7
Cable Connection Procedures for Cisco 2800 Series Routers
OL-5787-02
Power Connections
In Figure 4, either the positive source terminal or the negative source terminal is tied to ground.
Figure 4 Connecting to One Source Only—Source A or Source B
In Figure 5, source A and source B share common negative terminal connections.
Figure 5 Connecting Source A and Source B with Common Negative Terminals
In Figure 6, 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 5, discharging does
not occur and there is no restriction requiring that source A and source B voltages be equal.
A-
127037
A+
B+
B-
+
A-
A+
B+
B-
+
A-
127039
A+
B+
B-
Va
Vb
+
+
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