3Com 4200G Series, Getting Started Manual

Page: 29 / 90

Connecting a Redundant Power Supply 29
WARNING: When powering any Switch 4200G 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. This restriction does not apply to non
PoE enabled switches.
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 4200G DC supply input are
provided in Appendix C on page 127 .
You can power the Switch 4200G 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 the following main benefits:
■
Power Redundancy — if a switch is powered from the main 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 system availability.
■
Uninterruptable Power — you can easily connect and replace the
RPS shelf batteries, which further increases system availability.
10014914_AB_Switch 4200G.book Page 29 Tuesday, October 2, 2007 12:13 PM