DC
power system description 25
External power distributioh and grounckonnections
The power plants shown in the following ‘figures are typical but there are
many variations possible for the item labeled “Rect/Dist” It could be existing
customer equipment or a system that Northern Telecom either supplies or
recommends. In any case, the rectifier and
@tribution
equipment are
required; the batteries are optional.
Note:
The NT6D52 Switched Mode Rectifier is a QRF12 mounted
within an EM1 enclosure.
In all cases it will be necessary to carefully plan ahead. Refer to the chapter
entitled “Engineering and configuration guidelines.”
Figures 10 through 13 also show the important grounding connections and the
use of the IGB (Insulated Ground Bus). For a general discussion of the
grounding philosophy, see “System grounding.”

General notes for DC figures

Permanent Connection of the rectifier(s) to Branch Circuit
When conduit
or a raceway is used it should be metal and regardless of the
typejt
must
contain an insulated ground wire (green), 6 AWG or larger.
Cord Connection of the rectifier(s) to Branch Circuit
A separate safety-
ground is
always
required when removable line cords are used for the
following reasons:
-
a telephone wire could contact AC elsewhere in the building while the cord
is unplugged (during installation)
-
to minimize hazards from lightning transients when unplugged
-
to minimize the effects of stray grounds (pedestal to floor RS-232 links
to
monitors) during normal operation
This additional safety ground must be 6 AWG or larger, preferably insulated
and must be connected from the pedestal Frame Ground to the Logic Return
Equalizer (with Northern Telecom power units). With customer provided
power, the safety ground must go directly to the ACEG. See Figure 12.
It is preferred that the outlets for rectifier powering be isolated according to
NEC 250-74
and 384-27 (Exception 1).
Power engineering 553-3001-l 52
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