Use a 6 AWG wire rated 75°C minimum, for DC power modules connection. The system accepts a nominal input voltage of -48 VDC or -60VDC, with an operational tolerance range of -40.5 to -72 VDC. One dedicated, commensurately rated DC power source is required for each power module connection. Each power feed shall be provided with a double pole breaker, rated not more than 60A, with medium delay.

Note	Follow the power and sizing requirements for your site.

Note	The Short Circuit protection Breaker shall not be rated more than 60A.

Power redundancy requirements vary based on the system configuration (number of cards present in the chassis and traffic load). DC-powered systems are N+1 protected.

Power connections to the power tray for each DC power module requires four cables: two source cables and two return cables.

For DC power cables, we recommend 6 AWG high-strand-count copper wire cables, rated 75°C minimum. The size of the cables depends on your chassis location from the source power. Follow your local practices for determining cable size. DC power cables are not available from Cisco, but they are available from any commercial cable vendor.

You must terminate DC power cables using cable lugs at the power tray end. The lugs required for the input power are provided with the power modules.

Warning

Hazardous voltage or energy may be present on power terminals. Always replace cover when terminals are not in service. Be sure uninsulated conductors are not accessible when cover is in place. Statement 1086

Warning

Only trained and qualified personnel should be allowed to install, replace, or service this equipment. Statement 1030

Note	Before connecting DC power cables to the power system, make sure that the input power cords are not energized.

Note	Ensure that there is a readily accessible disconnect device incorporated in the building’s installation wiring.

Note	Circuit breaker and fuse lockout procedures should follow the rules and regulations in the National Electrical Code (NEC) and any local codes.

Warning

To avoid shock hazard, be sure to apply shrink wrap tubing around the wire entry area of the lug.

The color coding of source DC power cable leads depends on the color coding of the site DC power source. Because there is no color code standard for source DC wiring, be sure that power source cables are connected to the power modules using the proper positive (+) and negative (–) polarity:

• In some cases, the source DC cable leads might have a positive (+) or a negative (–) label. This is a relatively safe indication of the polarity, but you must verify the polarity by measuring the voltage between the DC cable leads . Be sure that the positive (+) and negative (–) cable leads match the positive (+) and negative (–) labels on the power module when making the measurement.
• A green (or green and yellow) cable typically indicates that it is a ground cable.

Caution

DC power modules contain reverse voltage protection circuitry to prevent damage to the power module if it detects a reverse polarity condition. No damage should occur from reverse polarity, but you should correct a reverse polarity condition immediately.

The rating label is shown in the figure below.

Observe the following guidelines for DC-powered shelves. In addition, be sure to review the requirements described in theGeneral Power and Grounding Requirements .

• A DC-powered chassis requires up to a maximum of 12,250 watts of DC input power when the chassis is fully loaded.
• All power connection wiring must conform to the rules and regulations in the National Electrical Code (NEC) and any local codes. In addition, make sure that the wiring conforms to any internal requirements at the installation site.
• Each DC power source must comply with the safety extra-low voltage (SELV) requirements in UL 60950-1, CSA-C22.2 No. 60950-1, EN60950-1, AS/NZS 60950, and IEC60950-1.
• A DC-powered system should be installed in a restricted access area in accordance with the National Electric Code, ANSI/NFPA 70.
• All components in the area where DC input power is accessible must be properly insulated.

If it is not possible to rely on the identification of the earthed conductor in the DC mains supply, whereby the equipment is not provided with a two-pole disconnect device, then a two-pole disconnect device is to be provided external to the equipment.

You must connect the central office ground system or interior equipment grounding system permanently to one of the two supplemental bonding and grounding connections on the back or side of the chassis to meet Network Equipment Building System (NEBS) requirements as well as safety compliance requirements. These grounding points are referred to as the NEBS bonding and grounding points.

Note

These bonding and grounding connections satisfy the Telcordia NEBS requirements for supplemental bonding and grounding connections. If you are not installing the chassis in a NEBS environment, you can choose to bypass these guidelines and rely on the safety earth ground connections to the DC power modules.

There are five grounding points on the Cisco NCS 4000 FCC as seen in the figure below.

To ensure a satisfactory supplemental ground connection to the chassis, use the following parts:

• One grounding lug, which has #10 stud holes with 5/8 spacing between them, and a wire receptacle able to accept a 4-AWG or larger, multistrand copper wire. This lug is similar to those used for the DC input power supply leads.
• Two M6 round-head screws and two locking washers.
• One grounding wire. Although we recommend at least 4-AWG multistrand copper wire, the wire diameter and length depend on your chassis location and site environment.

To reconnect DC power to a DC power tray, see Connecting Power to a DC-Powered Chassis.