to the –48V (input) terminals.
Using a 7/16-in. (11 mm) nut driver, tighten the nuts (see Figure 100 on page 226). Apply
between 23 lb-in. (2.6 Nm) and 25 lb-in. (2.8 Nm) of torque to each nut.
CAUTION: You must use an appropriate torque-controlled tool to tighten
the nuts. Applying excessive torque damages the terminal studs and the
power supply. The absolute maximum torque that may be applied to this
nut is 45 lb-in. (5.0 Nm).
CAUTION: All inputs on the DC power supply in slot PEM0 must be
powered by dedicated power feeds derived from feed A, and all inputs on
the DC power supply in slot PEM1 must be powered by dedicated power
225Copyright © 2017, Juniper Networks, Inc.
Chapter 22: Providing Power to the T640
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