Pittway NOTIFIER AM2020 Troubleshooting Manual page 8

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The capacitive reactance formula can also be used to find the maximum
allowable capacitance before an induced ground fault will result.
solving the formula for C (Capacitance) yields;
substituting the ground fault circuits frequency and threshold;
Figure 2-6: Calculating the maximum allowable capacitance
before a ground fault will be induced
The result is approximately 12.73 microfarads. The capacitive reactance (X
inversely related to the capacitance value. So, as the capacitance goes up, the
capacitive reactance goes down. If it goes below 50,000 ohms a ground fault will
result. That means that 12.73 microfarads is the maximum allowable amount of
capacitance collectively on all loops leaving the panel.
Figure 2-7: Schematic representation of a typical
ground fault condition caused by capacitance
Note: A ground fault is not caused by the failure to connect earth ground to the system.
Corrective Action:
The most efficient way of troubleshooting a ground fault is to isolate the panel
from the field wiring by removing circuits one at a time and leaving them off
until the problem source has been identified.
1) Disconnect all SLC loops from the panel by removing the detachable
terminal blocks from each LIB and wait for approximately one minute to
see if the ground fault clears.
AM2020/AFP1010 Troubleshooting Guide 50432 Revision A 8/13/97
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