Specifications

Reference Guide
3-19
System Installation System Power and Ground Connections
3.6.3 Power Enhanced Chassis with Power Supplies in Front (891930)
Figure 3-12 shows the terminal block on the front-loading chassis with power enhancement
on top. Although the terminal block is oriented vertically on this chassis, it provides an
improved external terminal block that requires additional jumpers to provide power to user
cards that apply voltage to the CPE device.
The
V
NA
and
V
NB
leads were added to provide an interface for a separate, redundant or
non-redundant power source to the system. The
V
NA
and
V
NB
leads are no longer referenced
to the
V
A
and
V
B
leads respectively. As a result this condition if you are running a DC system
with -48VDC connected to the
V
A
(F1 Power Supply) or
V
B
(F2 Power Supply) leads, you
will not have any battery applied to any of the user cards that require the -48VDC towards the
CPE equipment. There must be a separate source applied to the
V
NA
or
V
NB
leads to provide
the -48VDC source to the connecting CPE equipment. If a second source is not available you
may install a jumper from the
V
A
or
V
B
source leads using 16 gauge wire. The
V
A
or
V
B
source feed must also be 16 gauge wire if a jumper between leads is required.
The telecommunications voice signaling ground is referenced ground connection to the
V
NA+
side or
V
NB+
side of the -48VDC power system. Both of these feeds are referenced to the same
place on the backplane. This reference ground can occur at the integrated access system power
connection strip or at the -48VDC power source, which ever is more effective if having
multiple connections back to a ground source is not desirable. The wire connection between
the
V
NA+
,
V
NB+
,
V
A+
, or the
V
B+
terminals, and a referenced ground is required to eliminate
ground isolation between connection devices.
If this ground connection is not maintained,
and one side of the connection equipment is not referenced to an earth ground then a
floating ground condition can occur causing the voice circuits and the voice signaling to
react erratically when either end of the connecting equipment tries to start the circuit.
When running the system in an AC environment with an AC/DC converter installed in the
chassis, the
V
NA+
or
V
NB+
must have the same ground reference as the connecting equipment
so as not to produce a floating ground potential as discussed earlier.
Sites using only loop start telecommunication circuits (no ground start or E&M signaling) can
operate properly without the Telecom Signaling Ground.
When grounding the system, you may use 14 gauge solid wire for a single connection to the
terminal block connector. When there is no way to provide multiple separate ground feeds you
may use 16 gauge solid wire to connect from one terminal block pin to another terminal block
pin with a ground feed on one of the terminal block pins that are looped together. If you use
different gauge wire on the feed terminal block pin and the looped terminal block pins the
connection may not have the proper integrity due to the larger size wire impeding a solid
connection to the smaller wire.
In all previous versions, the chassis and ground was either tied together via the terminal block
connector or when the logic cards were inserted and secured with the panel screws. This
caused the ground scheme of the system to be automatically tied together via the logic card.