M120 Dc Power, Connection, And Cable Specifications - Juniper M120 Hardware Manual

M120 Multiservice Edge Router Hardware Guide

M120 DC Power, Connection, and Cable Specifications

234
In the DC power configuration, the router contains two DC power supplies (see Figure 15
on page 31), located in the right rear of the chassis in slots
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
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 97 on page 235 shows a typical DC source cabling arrangement.
and (left to right).
PEM0 PEM1
and to indicate
(+) (–)
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