3Com 4500G Series, Руководство по началу работы

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Connecting a Redundant Power Supply 25
WARNING: When powering any Switch 4500G from an RPS, make sure that the
unit is earthed (grounded) by either connecting the power cord to the unit or by
connecting the earth terminal on the rear of the unit to a reliable electrical earth
(or by connecting both). Ensure that the earth connection is made before
connecting the DC supply from the RPS.
3Com switches that support -48V DC RPS inputs, and are PoE enabled, can only
be powered by an RPS that complies with the isolation requirements of IEEE-Std
802.3af. Non PoE enabled switches do not have this restriction.
WARNING : Do not use a standard 'positive-earthed' -48V redundant power
system suitable for use with telecommunications equipment with the 3Com
Power-over-Ethernet (PoE) network switches. In order to meet the IEEE 802.3af
(PoE) specification, the -48V output must be isolated from earth (ground) and
meet the isolation requirements in that specification.
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 4500G DC supply input are provided
in Table 11 on page 19.
You can power the Switch 4500G using three methods:
■
AC Mains only — this does not offer any power redundancy. If the AC mains
supply or the AC power supply fails, the switch powers 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 environments where only DC power
is available.
The RPS provides two main benefits:
■
Power Redundancy — if a switch is powered from the mains supply unit, a
failure of the internal power supply causes the switch to fail. You can avoid this
by connecting both the AC and DC RPS supplies to the switch. You can also
add redundancy to the DC power by using (N+1) DC power supplies to further
increase the availability of the system.
■
Uninterruptable Power — the system allows easy connection and
maintenance of batteries to the RPS shelf to further increase the availability of
the system.
Specifying the
Redundant Power
System
3Com’s redundant power solution allows you to use any off-the-shelf -48V DC
RPS that meets the requirements defined in Table 11 on page 19.
For an approved vendor list, more details about purchasing the 3Com
recommended RPS, and a full set of requirements go to:
http://www.3Com.com/RPS
The 3Com recommended RPS generates -48V DC power using power supply units
(or rectifiers). The outputs of the rectifier(s) are connected together so that you
can increase the total -48V power available by adding rectifiers. For example, three