Juniper SRX550, Hardware Manual

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7. Verify that the DC power cables are correctly labeled before making connections to the power supply.
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 will be –48V.
•
The cable with very low resistance (indicating a closed circuit) to chassis ground will be 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 terminals on the power supply.
8. Connect DC power cables to the A+ and A- terminals:
a. Remove the screws and square washers from the A+ and A- terminals. Use a Phillips (+) screwdriver,
number 2. The square washers are permanently attached to the screws.
b. Secure each power cable lug to the appropriate terminal with a screw. Apply between 23 lb-in.
(2.6 Nm) and 25 lb-in. (2.8 Nm) of torque to each screw.
•
Secure the positive (+) DC source power cable lug to the A+ (return) terminal.
•
Secure the negative (–) DC source power cable lug to the A- (input) terminal.
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