Memotec NetPerformer SDM-9220 Series, Hardware Installation Manual, Page: 69 / 146

Hardware Installation
Memotec Inc. 4-23
4.9.1 E&M Grounding Considerations
Proper grounding is essential for correct operation of telephone equipment in E&M
applications. E&M signaling works by applying DC voltages to the E and M leads for
connecting and disconnecting. Without a proper ground, the DC voltages do not have a
common point of reference, which can result in unintended or sporadic signaling.
Distance may be an important factor for an E&M interface on the SDM-9220 UAC and
SDM-9230 UAC. If the PBX and the NetPerformer UAC unit are not near each other (in
the same room, for example) then their AC grounds may not be the same. To avoid
grounding problems on the UAC unit, ensure that your installation respects the following
conditions:
• Check the distance between the PBX and the NetPerformer UAC unit.
- If the two are not within close proximity, then their AC grounds may not be
the same.
- If the NetPerformer UAC unit and the PBX are in the same room, it is likely
that they share the same AC ground.
• In an E&M application, the common ground must be the Telco/PTT ground. This
ensures that the ground potential of the PBX telephone interface and the NetPer-
former telephone interface are the same.
Based on the above conditions, grounding may be established directly or indirectly.
•
Direct Method
:
Connect a grounding wire between the Telco/PTT interfaces on
the PBX and the NetPerformer UAC unit.
- Connect the ground wire from the PBX to pin 8 (SG) of the RJ45 connector
on the E&M interface card.
This will establish the same ground potential at both interfaces.
•
Indirect Method
:
If direct grounding is not possible or practical, establish an indi-
rect ground.
- Make sure the Telco/PTT grounds of the PBX and the NetPerformer UAC unit
are connected to their respective AC grounds.
Check with the PBX manufacturer for information on how to connect the
PBX AC ground to the Telco/PTT ground.
- The AC grounds of the two devices must be at the same potential, which is
usually the case when they are located in close proximity.
Caution:
Connecting the AC ground to the Telco/PTT ground on tele-
phone equipment may violate the rules of certain regulatory agencies. For
complete grounding regulations, please check with your local telephone
company and/or agency.