Chapter 2 Installing and Removing Power Components
DC Power Systems on the Cisco CRS-1 4-Slot Router
Input-Power-Present LEDs
The DC power Input-Power-Present LEDs provide a visual indication to service personnel that there is voltage present across the input terminal’s connections (see Figure 2-6). The LED provides a warning to the service person that there is power present.
Note Power should be disconnected before servicing the input power connections. Always check for hazardous voltage with a multimeter device before servicing the router.
Figure 2-6 Input-Power-Present LEDs
| | | B1 B0 |
+ B1 – | + B0 – | |
(RTN) | (-48V/-60V) | (RTN) | (-48V/-60V) | |
| | | ON | SIDE B |
| | | B1 B0 | B |
| | | |
| | | | Side |
A1 A0
+ A1 – | + | A0 – |
(RTN) (-48V/-60V) | (RTN) | (-48V/-60V) |
SIDE A ON 
A1 A0
A
Side
The input-power-present LED starts to light up when the input voltage reaches 20 VDC; the LED gets brighter as voltage increases. The input-power-present LED is fully lit when the input voltage reaches 38 VDC.
Note If an input-power-present LED is not lit, check for: 1) the presence of voltage, and 2) the polarity of the corresponding wiring block.
DC Power Wire Characteristics
For signal degradation to be averted, a conductor must be large enough to prevent its impedance from creating a voltage drop equal to 2 percent of the reference voltage. Also, the gauge of the earth conductor must be equal to or larger then that of the -48VDC (or -48 VDC return) conductor. This latter requirement is for safety. Full fault redundancy is achieved by having conductors of equal size for the protective earth ground and the -48 VDC return of the switch.
For site preparation, proper wire size and insulation must be selected. For a planned power distribution, calculation must be done prior to distribution to meet the proper voltage drop and temperature rise.
For wire gauges that prevent unacceptable voltage drops over different lengths of copper wire, see Table 2-2. For the resistance of 1000 feet of copper wire for each gauge of wire, see Table 2-3. These references are for planning purposes and might be further subject to local laws and practices.
Table 2-2provides the gauges of wire needed for wire lengths and DC power currents. The units of measurement are in American wire gauge (AWG).
Note Table 2-2and Table 2-3are for reference; we recommend using at least 50-A of DC current and 6-gauge wire.
Cisco CRS-1 Carrier Routing System 4-Slot Line Card Chassis Installation Guide
