Juniper MX2020 Hardware Manual page 232

The fan trays in an optimized DC power subsystem draw power from the power zones differently than
the fan trays in a base DC power subsystem. In a base DC power subsystem, two of the four fan trays
draw power from both zones. In the optimized DC power subsystem, two of the fan trays draw power
from only one zone. Because of this, the optimized power subsystem requires less power. Since the two
fantrays share power in a zone, they only require 100% of the power they are rated at (not 140%). This is
a net savings of 40% * 1700W/fantray * 2 for the system and half that amount per power zone.
NOTE: 70% of the total power from zone 0 + zone 1 must be provided by EACH zone in the
calculation.
NOTE: Four DC Power Supply Modules (PSMs) per zone are mandatory for the MX2020 router
with DC Power Distribution Modules (PDMs).
As illustrated in Figure 76 on page 210
MX2020 DC base power subsystem distribute power to FRUs as follows:
Zone 0 powers only line card slots 0-9, and fan tray 1
Zone 1 powers only line card slots 10-19, and fan tray 3
Zone 0 + Zone 1 (both zones provide power) to CB-RE slot 0 and CB-RE slot 1, fabric card slots 0-7, and
fan tray 0 and 2
Figure 76: Power Distribution in a DC Base Power Subsystem
and described in Table 75 on page 211, the power zones in the
210