Neutral-to-Ground Reads High Voltage: Floating vs Load Decision Tree

Why this matters

A neutral-to-ground voltage reading is normally a small number: a few volts or less, reflecting the IR drop on a loaded neutral. When that reading is high (tens of volts, or worse, near line voltage) something is wrong with the system's grounded-conductor path, and the two main causes are very different in danger. A high but modest neutral-to-ground reading under load can mean a loaded neutral with excessive impedance. A neutral-to-ground reading near full line voltage usually means the neutral is open or floating, or the ground reference is lost, so the neutral has risen to source potential and the equipment-grounding system may be energized. The distinction (a genuinely floating/open neutral versus normal-but-elevated load drop versus a lost ground) decides whether you have a nuisance or a shock-hazard emergency. Read it correctly before touching anything bonded.

Symptom presentation

Measured neutral-to-ground (N-G) voltage is higher than expected. In the benign case it reads a few volts and climbs modestly with load (normal neutral IR drop). In the alarming case it reads a large fraction of line voltage, may be roughly stable regardless of local load, and the equipment-grounding conductors or metal enclosures may show voltage to a true earth/known ground. The customer may report shocks from appliances, tingling on metal surfaces, or erratic equipment. Other symptoms of an open service neutral (see-sawing 120 V legs, lights brightening/dimming) may accompany it.

Quick checks

• Magnitude. A few volts N-G under load is normal. Tens of volts to near line voltage is a fault; treat anything substantial as a hazard until proven otherwise.
• Does it track load? A small N-G that grows with neutral current is normal IR drop. A large N-G that does not depend on local load points to an open/floating neutral or lost ground.
• Reference against true earth. Read the equipment ground and neutral against an independent known-good earth reference; if the "ground" itself is elevated, the bonding/grounding path is compromised.
• Check the main bonding jumper. Confirm neutral and ground are bonded at the service (and only there) and the main bonding jumper is intact.
• Look upstream. Open-neutral symptoms (see-saw legs) plus high N-G point at a service-neutral problem.

Isolation tree

1. Is the reading normal or a fault? Small N-G that rises with load and falls to near zero with load off is normal neutral drop, no fault. Large or load-independent N-G is a fault; proceed carefully.
2. Floating/open neutral? If N-G is large and the 120 V legs see-saw under load (one rises, one sags), the neutral is open upstream. The neutral floats toward line potential and energizes everything referenced to it. Bound the open: at the panel, meter, or in the utility drop (this overlaps the open-neutral diagnosis). This is a hazard.
3. Lost or high-impedance ground reference? If N-G is high but legs are balanced, suspect a missing or high-resistance grounding-electrode/bonding path so the ground reference has drifted. Verify the main bonding jumper, grounding-electrode conductor, and electrode connections. A lost ground can leave enclosures elevated.
4. Improper neutral-ground bond downstream (or missing bond). Neutral and ground must bond only at the service. A missing service bond, or extra/wrong downstream bonds, distorts N-G readings and can create hazardous paths. Verify the bond exists at the service and nowhere it should not.
5. Bootleg/swapped wiring at a device. A miswired device can put load current on the ground or swap neutral and ground locally, producing odd N-G readings at that outlet. Isolate by testing at the panel versus at the device.

Confirming diagnosis

Confirm by separating "floating" from "loaded" with two tests. First, reference against a true independent earth: if both neutral and the equipment ground read high to real earth, the system's grounded/grounding path is compromised (open neutral or lost ground), a hazard. Second, watch load dependence and leg balance: an open neutral see-saws the legs and the N-G voltage is large and source-driven, while a benign loaded-neutral reading is small and tracks neutral current. Restoring the suspect connection (re-bonding, repairing the neutral, or fixing the electrode path) and watching N-G fall to a few volts under load, with balanced legs and a grounded system referenced to earth, confirms the fix. Never conclude "just load drop" on a large reading without proving the neutral and ground paths to earth are intact.

Remediation

• Open/floating service neutral: locate and repair the open (panel/meter is contractor work; utility drop/lateral is the utility's). Until repaired, the system is hazardous; advise limiting loads and treat metal as potentially energized.
• Lost/high-impedance ground or missing main bond: repair the grounding-electrode conductor, electrode connections, and the main bonding jumper at the service per code; re-test N-G.
• Improper downstream neutral-ground bond: remove neutral-ground bonds downstream of the service; bond only at the service equipment.
• Bootleg/miswired device: correct the device wiring so the ground carries no normal current and neutral/ground are not swapped.
• Confirm with N-G near zero under load, balanced legs, and a verified earth reference.

References

• NFPA 70 (National Electrical Code) Article 250 (grounding and bonding), including the single neutral-ground bond at the service (250.24, 250.28) and prohibition of downstream neutral-ground bonds.
• NEC Article 200 for grounded-conductor (neutral) use and identification, and Article 230 for services.
• NFPA 70E for energized-work safety and verification of de-energization.
• Local utility service rules defining the demarcation for service-neutral repairs.