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Cisco MGX 8850 Multiservice Switch Installation and Configuration
Release 1.1.31, Part Number 78-11223-03 Rev. B0, May 2005
Chapter 4 Enclosure and Card Installation
Install Electrical Connections
Figure 4-14 Placement of DC Wiring Lugs on the DC-PEM
Swapping a Primary or Redundant DC PEM with Power On
If necessary, you can swap out and replace either a primary or a redundant PEM with power on. To avoid
possibly tripping the system circuit breaker, use the procedure described in this section for disconnecting
and reconnecting the system power cabling.
Caution The cable connector must be disconnected at the backplane end during hot PEM insertion or removal.
If you disconnect the cable first at the PEM, the system power cable is still hot. These hot contacts may
inadvertently touch a surface of the chassis or metal connected to the chassis. If this contact occurs, the
–48 VDC is shorted to the chassis, and the circuit breaker on the still-active PEM opens.
Perform the following steps to remove a PEM with system power on.
Step 1 Turn off the circuit breaker to only the PEM you intend to replace.
Step 2 Turn off the branch circuit at the DC source (the distribution box, for example).
Step 3 Disconnect the three DC source wires at the wiring block on the PEM.
Step 4 Locate the backplane end of the cable for the PEM you intend to replace.
Step 5 At the backplane end of the cable, loosen the captive screws on the cable bracket.
Step 6 Pull the cable bracket out approximately one inch to disconnect the cable.
Step 7 At the end of the cable connected to the PEM, loosen the jack screws and disconnect the power cable
from the PEM.
Step 8 Remove the PEM.
Install a PEM in a System with Power On
Perform the following steps to install a PEM with system power on.
Step 1 Make sure the circuit breaker is in the off position.
Step 2 Insert the PEM and tighten the captive mounting screws.
Step 3 Connect the system power cable first at the PEM.
Connecting the backplane end of the system power cable to the backplane requires some dexterity,
especially if the cabling around the system power cable is dense.
Positive
ground
Safety
ground
-48VDC
H10028