Specifications

Revision: 2008-02-07 5-1
5 Powering
5.1 Plug-in
Each plug-in is fed via subrack backplane with (dual) -48VDC (referenced to
0VDC of the exchange battery). The minirack mechanics has two -48VDC inputs
and on model SZ.876.V100 also an AC powering input. The plug-in generates
the used voltages onboard.
The ground reference of all voltages on the secondary side of the plug-in DC/DC-
converter is tied to FPE (Functional Protective Earth).
Additionally, the plug-in is fed over the backplane with an auxiliary +5VDC supply
(referenced to ground) generated on the ACU. The only purpose of this voltage is
to drive the alarm circuitry on each plug-in, even in the case of a failure of the
plug-in onboard DC/DC-converter.
5.2 Tabletop
5.2.1 Power and Grounding
The ground of a tabletop modem is normally floating when referenced to earth. If
a tabletop modem is equipped with an E1 or nx64 kbit/s user interface, the
shields / signal ground of the cables are coupled to the ground of the modem. On
tabletop modems a ground connector is available on the rear panel of the mo-
dem.
A slide switch located on the rear of the housing selects the power source of the
tabletop unit (remote powering over the DSL line or local powering by an external
48VDC source).
The position of the switch can be changed with a small screwdriver. Before oper-
ating the switch, the DSL line connector and the mains adapter connector must
be removed.
Caution:
Switching from local to remote powering leads to an interruption of the DSL link.
Before changing the position of the powering switch the tabletop must be
switched off and disconnected from the DSL line.