3Com 4500 Getting Started Manual page 23

Switch 4500 family 26/50-port
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Connecting a Redundant Power Supply to your Switch 4500 PWR
WARNING: Any RPS must be approved as a SELV output in accordance with IEC
60950-1/UL 60950-1/EN 60950-1.
WARNING: The characteristics of the Switch 4500 DC supply input are given in
Appendix E "Technical Specifications" on page 79.
The Switch 4500 PWR units can be powered in three different ways:
AC Mains only — does not offer any power redundancy. If the AC mains
supply or the AC power supply fail, the Switch will power off.
AC Mains and -48V DC (primary supply) — the internal AC supply acts as
the backup in the event of a DC power failure.
DC only — the Switch does not need an AC supply and the resiliency is
provided by the DC supply. This is useful in an environment where only DC
power is available.
The RPS provides three main benefits to the customer:
Power Redundancy — if a Switch is powered from the mains supply unit, a
failure of the internal power supply will cause the Switch to fail. This can be
overcome by connecting both the AC and DC RPS supplies to the Switch.
Additional redundancy can also be added to the DC power by using (N+1) DC
power supplies to further increase the availability of the system.
Uninterruptible Power — the system allows easy connection and
maintenance of batteries to the RPS shelf to further increase the availability of
the system.
Additional Power to PoE Ports — the internal AC Power Supply of a PoE
Switch can provide enough power for most network applications. The RPS can
be used to supplement additional power (up to a maximum of 15.4W),
including full backup of all PoE devices on the network.
Table 7 below, outlines the behavior of the Switch when changes occur to the
power system, such as removing the AC mains cable when the RPS is attached.
The responses to the different power inputs are controlled by the Switch's internal
power supply and not by the RPS.
23

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