Cisco 3845 Hardware Guide - Page 55
Connecting to One Source Only-Source A or Source B - dc power supply
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UPC - 746320981420
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Page 55 highlights
Power Connections 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 A- A- + + A+ A+ B+ B+ B- B- 127037 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 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. OL-5970-02 Connecting Cables to Cisco 3800 Series Routers 25
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