Cisco 3845 Quick Start Guide - Page 21

Figure 16 Connecting to One Source Only-Source A or Source B A- A- + + A+ A+ B+ B+ 127037 B- 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 AVa + A+ + B+ Vb B- 127039 In Figure 18, 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 Aand 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 17, discharging does not occur and there is no restriction requiring that source A and source B voltages be equal. 21