source (A) to one power supply and connect source (B) to the second power supply. This configuration
provides the commonly deployed A/B feed redundancy for the system.
The terminal block of the power supply has four terminals labeled V+, V+, V–, and V– for connecting
DC power source cables labeled positive (+) and negative (–). The V+ terminals are shunted internally
together, as are the V- terminals. Figure 50 on page 105shows the DC power supply faceplate of a
QFX5120-48Y switch.
CAUTION: The connection between each power source and power supply must
include a circuit breaker.
Do not connect two sources to a single power supply because doing so can potentially
cause circulating current in feed wires whenever there is any difference in the voltage
of the two sources.
a. Secure the ring lug of the positive (+) DC power source cable to the V+ terminal on the DC power
supply.
b. Secure the ring lug of the negative (–) DC power source cable to the V– terminal on the DC power
supply.
c. Tighten the screws on the power supply terminals until snug using the screwdriver. Do not
overtighten; apply between 5 in-lb (0.56 Nm) and 6 in-lb (0.68 Nm) of torque to the screws.
104
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