Open Ground Outlet: What the Tester Means and How to Fix It

An "open ground" light is the most common finding a plug-in tester turns up in an older house, and it means the outlet's safety ground goes nowhere.

Short answer: the receptacle's round ground hole isn't connected to an equipment grounding conductor. Most often it's a three-prong receptacle installed on an old two-wire circuit that never had a ground; sometimes it's a ground wire that's broken, disconnected, or stops at an unbonded metal box. The outlet still powers things, but a fault inside a metal-cased appliance can't trip the breaker. The NEC allows three fixes: run a real ground wire, install a GFCI labeled "No Equipment Ground," or put a two-prong receptacle back. Jumping the ground screw to the neutral is a bootleg ground and makes it worse.

What does "open ground" on an outlet tester mean?

A plug-in receptacle tester is three lamps across the three slots. One lamp sits between hot and neutral, one between hot and ground, one between neutral and ground. A correct outlet lights the hot-neutral and hot-ground lamps. Open ground lights only the hot-neutral lamp: the tester sees 120 V between the two flat slots and nothing between the hot slot and the ground hole. Match the pattern to the legend printed on the tester body; the lamp colors vary by brand.

What the tester can't tell you is why the ground is open, or whether a wire is dangling an inch from its screw. It also can't see a bootleg ground, which lights the "correct" pattern. That's covered in what is a bootleg ground.

Why does an outlet show open ground?

The first row is the common one. Houses wired before grounded receptacles became standard have cable with two conductors and no bare ground. Somewhere along the way, someone replaced the two-prong receptacles with three-prong ones so modern plugs would fit, and the ground hole was never connected to anything. The whole subject of ungrounded circuits, and what they mean for the house, is in two-prong outlets and ungrounded circuits. This guide stays on the reading and its fixes.

How to confirm an open ground

Start with the plug-in tester at every outlet in the house, not just the one that bothered you. The pattern across rooms tells you whether you have a wiring-era problem or a single bad connection.

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Then confirm with a multimeter set to AC volts. Keep the probes on the face of the receptacle; nothing here involves removing the cover plate.

A few stray volts between hot and ground on an open-ground outlet is the meter reading a floating pin through capacitance, not a weak ground. Any reading well under line voltage means there's no ground path. If hot-to-ground reads 120 V but the house is clearly old two-wire, suspect a jumper behind the receptacle: the multimeter can't tell a bootleg from a real ground either. Only a look inside the box, or a ground-impedance tester, settles that, and both are electrician work.

Is an open ground outlet dangerous?

The equipment grounding conductor does one thing: it gives fault current a low-resistance path back to the panel so the breaker trips fast (NEC 250.4(A)(3) and (A)(5)). If the hot wire inside a toaster oven, a desktop computer, or a window unit chafes against the metal case, a grounded outlet turns that into a tripped breaker. An open ground turns it into a live case waiting for the next hand.

Three consequences follow:

• Metal-cased appliances are the risk, not lamps or phone chargers. Anything with a three-prong plug has a case the manufacturer expected to be grounded.
• Surge protectors don't work. A surge strip diverts the surge to ground. With no ground there is nowhere to send it, and most strips light a "not grounded" or "protected" warning for exactly this reason. See power strips vs surge protectors.
• GFCI protection still works. A GFCI measures the imbalance between hot and neutral and needs no ground to trip. That's why it's one of the legal fixes.

The three fixes NEC 406.4(D)(2) allows

When a receptacle on a circuit with no equipment grounding conductor is replaced, the NEC gives three choices, and only three:

The ground-wire option is the only one that restores full protection, and 250.130(C) is more flexible than people expect: the new ground doesn't have to follow the circuit's cable. It can run to any accessible point on the grounding electrode system, the grounding electrode conductor, the ground bar in the panel feeding the circuit, or the grounded service conductor at the service. Where that's a short run through a basement or attic, it's often the cheapest real fix.

Under the GFCI option, 406.4(D)(2) also prohibits connecting a ground wire from the GFCI to any outlet it feeds downstream. The ground hole stays empty on purpose; the label tells the next person why.

Why a bootleg ground is not a fourth option

A jumper from the ground screw to the neutral screw makes the tester read "correct" and puts the neutral conductor on every metal case plugged in. If that neutral ever opens upstream, those cases sit at line voltage. The how and why is in what is a bootleg ground; the short version is that it violates NEC 250.24(A)(5) and 406.4(D)(2) and converts a missing safety layer into an active hazard.

Open ground on a home inspection

An inspector's receptacle tester finds open grounds in most houses from the ungrounded era, and the report will list each one. What the finding means depends on the fix in place:

• Three-prong receptacle, no ground, no GFCI, no label: a violation of 406.4(D)(2) and a legitimate repair item.
• GFCI with "No Equipment Ground" label: compliant. The tester still reads open ground, because there still isn't one; the label is the answer. An informed inspector notes it as such. See home electrical inspection before buying.
• Two-prong receptacles: compliant, though buyers often budget for GFCI replacements where they'll plug in computers and kitchen appliances.

If the inspection shows one open ground in an otherwise grounded house, that's a connection problem, and it's cheap to have an electrician open the box and fix it.

Why is this electrician work?

Confirming the reading is safe with the tester and multimeter on the face of the receptacle. Everything past that point means pulling the device out of the box with the circuit live or verifying it dead, deciding whether the armor or box is a lawful ground path (NEC 250.118), and landing conductors correctly. Running a ground under 250.130(C) means working at the panel or the grounding electrode. A licensed electrician handles that, and in many jurisdictions the receptacle replacement itself needs a permit; see electrical work homeowners can legally do.

Standards and code reference

The standards behind this guide, for looking up in the edition your jurisdiction has adopted:

• NEC 406.4(D)(1): grounding-type receptacles require an equipment grounding conductor, or a 250.130(C) extension
• NEC 406.4(D)(2): replacement options where no equipment grounding conductor exists: non-grounding receptacle, GFCI receptacle, or GFCI-protected receptacles, with the "No Equipment Ground" and "GFCI Protected" markings
• NEC 250.130(C): permitted connection points for an equipment grounding conductor added to an existing ungrounded branch circuit
• NEC 250.4(A)(3) and (A)(5): purpose of equipment grounding and the effective ground-fault current path
• NEC 250.118: wiring methods that qualify as equipment grounding conductors, including listed armored cable
• NEC 250.146: bonding a receptacle to a grounded metal box
• NEC 250.24(A)(5): no grounded-conductor-to-ground connection on the load side of the service
• NEC 110.3(B): installing listed equipment per its instructions, including the tester's own limits

Code editions and local amendments vary. Confirm the adopted edition with your AHJ, and treat manufacturer instructions as governing wherever they are more restrictive.

Where to go next

• The bigger picture: two-prong outlets and ungrounded circuits
• The tester reads "correct" but shouldn't: what is a bootleg ground
• Hot and neutral swapped instead: reverse polarity outlet
• Grounding vs bonding
• Adding circuits while the electrician is there? Check capacity with the home electrical load calculator

More in our wiring and home electrical safety guides.