Filter
Top Products
32 System grounding
-
Single Point Ground
This system does not, by design, require an isolated AC ground (IG) system
(although local codes may require it). The system does require a single point
ground (SPG) system. The SPG is needed because several conductors are
used as returns. These include battery returns (BR) and logic returns (LR).
Logic return is the name used to bring this particular return out of the pedestal.
But,
internally, several other internal ground returns (also called analog
ground or talk battery return) are connected to the LR.
In its simplest form, the SPG may be the Isolated Ground (IG) bus or AC
Equipment Ground (ACEG) bus in the AC panel. This can be implemented if:
-
The electrical code allows isolated grounds (as per NEC 384-27 exception
1. in the USA).
-
This ground bar located in the AC panel has sufficient terminal points.
-
There is no non isolated communication links to existing PBX or other
communication equipment.
Using an Isolated Ground bus is often a lower cost method but is not allowed
by all telcos and may be prohibited by local ordinances.
An alternate ground
will be needed where an AC panel with an IG bus cannot be provided. When
an alternate SPG is used or where there are too many return conductors to
--
terminate on an IG bus in the AC panel, one or more ground collector nodes
may be required. A grouping of like returns, prior to attaching to the SPG
window is preferred to many long runs of smaller diameter cable. See “List
of terms” for an explanation of these ground nodes.
LRE
A Logic Return Equalizing bus (copper plate or bar) is needed on multi-
column systems where the IG bus in the AC panel is:
-
not being used because of local electrical code requirements
-
too far removed from the pedestals being served
-
too small (insufficient connection points)
-
not expected to be the best ground available (for example, it is known to be
noisy or there is a more direct ground connection)
.d.T.
,>...
.,....
1
‘,
.
,:,
When the LRE function is served by something like an ACIG bus or the LRB
.y:.
2:
_.
+-
-3
..
‘:
+.
bus is also used to terminate system returns other than logic returns, there can
be confusion over terms. In general, large spread out systems require a star-
Power engineering 553-3001-l 52