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Cisco MGX 8220 Installation and Configuration
Release 5.0, Part Number 78-6430-03 Rev. D0, November 2003
Chapter
Cooling Assembly
DC Power Drain and Circuit Protection
Each card in an Cisco MGX 8220 shelf draws an average of 21W with a worst-case shelf current of
14.40A.
The circuit breaker in the DC power entry module (PEM) is rated at 15.00A.
The Cisco MGX 8220 circuits are protected as follows:
• Backplane has a 5A fast-blow fuse for each slot position.
• Each board has a 1.5A circuit breaker in the -48V DC line to the DC/DC converter.
Each Cisco MGX 8220 board is equipped with a DC/DC converter (Shindengen—HGG05006 or
AT& T—JW030A), which has an automatic current limited to 5V output.
A schematic of the DC power system is shown in Figure 2-6.
Figure 2-6 DC Power System
Cooling Assembly
This section describes the cooling assembly that cools the Cisco MGX 8220 shelf and equipment:
• Main Cooling Assembly, page 2-7
• Booster Cooling Assembly, page 2-8
• Plenum Exhaust Chamber, page 2-8
• Spacer Unit, page 2-8
• Cooling Assembly Power, page 2-8
The main cooling unit houses the fans that circulate air through the shelf. This unit is mounted below
the shelves. This unit is capable of cooling up to two Cisco MGX 8220 shelves in the same rack. Racks
that contain more than two shelves require a booster unit to provide additional cooling. The cooling
assembly is powered from the main shelf.
The plenum or a spacer unit is mounted above the shelves to exhaust the warm air.
A single Cisco MGX 8220 shelf is shown in Figure 2-7. For more information on rack assembly and
configuration, see Chapter 7, “Installation and Start-Up.”
PEM
B
A
C
K
P
L
A
N
E
Battery
power
-48V
RTN
Safety
ground
-48V
-48V
RTN
RTN
DC/DC
converter
Conductive edge
Circuit board
Earth ground
Safety ground
H8248