A cheater plug is a small adapter that lets you plug a three-prong electrical cord into an older two-slot outlet. It’s officially called a three-prong-to-two-prong adapter or AC ground lifter, but it earned the nickname “cheater plug” because it bypasses the grounding protection that the third prong provides. They cost about a dollar at any hardware store, and millions of people use them in older homes that were never wired with grounded outlets. While they’re legal to sell and technically have a safe use case, most people use them incorrectly, which creates real electrical hazard.
How a Cheater Plug Works
The adapter has two flat prongs on one side that fit into a standard two-slot outlet. On the other side, it has two slots and a round hole that accept a three-prong plug. The key feature is a small metal tab (or sometimes a short green wire on older models) hanging from the bottom of the adapter. That tab is the ground connection, and it’s designed to be secured under the screw that holds the outlet’s faceplate in place.
The idea is straightforward: in many older homes, the metal outlet box is connected to the building’s grounding system through metal conduit, even though the outlet itself only has two slots. By screwing that metal tab to the faceplate screw, you’re supposed to create a path from the adapter’s ground contact, through the screw, into the metal box, and down to earth ground. Modern cheater plugs use a flat tab instead of a flexible wire to reduce the chance of accidentally connecting it to the wrong spot. They’re also polarized, with one blade wider than the other, so you can’t reverse the hot and neutral connections. Many versions include a small bump on top that physically blocks you from inserting a three-prong plug the wrong way around.
Why the Third Prong Matters
The third prong on a plug is the ground pin. It exists to protect you from electrical shock if something goes wrong inside an appliance. In normal operation, electricity flows through the hot wire, powers the device, and returns through the neutral wire. The ground wire just sits there doing nothing. But if a wire comes loose inside the appliance and touches the metal housing, the ground wire gives that stray current a safe path back to the electrical panel, where it trips the breaker and shuts everything off.
Without that ground path, the metal case of the appliance stays energized. It sits there waiting for you to touch it while also touching something grounded, like a water pipe, a wet floor, or a radiator. When that happens, you become the path to ground, and current flows through your body. Grounded outlets have been required in new construction since 1962 precisely because of this risk.
When the Adapter Actually Works Safely
A cheater plug does its job only when two conditions are met: the metal tab is attached to the faceplate screw, and that screw connects to a properly grounded metal outlet box. In homes built with metal conduit running back to the electrical panel, the box itself often provides a ground path even though nobody installed a three-slot outlet. In that situation, the adapter with its tab secured is genuinely completing the ground circuit.
You can verify whether your metal outlet box is grounded using a basic voltmeter. With the power on, touch one probe to the metal box and the other to the hot (black) wire slot. If you read approximately 120 volts, the box has a ground path. If the reading is much lower, the box is not reliably grounded and the adapter won’t protect you regardless of whether you attach the tab.
In practice, most people never attach the tab. They just push the adapter into the wall and plug in their device, which completely eliminates the ground connection. At that point, the adapter is doing exactly what its nickname suggests: cheating the safety system.
Appliances That Pose the Highest Risk
Any appliance with a metal exterior is more dangerous without a proper ground. Think space heaters, toasters, power tools, desktop computers, and older refrigerators. If an internal wire fails in one of these devices and there’s no ground path, the entire metal body can become electrified. You wouldn’t know until you touched it.
High-draw appliances also increase the risk simply because more current is available to flow through your body in a fault. A standard wall outlet is rated for 15 amps, and most plugged-in devices draw well under 13 amps. The danger isn’t overloading the circuit; it’s that when a fault occurs in a powerful appliance, the consequences are more severe and faster.
Double-insulated tools and devices (the ones with only two prongs to begin with) don’t need a ground connection. Their plastic housings and internal insulation provide protection. If your device came with a two-prong plug, it was designed to be safe without grounding. If it came with three prongs, the manufacturer determined it needs that ground path.
What the Electrical Code Says
The National Electrical Code doesn’t ban cheater plugs outright, but it effectively makes them unnecessary by providing three approved options for dealing with old two-slot outlets. If a ground wire exists in the outlet box but was never connected, the code requires that any replacement outlet be a grounding type with the ground terminal properly wired. If no ground wire exists, you have three choices under NEC section 406.4(D)(2):
- Replace with another two-slot outlet. This is code-compliant but doesn’t solve the problem of plugging in three-prong devices.
- Install a GFCI outlet. A ground-fault circuit interrupter doesn’t provide equipment grounding, but it detects when current is leaking (such as through your body) and cuts power in milliseconds. The outlet and its cover plate must be labeled “No Equipment Ground.”
- Install standard three-slot outlets protected by an upstream GFCI. You can put a GFCI outlet or breaker at the start of the circuit and then use regular three-prong outlets downstream. Each one must be labeled “GFCI Protected” and “No Equipment Ground.”
The GFCI option is the most practical solution for most older homes. It gives you three-slot outlets throughout the house, protects against electrical shock even without a true ground wire, and costs relatively little. A GFCI device works by constantly comparing the current flowing out on the hot wire with the current returning on the neutral wire. If even a tiny amount goes missing (as little as 4 to 6 milliamps, which means some current is escaping through an unintended path), it trips in a fraction of a second. It doesn’t need a ground wire to do this.
Why Electricians Call Them Dangerous
The core problem with cheater plugs isn’t the adapter itself. It’s human behavior. The tab rarely gets connected. Even when it does, most homeowners have no way to verify that the outlet box is actually grounded. And the adapter gives a false sense of security: you see a three-prong plug seated in the wall and assume everything is properly connected, when in reality your expensive appliance has no more shock protection than if you’d cut the ground prong off with pliers.
Home inspectors flag cheater plugs as a safety concern during inspections. The InterNACHI inspection standards specifically list them alongside other dangerous modifications to ungrounded outlets, noting that while they’re cheaper than proper rewiring, they provide less protection than any of the code-approved alternatives. For the cost of a single GFCI outlet (typically $15 to $25) and a few minutes of work, you can eliminate the need for every cheater plug on that circuit.