Juniper SRX 5800, Hardware Manual

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The cable with very large resistance (indicating an open circuit) to chassis ground is –48V.
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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
power supply.
6. Remove the nuts and washers from the terminal studs. (Use a 7/16-in. nut driver or socket wrench.)
7. Secure each power cable lug to the terminal studs, first with the split washer, then with the nut (see
Figure 109 on page 247 ). Apply between 23 lb-in. (2.6 Nm) and 25 lb-in. (2.8 Nm) of torque to each nut.
(Use a 7/16-in. nut 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.
The DC power supplies in slots PEM0 and PEM1 must be powered by dedicated power feeds derived
from feed A, and the DC power supplies in slots PEM2 and PEM3 must be powered by dedicated power
feeds derived from feed B. This configuration provides the commonly deployed A/B feed redundancy
for the system.
8. For standard-capacity DC power supplies, secure each DC power cable to its strain relief bracket as
follows:
a. Loosen the captive screw on the cable restraint on the lower edge of the power supply faceplate.
b. Route the positive and negative DC power cables through the left and right sides of the cable
restraint.
c. Tighten the cable restraint captive screw to hold the power cables in place.
9. Replace the clear plastic cover over the terminal studs on the faceplate.
10. Verify that the power cables are connected correctly, that they are not touching or blocking access to
services gateway components, and that they do not drape where people could trip on them.
11. Repeat Steps 3 through 10 for the remaining power supplies.
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