NOTE: The switch powers on as soon as power is provided to the power supply. There is no power switch
on the QFX5120.
To DC power to a DC-powered QFX5120-48Y or QFX5120-48T switch:
1. Wrap and fasten one end of the ESD wrist strap around your bare wrist, and connect the other end of the strap to a
site ESD point.
2. 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 low resistance (indicating a closed circuit) to chassis ground is positive (+) and will be installed
on the V+ (return) DC power input terminal.
•
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 coding for
DC power cables. The coding used by the external DC power source at your site determines the
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.
NOTE: The V+ terminals are referred to as +RTN, and the V– terminals are referred to as –48 V in DC Power
Wiring Sequence Warning and DC Power Electrical Safety Guidelines.
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.
6. Remove the screws on the terminals using the screwdriver. Save the screws.
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