Juniper EX8208 Hardware Manual page 61

How many power supplies you require for N+N redundancy depends on which Junos OS release your
switch is running:
Junos OS Release 10.1 or earlier—Use
or Table 20 on page 60
of N by two.
NOTE: In Junos OS Release 10.1 or earlier, the power management feature manages switches
for N +1 redundancy only. This means, for example, that power management raises an alarm
if there is insufficient power to maintain N +1 redundancy, but not if there is insufficient power
to maintain N+N redundancy.
Junos OS Release 10.2 or later—Use
or Table 24 on page 63
Starting with Junos OS Release 10.2, you can configure the power management software to manage the
switch power for N+N redundancy. When you configure power management for N+N redundancy, power
management lowers the maximum chassis power consumption by lowering the maximum fan speed. It
does so to compensate for the extra power that is held in reserve in an N+N configuration than in an N+1
configuration, because of which less power would ordinarily be available to power line cards. By reducing
the maximum chassis power consumption, power management allows the switch to power more line cards.
The configuration type of the switch and the input voltage determine the number of power supplies needed
(N) for the switch. You must then install additional power supplies to meet the N+N redundancy
configuration. For details about different switch configurations, see
page 27 or EX8216 Switch Configurations.
The tables in this section list the N+N power requirements for different EX8200 switch configurations:
Table 21 on page 62—Lists the N+N power requirements of EX8208 switch configurations that use
2000 W AC power supplies.
Table 22 on page 62—Lists the N+N power requirements of EX8208 switch configurations that use
3000 W AC power supplies.
Table 23 on page 62—Lists the N+N power requirements of EX8216 switch configurations that use
2000 W AC power supplies.
Table 24 on page 63—Lists the N+N power requirements of EX8216 switch configurations that use
3000 W AC power supplies.
Table 17 on page
to determine the number of power supplies needed (N). Then multiply the value
Table 21 on page
in this section.
59, Table 18 on page 60,
62, Table 22 on page 62,
"EX8208 Switch Configurations" on
Table 19 on page 60,
Table 23 on page 62,
61