Cisco Systems Cisco 12816 Manuale Utente

DC PEMs contains circuitry to trip the breaker on the PEM if the PEM detects a 
reverse polarity condition. No damage should occur from reverse polarity, but you 
should correct a reverse polarity condition immediately.

For a list of the nominal and acceptable value ranges for source DC power, refer 
to 

Although the router chassis requires a safety earth ground connection as part of 
the power cabling to the power shelf, we also recommend that you connect the 
central office ground system or interior equipment grounding system to the 
supplemental bonding and grounding connections.

Supplemental connections are located at the top of the power interface panel on 
the back of the chassis (

), and near the lower corners of the switch 

fabric card cage on the front flanges of the chassis (

). The DC return 

of this system should remain isolated from the system frame and chassis (DC-I).

This grounding points are also referred to as the network equipment building 
system (NEBS) bonding and grounding connections. 

These bonding and grounding connections satisfy the Telcordia NEBS 
requirements for supplemental bonding and grounding connections. If you are not 
installing the router in a NEBS environment, you can choose to bypass these 
guidelines and rely on the safety earth ground connections to the AC and DC 
power shelves.