Cisco WS-C2950T-24 Hardware Installation Guide - Page 105
Approved Scenarios and Scenarios Not Approved for Dual DC Power Supply Configuration on Cisco 2911
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Chapter 3 Installing and Connecting the Router Connecting Power Approved Scenarios and Scenarios Not Approved for Dual DC Power Supply Configuration on Cisco 2911, 2921, and 2951 Routers You can connect a single DC power source to either the A input or the B input. If there are dual power sources, connect one source to the A input and one source to the B input. Both sources must be the same polarity (with respect to ground) and voltage (within 0.25 volts). Do not connect -DC grounded and +DC grounded dual sources to Cisco 2911, Cisco 2921, and Cisco 2951 routers. Caution Dual sources with opposite-polarity grounding damage equipment. In Figure 3-23, either the positive source terminal or the negative source terminal is tied to ground. Figure 3-23 Connecting to One Source Only-Source A or Source B In Figure 3-24, source A and source B share common negative terminal connections. Figure 3-24 Connecting Source A and Source B with Common Negative Terminals In Figure 3-25, 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 OL-18712-01 Cisco 2900 and 3900 Series Hardware Installation 3-23