Ground Tests Fine But Shocks Persist: A Misleading-Reading Decision Tree

Why this matters

A receptacle tester shows a correct ground, a continuity check from the equipment ground to the panel reads near zero ohms, yet a customer keeps reporting a tingle off an appliance, a pool ladder, or a metal sink. The ground "tests fine," so the obvious conclusion is that the customer is imagining it or the appliance is faulty. People die from this assumption. A ground that passes a static continuity test can still leave a dangerous touch voltage on a surface, because continuity to the panel is not the same as an effective, low-impedance bonding path that holds every accessible metal part at the same potential under fault and under normal stray current. This is one of the few electrical complaints where a wrong call is lethal.

Why the good reading misleads

A standard ground test answers one question: is the equipment ground conductor (EGC) electrically connected back to the panel? It does not answer whether that conductor can clear a fault fast enough, whether the neutral and ground are improperly bonded downstream, whether a bootleg ground is jumpered to neutral at the device, or whether stray current from the utility neutral or a pool bonding deficiency is raising the potential of everything the customer touches.

The single-point continuity reading also misses voltage that appears only under load. A shared neutral carrying unbalanced current, an open utility neutral, or a neutral-to-ground bond in the wrong place will put several volts on grounded surfaces only while current flows. Measured at rest with no load, the ground looks perfect. The shock happens under load. That is the path versus single-point trap in its most dangerous form.

Symptom presentation

• Repeated mild shocks or tingles from a grounded metal surface, often worse when an appliance runs.
• A pool, spa, or wet-location complaint where bonding is involved.
• Receptacle tester shows correct wiring and the EGC reads continuous to the panel.
• Measured neutral-to-ground voltage is higher than a few hundred millivolts, especially under load.
• The tingle changes with which loads are running, or worsens during utility-side events.

Quick checks

• Measure voltage from the complained-of surface to a known remote earth reference and to the system ground, both at rest and with major loads running. A persistent reading above roughly 1 to 2 volts on an accessible surface is a real hazard to investigate, not noise.
• Measure neutral-to-ground voltage at the receptacle. A few hundred millivolts is normal load-driven drop. Several volts indicates an open neutral, a downstream N-G bond, or a bootleg ground.
• Confirm the EGC is a true ground, not a jumper from neutral at the device (a bootleg ground). A bootleg ground passes a 3-light tester perfectly while energizing the device case if hot and neutral are ever reversed or the neutral opens.

Isolation tree

1. N-G voltage normal at rest, rises sharply under load. Suspect an open or high-resistance neutral, or current diverted onto the EGC. Read voltage across the neutral path under load to find the open point.

2. N-G voltage present even at rest, several volts. Suspect an improper neutral-to-ground bond downstream of the service (a subpanel with neutral and ground tied, or a bootleg ground). Separate neutrals and grounds at every panel except the service disconnect per NEC 250.24 and 250.142.

3. Surface voltage present, EGC continuity good, no N-G fault found. Suspect utility-side stray voltage (open or high-resistance utility neutral) or, at pools and wet locations, a bonding-grid deficiency. Measure between the surface and a remote earth electrode; utility-side issues persist with the main off.

4. Shock only at a pool, spa, or wet location. This is an equipotential bonding problem, not a fault. Verify the bonding grid ties all metal parts, the perimeter, and the water per NEC 680. A measurable potential between two accessible surfaces means the bond is incomplete or broken.

Confirming diagnosis

The confirming test depends on the branch. For a downstream N-G bond, lifting the suspect bond drops the surface voltage to near zero. For an open neutral, repairing the neutral termination restores normal N-G voltage and the touch potential disappears. For a bootleg ground, opening the device reveals the neutral-to-ground jumper, and replacing it with a true EGC or a GFCI device per NEC 406.4(D) resolves it. For utility-side stray voltage, the potential remains with the building main open, which points the investigation to the utility neutral and warrants a utility callout.

Remediation

• Repair or re-terminate an open or high-resistance neutral; restore the single service-point N-G bond and remove every downstream bond.
• Replace bootleg grounds with a proper EGC, or where no ground exists, a GFCI-protected device labeled per NEC 406.4(D).
• Restore or complete equipotential bonding at pools and wet locations per NEC 680.
• For persistent surface voltage with the main open, escalate to the utility for a neutral integrity check.

References

• NFPA 70, National Electrical Code, Article 250.24 and 250.142 (grounding and neutral-to-ground bonding location).
• NFPA 70, National Electrical Code, Article 406.4(D) (replacement receptacles, GFCI where no ground).
• NFPA 70, National Electrical Code, Article 680 (swimming pools, spas, equipotential bonding).
• NFPA 70E, Standard for Electrical Safety in the Workplace (energized measurement and shock-protection boundaries).