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Earth Ground Fault Troubleshooting
An 
indicates that the panel has detected a short between any terminal on the
panel and earth ground. To determine the location of the short, place a DC
volt meter with ground on terminal 22 (circuit ground) and positive on any
of the screws that secure the circuit board to the cabinet (earth ground).
A typical meter reading should indicate a voltage of approximately 10.85 VDC. Any reading lower than 8.5 VDC or higher than 13.1 VDC will put the panel into "Earth Fault Trb". Remove and leave off field wiring from the panel until the meter reads in the normal range (about 10.85 VDC).
When an "Earth Fault Trb" is indicated at the touchpad two messages will be added to the event history buffer. "Expand Trb 38" and "Earth ###". This information can be very helpful to identify where an earth ground fault exists in an intermittent earth ground situation.
If the "Earth ###" is lower than 74 this typically would indicate an earth ground short to a low voltage source (8.5 VDC or less). For example, any circuit ground terminal or zone input terminal.
If the "Earth ###" is higher than 114 this typically would indicate an earth ground to a higher voltage source (13.1 VDC or higher). For example, any circuit power, standby battery, phone lines, or AC Power.