Dc Power Wire Characteristics - Cisco CRS-1 System Description

Chapter 2 Chassis Power System

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 protective earth conductor
must be large enough to carry all the current if the –48 VDC return fails. 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 2-4
We recommend using at least 50-A of DC current and 6-gauge wire.
Note
Table 2-4 Wire Gauge for Current Loads over Copper Wire Lengths
DC Current (Amps) 25 Feet
5-A 18 gauge
10-A 14 gauge
15-A 14 gauge
20-A 12 gauge
25-A 12 gauge
30-A 10 gauge
35-A 10 gauge
40-A 8 gauge
45-A 8 gauge
50-A 8 gauge
55-A 8 gauge
60-A 8 gauge
65-A 6 gauge
70-A 6 gauge
75-A 6 gauge
100-A 4 gauge
Table 2-5
wire) for copper wire.
OL-10805-10
2-4. 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.
50 Feet 75 Feet
14 gauge 14 gauge
12 gauge 10 gauge
10 gauge 8 gauge
8 gauge 8 gauge
8 gauge 6 gauge
8 gauge 6 gauge
6 gauge 4 gauge
6 gauge 2 gauge
6 gauge 4 gauge
4 gauge 4 gauge
4 gauge 2 gauge
4 gauge 2 gauge
4 gauge 2 gauge
4 gauge 2 gauge
4 gauge 2 gauge
2 gauge 1 gauge
provides the correlation between wire gauge and the resistance (in Ohms for each 1000 feet of
Cisco CRS Carrier Routing System 4-Slot Line Card Chassis System Description
100 Feet 150 Feet
12 gauge 10 gauge
8 gauge 8 gauge
8 gauge 6 gauge
6 gauge 4 gauge
4 gauge 4 gauge
4 gauge 2 gauge
2 gauge 2 gauge
2 gauge 2 gauge
2 gauge 1 gauge
2 gauge 1 gauge
2 gauge 0 gauge
2 gauge 0 gauge
1 gauge 0 gauge
1 gauge 00 gauge
1 gauge 00 gauge
00 gauge 000 gauge
DC Power System
Table 2-5. These
200 Feet 400 Feet
8 gauge 6 gauge
6 gauge 2 gauge
4 gauge 2 gauge
2 gauge 0 gauge
2 gauge 0 gauge
2 gauge 00 gauge
1 gauge 000 gauge
0 gauge 000 gauge
0 gauge 0000 gauge
00 gauge N/A
00 gauge N/A
00 gauge N/A
000 gauge N/A
000 gauge N/A
000 gauge N/A
N/A N/A
2-11