Cisco 3800 Series Quick Start Manual - Page 22

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Cisco 3800 Series Quick Start Manual
Figure 16
Connecting to One Source Only—Source A or Source B
A-
+
A+
B+
B-
In Figure 17, source A and source B share common negative terminal connections.
Figure 17
Connecting Source A and Source B with Common Negative Terminals
Va
+
+
Vb
In Figure 18, source A and source B share common positive terminal connections. This is allowed only if Va equals Vb (within
0.25 V).
Caution
When connecting source A and source B with common positive terminals, if source A and source B voltages are
unequal by more than 0.25 V, the higher-voltage source can discharge into the lower-voltage source through the A-
and B- input terminals. Excessive discharging currents through these terminals can cause one or both of the dual
input DC power supply's internal A- or B- fuses to open, resulting in lack of redundancy or system failure. When
source A and source B are within 0.25 V, discharge current is minimal.
Note
When source A and source B are wired with common negative terminals, as in Figure 17, discharging does not occur
and there is no restriction requiring that source A and source B voltages be equal.
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+
A-
A+
B+
B-
A-
A+
B+
B-