Cisco Systems 3700 Series manual 3-16, A A+ B+ B

Chapter 3 Installing the Router

Power Connections

In Figure 3-19, source A and source B share common negative terminal connections.

Figure 3-19 Connecting Source A and Source B with Common Negative Terminals

Va

+

+

Vb

A-

A+

B+

B-

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In Figure 3-20, 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 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 3-19, discharging does not occur and there is no restriction requiring that source A and source B voltages be equal.

Cisco 3700 Series Routers Hardware Installation Guide

3-16 OL-2180-08