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Cisco 2900 and 3900 Series Hardware Installation
OL-18712-01
Chapter 3 Installing and Connecting the Router
Connecting Power
Figure 3-31 Connecting to One Source Only—Source A or Source B
In Figure 3-32, source A and source B share common negative terminal connections.
Figure 3-32 Connecting Source A and Source B with Common Negative Terminals
In Figure 3-33, 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.
Note
When source A and source B are wired with common negative terminals, as in Figure 3-32, discharging
does not occur and there is no requirement that source A and source B voltages be equal.
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