Juniper QFX5220, Руководство по оборудованию, Страница: 141 / 247

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The cable with very high resistance (indicating an open circuit) to chassis ground is negative (–) and
will be installed on the V– (input) 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.
3. Ensure that the input 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. The
QFX5220-32CD-D should connect the power supplies to an external DC power source, or an -0% to
+20% tolerance DC mains, supplied with a NRTL-approved circuit breaker rated at 40-A.
NOTE: The V+ terminals are referred to as +RTN, and V– terminals are referred to as –48 V in
“DC Power Wiring Sequence Warning” on page 245 and “DC Power Electrical Safety Guidelines”
on page 239 .
4. Ensure that the power supplies are fully inserted in the chassis.
5. Remove the terminal block cover. The terminal block cover is a piece of clear plastic that snaps into
place over the terminal block (see Figure 57 on page 144 ).
Figure 57: Removing Terminal Block Cover
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6. Remove the screws on the terminals using the screwdriver. Save the screws. See Figure 58 on page 145 .
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