Input-Power-Present Leds; Dc Power Wire Characteristics - Cisco Carrier Routing System CRS-1 Installation Manual

Chapter 2 Installing and Removing Power Components

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
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 2-11 Input-Power-Present LEDs
B1
+ B1 + B0
– –
(RTN) (-48V/-60V) (RTN) (-48V/-60V)
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

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 –48 VDC (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
references are for planning purposes and might be further subject to local laws and practices.
Table 2-3
measurement are in American wire gauge (AWG).
OL-10971-10
ON
B0
ON SIDE B
B1 B0
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.
2-3. For the resistance of 1000 feet of copper wire for each gauge of wire, see
provides the gauges of wire needed for wire lengths and DC power currents. The units of
Cisco CRS Carrier Routing System 4-Slot Line Card Chassis Installation Guide
DC Power Systems on the Cisco CRS 4-Slot Router
Figure 2-11). The LED provides a warning
ON
A1 A0
+ A1 + A0
–
(RTN) (-48V/-60V) (RTN) (-48V/-60V)
SIDE A ON
A1 A0
–
Table 2-4. These
2-11