Fixed The GFCI, Now A Downstream Fault Is Revealed Two-Fault Decision Tree

Why this matters

You replaced a dead or failed GFCI, and now it trips the moment a downstream outlet is loaded, or it will not reset at all. The old GFCI was masking a second fault: while it was dead (or had been bypassed/reset improperly), the load-side circuit never had working ground-fault protection, so a real leakage fault downstream went unnoticed. A working GFCI immediately catches it. This is a two-fault sequence where the first repair restores the protection that exposes the second fault. The mistake is blaming the new device and swapping it again, or worse, moving the downstream wiring to the line terminals to "stop the nuisance trips," which defeats the protection. The new GFCI is doing its job; find the leakage it is catching.

Symptom presentation

After installing a known-good GFCI, it trips on reset or trips as soon as a load plugs into a downstream receptacle, especially in a wet location (bath, kitchen, garage, exterior). It may hold with nothing on the load side and trip the instant the load side is energized. The customer reports the old device "worked" (it was actually dead and passing power without protection, or had been mis-wired with the downstream conductors on the line terminals so nothing downstream was ever protected). A real ground fault, a damaged downstream conductor, moisture in a downstream device, or a crossed/grounded neutral is the second fault that the working device now reports. The dead branch the new GFCI feeds may be one outlet or a long string of receptacles, which changes how much circuit you have to bracket.

Quick checks

• Confirm line and load are landed correctly on the new GFCI; reversed line/load is a classic install error that mimics this.
• Press TEST/RESET with nothing downstream: a GFCI that holds isolated but trips with the load side connected points downstream.
• Disconnect the load-side conductors and reset; if it holds, the fault is downstream, not the device.
• Reconnect downstream sections one at a time, resetting after each, to bracket the leaking segment.
• Inspect downstream wet-location devices for moisture, corrosion, or a damaged conductor; check for a neutral that is grounded or shared.

Isolation tree

1. New GFCI holds with load-side wires off, trips when they are reconnected, no load plugged in? A standing ground fault in the downstream wiring or a downstream device: a hot-to-ground or neutral-to-ground path. The dead old device hid it.
2. Holds until a specific appliance is plugged in downstream? That appliance has internal leakage; the GFCI is catching its ground fault.
3. Downstream neutral grounded or shared with another circuit? A bonded or shared neutral on the load side creates a current imbalance the GFCI reads as leakage. Common where someone tied neutrals across circuits.
4. Trips only after rain or in a damp box outdoors? Moisture-driven leakage in a wet-location device; the old GFCI never reported it because it was not protecting.
5. New GFCI trips even with load-side fully disconnected? Recheck for reversed line/load or a faulty new device before chasing downstream.

Confirming diagnosis

With line/load verified, isolate the load side and reset to prove the device and line side are clean. Then reconnect the downstream run in sections, resetting after each, until the trip returns; the section that trips it holds the fault. On the suspect segment, de-energize and measure insulation resistance hot-to-ground and neutral-to-ground with a megohmmeter; a high-megohm reading is healthy, while a low reading (down into the kilohm range or less) confirms a leakage path. For an appliance, plug it into a known-good protected outlet to reproduce the trip and confirm the load, not the wiring, is leaking. For a shared or grounded neutral, lift the suspect neutral and confirm the trip clears, which proves the downstream neutral is bonded or crossed to another circuit. A clamp-style leakage meter around the load-side hot and neutral together reads the actual imbalance in milliamps and tells you whether you are near or well past the device threshold. Moisture is confirmed by drying the device with low heat and watching the trip clear, then return when re-wetted.

Remediation

Repair the downstream leakage at its source: replace a damaged conductor carrying a hot-to-ground path, dry out and reseal or replace a moisture-intruded wet-location device with an in-use cover where required, or remove/repair the appliance with internal leakage. Separate any downstream neutral that was grounded or shared so each circuit's neutral returns only its own current and is bonded only at the service, never at a downstream box. Correct a reversed line/load on the GFCI if found, landing the supply on LINE and the downstream feed on LOAD so downstream devices are actually protected. Re-energize, reset, and load each downstream outlet to confirm the GFCI holds under real use, including the wet-weather or appliance condition that exposed the fault. Verify with the GFCI's TEST button and a plug-in tester that protection is present at every downstream device. Document that the second fault pre-existed and was hidden by the failed original device, so the repair record reflects two distinct issues.

References

• National Electrical Code (NFPA 70), Article 210.8, Ground-Fault Circuit-Interrupter Protection for Personnel.
• NEC Article 250.6, Objectionable current over grounding conductors (shared/grounded neutrals).
• NEC Article 406.4(D), Replacement of receptacles (GFCI requirements).
• UL 943, Standard for Ground-Fault Circuit-Interrupters.
• NFPA 70E, Standard for Electrical Safety in the Workplace.