2-8
Catalyst 4500 E-Series Switches Installation Guide
OL-13972-02
Chapter 2 Preparing for Installation
Site Requirements
Besides these appliances, the greatest threats to a system power supply are surges or blackouts that are
caused by electrical storms. Whenever possible, turn off the system and any peripherals, and unplug
them from their power sources during thunderstorms. If a blackout occurs—even a temporary
one—while the system is turned on, turn off the system immediately and disconnect it from the electrical
outlet. Leaving the system on may cause problems when the power is restored; all other appliances left
on in the area can create large voltage spikes that can damage the system.
System Grounding
You must install a NEBS-compliant system ground as part of the chassis installation process. Chassis
installations that rely only on the AC third-prong ground are insufficient to properly and adequately
ground the systems.
The system (NEBS) ground is different than the source power ground (AC third-prong ground on an AC
power plug). The source power ground is designed for safety in the case of a short circuit in the power
supply or a connection between the live voltage wire and the chassis. The resulting short circuit causes
the source power circuit breaker to trip, which minimizes the damage to the chassis and the possible
shock hazard to anyone in physical contact with the chassis. The source power ground usually does not
have low impedance, it might be shared across many different types of devices, and it can have a floating
voltage with reference to true earth ground.
The system (NEBS) ground should have the lowest possible impedance to true earth ground to ensure
that there is no floating voltage. The system (NEBS) ground should have only communications
equipment connected to it and should be free of induction or capacitance-induced voltages. In order to
reduce the possibility of spurious signals and floating voltages from disrupting data transmissions, it
might be necessary to install a new dedicated system (NEBS) ground in your data center.
You must observe the following system grounding guidelines for your chassis:
•
You must install the system (NEBS) ground connection with any other rack or system power ground
connections that you make. The system (NEBS) ground connection is required if FXS modules are
installed or if this equipment is installed in a U.S. or European central office.
•
You must connect both the system (NEBS) ground connection and the power supply ground
connection to earth grounds.
Caution
Installations that rely solely on system grounding using only an AC third-prong ground run a
substantially greater risk of equipment problems and data corruption than those installations that use
both the AC third-prong ground and a properly installed system (NEBS compliant) ground.
Table 2-1
lists some general grounding practice guidelines.
