Cisco WS-C2950-24 Hardware Installation Guide - Page 111
Connecting to One Source Only-Source A or Source B
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Chapter 3 Installing and Connecting the Router Figure 3-31 Connecting to One Source Only-Source A or Source B Connecting Power 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. OL-18712-01 Cisco 2900 and 3900 Series Hardware Installation 3-29