What Are Those Buttons Between Wall Sockets?

Brow Beat
Slate's Culture Blog
Aug. 20 2012 8:45 AM

What’s That Thing? Wall Socket Edition

testswitch

Juliana Jimenez for Slate

Once again we’re trying to dispel a modern mystery that lurks in plain sight. For previous columns, click here; to submit your own suggestions, see the e-mail address below.

Among the many good reasons to watch the TV series Six Feet Under were the grisly, sometimes funny, and occasionally moving death scenes that opened nearly every episode. As the series seemed to enjoy demonstrating, there are lots of ways to go. Who by fire, as Leonard Cohen wondered? Who by “something blunt”? And who, in Season 1, Episode 5, by bathtub electrocution?

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Who indeed? Next time you’re in your bathroom, have a look at the electrical sockets. It’s very likely there are two buttons between the two plug insertion points, one labeled “TEST” and the other “RESET.” What do they do? Are you supposed to be testing your wall socket?

As always, a few guesses:

a) They’re a safety device aimed at preventing the use of long cords—especially extension cords—which would increase the likelihood of a device getting near water. AC power is “alternating current,” which means the flow of electricity is regularly reversed. These outlets sense the length of the cord by timing the reversals, and they cut off power if a cord is too long. Test quarterly.

b) The buttons are a government-mandated child-safety feature that almost no one understands, according to Kealie Williams of the Consumer Electrical Products Board, a trade group. To keep kids safe from hair-dryer/water-type calamities, turn off the outlet by pressing both switches simultaneously. The outlet is shut off until the buttons are pressed again in a specific order: TEST, RESET. No need to test, because the button doesn’t test anything.

c) They’re a safety feature, but, as Leonard Cohen surmised, the threat is fire, not water. Circuit breakers in your home—in your basement, probably—are designed to trip (i.e., shut off power) if their load becomes too heavy. But if a device falls in water, the circuit breaker itself may overheat, causing a fire wherever your circuit breakers are. Test every year.

d) The outlets are a mandatory safety device that almost noone understands (and that Six Feet Under writers apparently weren’t too worried about, either). If too much power is flowing through an outlet—say, because a device has fallen into water—the power is automatically cut off, and the RESET button pops out. Test monthly.

And the answer is…

d) The switches are called GFCIs: Ground Fault Circuit Interrupters. Confused? Me too. So I talked to John Drengenberg, the Consumer Safety Director for Underwriters Laboratories, the folks who for more than a century have been checking the safety of nearly everything in your house that could kill you. (In an average home, about 125 devices carry a “UL” seal of approval.)

How do GFCIs work? If you drop an appliance (like a hair dryer) into water (say, in a tub), things head south quickly. Electricity surges into the water and down the drain pipe like lightning seeking ground. If you’re in the tub, your heart can go into fatal fibrillation. (Drengenberg, whose job it is to think about such things, notes that human blood is a particularly fine electrical conductor.) As mentioned above, the flow of AC (alternating current) power is constantly being reversed. The clever GFCI checks that the flow of power out of a device matches the flow going in. If the power isn’t coming back, then it’s going somewhere bad—in which case the GFCI cuts off the power.

According to Drengenberg, GFCIs have been around for about twenty years now. In the U.S., they were first mandated in bathrooms. Now, in most municipalities, they’re obligatory in kitchens, garages, outdoor and swimming pool areas, and even basement outlets. (They’re mandated when you build new or extensively renovate.)

A GFCI is not like a circuit breaker, which is designed to prevent fire and which works so slowly that it would never activate in time to prevent an electric shock injury. A GFCI, in contrast, reacts in 20-25 milliseconds, well before your heart would have a chance to go bananas.

Why the push to install them in other settings? Because shocking things can happen outside the bathroom, too. Say you’re walking in wet grass in bare feet, plug in an electric lawnmower, and accidentally touch the prong of the plug. Bad news.

Because many older homes don’t have GFCIs installed, UL-approved hair driers have their own GFCI built into the plug. In Europe, where voltages are roughly double America’s, there are countries, like the United Kingdom, that don’t permit any outlets in the bathroom, except the occasional very low power outlet to charge things like shavers. So you have to go to another country—or at least another room—to dry your hair.

Should you be regularly testing the TEST button? Yes! At least once a month. Drengenberg suggests combining it with your monthly check of your fire smoke alarms. Press TEST, and the RESET button should pop out. If it does, the GFCI is working and you can press the RESET button back down. If the RESET button doesn’t pop out, or can’t be put back in, then call an electrician.

Bonus fact: When you press TEST, the RESET button pops out so fast that it looks like the reset button is popped by the force of the test switch being pressed. But there’s no mechanical link between them: It’s just that the GFCI works really, really fast. (And fast, of course, means safe.)

Bonus question: As a child I saw a movie or show, possibly while staying up and watching bad late-night TV, which featured a murder by electrocution. A woman is relaxing in a bathtub when a surreptitiously trained pet monkey runs in, grabs the hair dryer, and throws it into the tub. (There were no GFCIs back then.) If this rings a bell, drop a link in the comments, because I really hope I did not make that monkey up.

And of course if you spot anything else you’re wondering about—in the kitchen, bathroom, or anywhere else for that matter—send a pic and description to whatisthat@markvr.com.

Update: The answer given as correct, option d), mischaracterizes what activates the GFCI. As explained later in the piece, the GFCI reacts to a difference between what’s going in and what’s going out—so a GFCI trips when too much power flows through in relation to how much is returning, not because of a net increase in power flow. Thanks to commenters Arlington and Finneus for pointing this out.

Mark Vanhoenacker is a writer in New York. Follow him on Twitter.

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