Juniper Networks EX8208 manual Copyright 2010, Juniper Networks, Inc

Complete Hardware Guide for EX8208 Ethernet Switches

5.Ensure that the power source circuit breaker is open so that the voltage across the DC power source cable leads is 0 V and that the cable leads do not become active while you are connecting DC power.

6.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 high resistance (indicating an open circuit) to chassis ground is negative (–) and will be installed on the –48V (input) DC power input terminal.

•The cable with very low resistance (indicating a closed circuit) to chassis ground is positive (+) and will be installed on the RTN (return) DC power input terminal.

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 DC power input terminals on each power supply.

7.Install each power cable lug on the DC power input terminal, securing it first with a locking washer, then with the nut (see Figure 69 on page 179). Apply between 29 in.-lb (3.3 Nm) and 31 in.-lb (3.5 Nm) of torque to each nut. (Use the 3/8-in. [9.5 mm] nut driver or socket wrench.)

a.Secure each positive (+) DC source power cable lug to the RTN (return) DC power input terminal.

b.Secure each negative (–) DC source power cable lug to the –48V (input) DC power input terminal.

Each power supply has two independent sets of DC power input terminals (A: –48V

A:RTN and B: – 48V B: RTN ). For feed redundancy, each power supply should be powered by dedicated power feeds derived from feed A and feed B. This configuration provides the commonly deployed A/B feed redundancy for the switch.

NOTE: If the power cord tray is installed, you can thread the DC power cables through the power cord tray.

178 Copyright © 2010, Juniper Networks, Inc.