Bootleg Ground Versus True Ground On An Old Receptacle Decision Tree

Why this matters

A three-prong receptacle in an older home that passes a plug-in tester can still be a bootleg ground: a jumper from the neutral to the ground terminal that fakes a ground reference. The tester lights up correct because it sees continuity between neutral and ground, but there is no actual equipment grounding conductor (EGC) back to the panel. This is dangerous in three ways: under load the bootleg jumper puts normal neutral voltage on the equipment ground and every connected chassis, an open neutral upstream energizes those chassis to full line potential, and the receptacle gives surge and fault current nowhere safe to go. The plug-in tester is blind to it, so a tech who trusts the green lights certifies a hazard. This tree separates a real EGC from a bootleg and from a true open ground.

Symptom presentation

The scenario is a pre-1960s home with two-wire NM (no ground) that has three-prong receptacles, or a home inspector flagging a receptacle that tests grounded but the wiring method has no ground. Ask whether the receptacles were upgraded from two-prong, whether GFCI protection was added (the legitimate retrofit path), and whether anyone has reported tingles on appliance cases. A receptacle that reads grounded on a plug-in tester but lives on two-wire cable is a bootleg until proven otherwise.

Quick checks before isolation

A plug-in tester alone cannot tell a bootleg from a true ground; you need a meter. Read hot-to-ground and hot-to-neutral voltage: on a true ground both read ~120V and the small difference reflects only conductor drop. On a bootleg, hot-to-ground tracks hot-to-neutral exactly because ground IS neutral. The decisive test is to apply a load on the circuit and read neutral-to-ground voltage: a true ground holds neutral-to-ground near 0V regardless of load; a bootleg shows neutral-to-ground rising under load only if the jumper is at a different point, but a direct device-level bootleg reads 0V always - so the open the box and inspect step is required to confirm.

Isolation tree

Step 1 - Identify the wiring method. Open the receptacle and look at the cable. Two-wire NM (black, white, no bare ground) or two-wire armored cable with a three-prong device installed is the bootleg setup. If you find a true EGC (bare or green) landed on the ground screw and continuous back to the panel, it may be a real ground - go to Step 2 to confirm continuity. If the only thing on the ground screw is a jumper from the neutral terminal, it is a bootleg - go to Step 3.

Step 2 - Confirm a real EGC. With the circuit de-energized, measure resistance from the receptacle ground screw to the panel ground bar; a true EGC reads near 0 ohms. Energize and apply load; neutral-to-ground stays near 0V and the EGC carries no current (clamp it - a true EGC reads ~0A under normal load). If continuity is good and the EGC carries no normal current, it is a true ground. If the ground screw shows continuity to the panel only through the neutral, it is a disguised bootleg.

Step 3 - Confirm the bootleg. The jumper from neutral to ground at the device, or a neutral landed on the ground screw, is the bootleg. Under load this places neutral drop voltage on the equipment ground; reverse the line and neutral on a bootleg-grounded outlet and a plug-in tester will alarm in a way a true ground never does (a known field tell). Remove the jumper and the ground terminal goes dead, confirming there is no real EGC.

Step 4 - Rule out a plain open ground. If there is no jumper and no EGC, the receptacle is simply ungrounded (open ground) - which is honest but still non-compliant for a three-prong device without GFCI. Distinguish from bootleg: open ground reads infinite ground continuity and 0V hot-to-ground; bootleg reads continuity through neutral and ~120V hot-to-ground.

Confirming the diagnosis

A confirmed true ground reads near 0 ohms ground-to-panel, near 0V neutral-to-ground under load, and ~0A on the EGC. A confirmed bootleg shows the ground terminal fed only by a neutral jumper, the ground terminal going dead when the jumper is removed, and (the classic tell) a reverse-polarity tester reading that flips abnormally because hot and ground swap behaves differently than on a real ground. A confirmed open ground has no EGC, no jumper, and an isolated ground terminal.

Remediation

Remove every bootleg jumper - it is prohibited and dangerous. The compliant retrofits for ungrounded receptacles under NEC 406.4(D) are: replace with a true grounded receptacle only if a real EGC is run; install a GFCI receptacle (or GFCI-protect the circuit) and label it No Equipment Ground; or replace with a two-prong receptacle. A GFCI provides personnel protection without an EGC, which is why it is the standard fix for ungrounded circuits. Do not leave a three-prong device on an ungrounded circuit without GFCI protection and the required No Equipment Ground label.

References

• NEC 2023 Article 406.4(D) - Replacement of receptacles, grounded and GFCI options
• NEC 2023 Article 250.114 - Equipment required to be grounded
• NEC 2023 Article 250.146 - Connecting receptacle grounding terminal to box/EGC
• NEC 2023 Article 406.3(D) - No Equipment Ground labeling
• UL 943 - Ground-Fault Circuit-Interrupters (basis for the ungrounded-circuit GFCI retrofit)