Cisco Gigabit Switch Router 12008 Installation And Configuration Manual page 302

Adding, Removing, or Replacing a DC-Input Power Supply
To add a second (redundant) DC-input power supply to the router, perform the following
steps:
Step 1
Warning
that will be used to service the new power supply, use a voltmeter to measure the voltage
across the negative (–) and positive (+) source DC leads to be connected to the power
supply. Set the voltmeter to a range that makes it capable of measuring up to 75 VDC. The
measurement across the positive and negative leads should be zero (0) volts.
Step 2
Step 3
Step 4
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Cisco 12008 Gigabit Switch Router Installation and Configuration Guide
Locate the source DC circuit breaker that will service the DC-input power
supply; ensure that this circuit breaker is set to the OFF position. For added
safety, tape the circuit breaker handle in the OFF position.
The color coding scheme used for the source DC power cables for the
Note
DC-input power supply depends on the scheme used for the site DC power
source. Typically, green or green/yellow is used for earth ground, red is used for
positive (+), and black is used for negative (–). Make certain that you properly
map the color coding scheme used at the site for the DC power source to the
proper terminals on the DC-input power supply faceplate.
To be completely sure that power has been removed from the source DC circuit
Using a 1/4-inch flat-blade screwdriver, loosen the captive installation screw on
the blank filler panel covering the vacant (upper) power supply bay; remove the
filler panel and retain it for possible future use.
Presumably, you will be installing the new power supply in the upper power
supply bay, since, by convention, a single DC-input power supply is installed in
the lower bay.
Ensure that the rotary power switch on the faceplate of the new power supply
that you will be installing is set to the OFF (O) position.
Grasp the carrying handle on the new power supply with your left hand; while
lifting the power supply, place your right hand beneath the unit to support its
weight.