Cisco 2911, 2921, And 2951 Routers - Cisco WS-C2950-24 Installation Manual

Chapter 3 Installing and Connecting the Router
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.
Dual sources with opposite-polarity grounding damage equipment.
Caution
In Figure
Figure 3-23
In Figure
Figure 3-24
In Figure
if Va equals Vb (within 0.25 V).
When connecting source A and source B with common positive terminals, if source A and source B
Caution
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
3-23, either the positive source terminal or the negative source terminal is tied to ground.
Connecting to One Source Only—Source A or Source B
3-24, source A and source B share common negative terminal connections.
Connecting Source A and Source B with Common Negative Terminals
3-25, source A and source B share common positive terminal connections. This is allowed only
Cisco 2900 and 3900 Series Hardware Installation
Connecting Power
3-23