M120 DC Power, Connection, and Cable Specifications
In the DC power configuration, the router contains two DC power supplies (see DC Power Supply), located in the right rear of the chassis in slots PEM0 and PEM1 (left to right). A single DC power supply provides sufficient power for a fully configured router.
Two DC power supplies share power almost equally within a fully populated system. If either power supply fails, the remaining power supply takes over without interruption.
Each DC power supply has a single DC input (–48 VDC and return) that requires a dedicated 60 A (–48 VDC) circuit breaker for the maximum router hardware configuration.
Most sites distribute DC power through a main conduit that leads to frame-mounted DC power distribution panels, one of which might be located at the top of the rack that houses the router. A pair of cables (one input and one return) connects each set of terminal studs to the power distribution panel.
 | Note: If you plan to operate a maximally configured DC-powered router, we recommend that you provision at least 60 A @ –48 VDC for the system. Use a facility circuit breaker rated for 60 A (–48 VDC) minimum for each DC power supply. Doing so enables you to operate the router in any configuration without upgrading the power infrastructure. If you plan to operate a DC-powered router at less than the maximum configuration and do not provision a 60 A (–48 VDC) circuit breaker, we recommend that you provision a circuit breaker for each DC power supply rated for at least 125% of the continuous current that the system draws at –48 VDC. |
 | Caution: You must ensure that power connections maintain the proper polarity. The power source cables might be labeled (+) and (–) to indicate their polarity. There is no standard color coding for DC power cables. The color coding used by the external DC power source at your site determines the color coding for the leads on the power cables that attach to the terminal studs on the power supply faceplate. |
Figure 1 shows a typical DC source cabling arrangement.
Figure 1: Typical DC Source Cabling to the M120 Router
 | Warning: Power plant ground and chassis ground must be connected to the same building ground. |
Table 1 summarizes the specifications for the grounding and power cables, which you supply. The accessory box shipped with the router includes the cable lugs that attach to the terminal studs of each power supply (see DC Power and Grounding Cable Lug). (The cable lug shown in DC Power and Grounding Cable Lug is also used for the grounding the chassis.)
The DC return terminal must be connected to the central office (CO) ground. This common DC return connection (DC-C), and the –48 VDC connection must both be 8 AWG single-strand wire cable (minimum).
| Caution: Before router installation begins, a licensed electrician must attach a cable lug to the grounding and power cables that you supply. A cable with an incorrectly attached lug can damage the router. |
Table 1: M120 DC Power and Grounding Cable Specifications
Cable Type | Quantity and Specification | Maximum Equal Length |
|---|---|---|
Power | Four 6-AWG (13.3 mm2), minimum 75°C wire, or as permitted by the local code | None |
Grounding | One 10-AWG (5.27 mm2), minimum 75°C wire, or as permitted by the local code | None |
Grounding—If the 48 VDC facility is equipped with a circuit breaker rated 80 A (–48 VDC) up to 100 A (–48 VDC), then the grounding cable must be minimum 6 AWG, or as permitted by the local code | One 6-AWG (13.3 mm2), minimum 75°C wire, or as permitted by the local code | None |
| Warning: For field-wiring connections, use copper conductors only. For other electrical safety information, see General Electrical Safety Warnings for M Series, MX Series, and T Series Routers. |
| Caution: Power cords and cables must not block access to router components or drape where people could trip on them. |
The accessory box shipped with the router includes the cable lugs that attach to the terminal studs of each power supply (see DC Power and Grounding Cable Lug). (The cable lug shown in DC Power and Grounding Cable Lug is also used for the grounding the chassis.)
| Caution: Before router installation begins, a licensed electrician must attach a cable lug to the grounding and power cables that you supply. A cable with an incorrectly attached lug can damage the router. |
| Caution: Power cords and cables must not block access to router components or drape where people could trip on them. |
For information about the DC power supply, see M120 DC Power Supply Description. For instructions on connecting the DC power and grounding cables during initial installation, see Connecting Power to a DC-Powered M120 Router. For instructions on replacing a DC power cable, see Replacing an M120 DC Power Supply Cable.
