Mitel SX-200 EL, Technician'S Handbook

Page: 73 / 262

Troubleshooting and Repair
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Ground Path AC Voltage Test
This test measures the presence of AC voltage in the metallic loop.
1. With your meter connected in the same way as you did for the resis-
tance test, measure the AC voltage.
2. Start with your meter set for high AC voltages and adjust it down
until you get a reading.
3. You should get a reading of 1 Vac or less.
If your reading is greater than 1 Vac, check to see if your electrical panel
ground connects to the building ground. Depending on local utility
regulations, the connection usually exists between the electrical panel
ground and a cold water pipe entering the building. If this connection is
present, try an alternate ground point(s) and measure the AC voltage
again.
If the system ground and safety ground both connect to the building
ground, your measurement is the metallic loop from the PBX chassis,
to the electrical panel ground, to the cold water pipe, and back through
the system ground wire.
If the safety ground and system ground do not connect at the electrical
panel, your measurement indicates the AC voltage differential between
protective earth and the building ground.
Ground Path Resistance Test
1. Turn off the main PBX system circuit breaker.
2. At the PBX system, connect the cabinet’s chassis ground to the
electrical panel ground. The wire should be a minimum 10 AWG and
not longer than 15 meters.
3. At the PBX system, disconnect the ground wire from the system’s
ground-stud.
4. Set your meter to OHMS at the highest scale.
5. Measure the resistance between the PBX chassis safety ground
and the ground wire that provides the system ground. Adjust your
meter down until you get a reading.