Use a meter to test the resistance between the Equipment Grounding Conductor (EGC) and the Grounded Current Carrying Conductor; most call this the neutral.
If you get any measurable value you may have found the problem. A fault between the EGC and the energized conductor will trip a GFCI immediately on every attempt to reset it. A fault in the neutral that allows current to flow to the EGC will only trip the GFCI when a load is applied and current is flowing. Any load on that circuit that operates somewhat randomly could be the culprit. Examples include refrigerators and freezers, sump pumps, garage door openers, lighting timers or motion sensers...
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Tom
If you get any measurable value you may have found the problem. A fault between the EGC and the energized conductor will trip a GFCI immediately on every attempt to reset it. A fault in the neutral that allows current to flow to the EGC will only trip the GFCI when a load is applied and current is flowing. Any load on that circuit that operates somewhat randomly could be the culprit. Examples include refrigerators and freezers, sump pumps, garage door openers, lighting timers or motion sensers...
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Tom