Cisco 3725 Hardware Installation Guide - Page 62

Connecting Source A and Source B with Common Negative Terminals

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Power Connections Chapter 3 Installing the Router In Figure 3-19, source A and source B share common negative terminal connections. Figure 3-19 Connecting Source A and Source B with Common Negative Terminals AVa + A+ + B+ Vb B- 127039 In Figure 3-20, 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 3-19, discharging does not occur and there is no restriction requiring that source A and source B voltages be equal. 3-16 Cisco 3700 Series Routers Hardware Installation Guide OL-2180-08

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3-16
Cisco 3700 Series Routers Hardware Installation Guide
OL-2180-08
Chapter 3
Installing the Router
Power Connections
In
Figure 3-19
, source A and source B share common negative terminal connections.
Figure 3-19
Connecting Source A and Source B with Common Negative Terminals
In
Figure 3-20
, 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 3-19
, discharging
does not occur and there is no restriction requiring that source A and source B voltages be equal.
A-
127039
A+
B+
B-
Va
Vb
+
+