Cisco 3800 Series - Manual (Page 55)

Power Connections
25
Connecting Cables to Cisco 3800 Series Routers
OL-5970-02
Caution Dual sources with opposite-polarity grounding damage equipment.
In Figure 16 , either the positive source terminal or the negative source terminal is tied to ground .
Figure 16 Connecting to One Source Only—Source A or Source 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
In Figure 18 , source A and source B share common positive terminal connections. This configuration is
allowed only if Va equals Vb (within 0.25 V).
Caution If source A and source B are wired with common positive terminals and their voltages are unequal by
more than 0.25 V, the higher-voltage source can discharge into the lower-voltage source through the
negative terminals. Excessive discharging currents through these terminals can actuate one or both of
the dual- input DC power supply’s internal A– or B– fuses, resulting in lack of redundancy or system
failure. When source A and source B are within 0.25 V, discharge current is minimal.
A-
127037
A+
B+
B-
+
A-
A+
B+
B-
+
A-
127039
A+
B+
B-
Va
Vb
+
+