Cisco 2811 - Voice Security Bundle Router Hardware Manual page 81

In Figure
Figure 4
+
In Figure
Figure 5
+
+
In Figure
Va equals Vb (within 0.25 V).
When connecting source A and source B with common positive terminals, if source A and source B
Caution
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
does not occur and there is no restriction requiring that source A and source B voltages be equal.
OL-5787-02
4, either the positive source terminal or the negative source terminal is tied to ground
Connecting to One Source Only—Source A or Source B
A-
A+
B+
B-
5, source A and source B share common negative terminal connections.
Connecting Source A and Source B with Common Negative Terminals
A-
Va
A+
B+
Vb
B-
6, source A and source B share common positive terminal connections. This is allowed only if
A-
+
A+
B+
B-
Cable Connection Procedures for Cisco 2800 Series Routers
Power Connections
.
Figure 5, discharging
7