How to check whether your outlet is grounded

A plug-in tester takes seconds and tells you whether the outlet by your bed has a working ground port. Here is how to read it, and when to call an electrician.

October 9, 2026 6 min read

Most bedrooms have an outlet within reach of the bed, and most people have never wondered what is behind it. If you use a grounding sheet, it is worth a minute of your time. The cord plugs into only one of the three openings, the round ground port, and that port is only useful if it is actually connected to your home's grounding system. A plug-in outlet tester, the small yellow device sold at every hardware store, will tell you in seconds.

Key points

A grounding cord uses only the round ground port, which works only if it connects to your home's grounding system.
A plug-in tester shows faults like open ground, but can't confirm ground quality or catch every miswiring.
Two-prong outlets, cheater adapters and GFCIs marked "No Equipment Ground" give a grounding cord no ground path.
Don't fix wiring yourself; try another outlet, and contact a licensed electrician if none read correct.

Why the ground port is the only part that matters

A standard US outlet has three openings. The two flat slots carry power: the shorter one is "hot" and the taller one is "neutral." The round hole below them is the ground, a separate safety path that normally carries no current at all. In a correctly wired outlet, that path runs back through the wiring to your electrical panel and on to the earth.

A grounding cord, like the one on the Equilibrium Grounding Fitted Sheet, uses only that round port. It does not draw power from the outlet. But if the ground behind the faceplate is missing or disconnected, the cord is plugged into nothing. You can't see this from the outside, which is why a plug-in outlet tester is worth the few dollars. The tester that comes with Equilibrium products checks that the fabric conducts; it doesn't test the outlet.

How a plug-in tester works

A standard three-prong receptacle tester has small lights wired between its prongs. Each light glows when there is voltage between a particular pair of contacts, such as hot and neutral, or hot and ground. The combination of lights that come on tells you which connections are present and which are missing or swapped.

To use one, plug it into the outlet with the round pin in the ground port, then compare the lights with the key printed on the tester's body. Klein Tools' instructions for its RT100 tester suggest first checking the tester on an outlet you know is wired correctly, so you know the tester itself works.

What the common light patterns mean

Testers from Klein, Sperry and others check for the same set of conditions. The exact color and position of the lights differ between brands, so the key on your own tester is the final word. On most common three-light testers, the patterns look like this:

Reading	What it means	Typical pattern
Correct	Hot, neutral and ground are all connected in the right places.	Two lights on, usually yellow or amber, with the red light off
Open ground	The ground contact isn't connected. A grounding cord will not work here.	A single light on
Open neutral	The neutral contact isn't connected.	Varies by model; check the key
Open hot	The hot contact isn't connected, so the outlet has no power.	No lights
Hot/neutral reversed	The hot and neutral wires are swapped (often called reversed polarity).	Varies by model, often includes the red light
Hot/ground reversed	The hot and ground wires are swapped. This is a hazardous condition.	Varies by model, often includes the red light

Anything other than "correct" is a wiring problem. Both Klein and Sperry tell users to consult a qualified electrician if the tester shows a fault. If you see a hot/ground reversed reading in particular, don't plug anything into that outlet until an electrician has looked at it.

What a tester can't tell you

These testers are useful, but they are simple. Klein's own manual notes that its tester does not indicate the quality of the ground connection, combinations of defects, or a reversal of the neutral and ground wires. Mike Twitty, a licensed electrician and former home inspector, has written that a "bootleg ground," where someone has jumped the ground terminal to the neutral, can make a miswired outlet read as correct. A dim light can point to a loose connection.

In other words, a "correct" reading is a good sign, not a guarantee. If your home has had amateur electrical work, or you simply want certainty, an electrician can test the outlet with proper equipment.

Two-prong outlets and "cheater" adapters

Outlets with only two slots have no ground port, and in most cases no ground wire in the box behind them. They are common in older homes. Accounts from electricians date the general National Electrical Code requirement for grounding-type receptacles to the 1962 edition, though earlier rules covered some locations, such as laundry areas, and local adoption varied.

A three-to-two-prong adapter, sometimes called a cheater plug, does not fix this. The adapter's small metal tab is meant to attach to the faceplate screw, and it only provides a ground if that screw and the metal box behind it are themselves grounded, which in many older homes they are not. A consumer guide from the Electrical Safety Foundation (ESFI) says three-prong adapters are not safe because they are not properly grounded. A grounding cord plugged into one of these adapters is almost certainly not connected to ground.

In other words, a "correct" reading is a good sign, not a guarantee.

GFCI outlets

GFCI outlets, the kind with "Test" and "Reset" buttons, are designed to cut power quickly when they detect current leaking where it shouldn't. They are common in kitchens and bathrooms, and they are sometimes used as an approved replacement for old two-prong outlets.

That second case matters. Under the National Electrical Code, a GFCI can be installed where there is no ground wire, as long as it is marked "No Equipment Ground." It offers shock protection, but it does not create a ground. If you see that label on an outlet, or on outlets downstream of a GFCI, a grounding cord plugged in there has no ground path. A GFCI that is properly grounded works the same as any other grounded outlet for a grounding cord.

One more quirk: the GFCI button on many plug-in testers needs a working ground to trip the outlet, so on an ungrounded GFCI it may do nothing. Use the outlet's own "Test" button instead to check that the GFCI itself is working.

If your outlet isn't grounded

If the tester shows open ground, or any other fault, don't try to fix the wiring yourself. Try a different outlet nearby. With a 15-foot cord, the Equilibrium sheet can usually reach more than one, and it is worth testing each candidate. If none of the outlets near your bed read as correct, contact a licensed electrician. They can tell you whether a ground is available and what the options are for your home.

It is also worth re-testing after any electrical work, a move, or rearranging the bedroom.

Check the cord, too

A good outlet is only half of the connection. Every so often, look over the grounding cord from end to end. Make sure the plug sits firmly in the outlet and the other end is fully seated where it connects to the sheet. Look for kinks, cracks, crushed spots where a bed leg has rested on it, or damage from pets. Route the cord where it won't be pinched between the mattress and the wall.

If the cord is damaged, stop using it and replace it. Velin sells a replacement grounding cord separately. For keeping the sheet itself in good condition, see our care guides and our article on washing grounding sheets without losing conductivity.

A minute with a tester, a quick look at the cord, and a call to an electrician if something looks wrong: that is the whole routine. If you have broader questions about electrical safety and grounding products, we cover them in Are grounding sheets safe?.

From the Equilibrium collectionEquilibrium Replacement Grounding CordSold separately to replace a grounding cord that is cracked, crushed, kinked or otherwise damaged.View product