Troubleshooting Outlets And Switches
May 1, 2006
When something electrical doesn't work, it's so tempting to leap to difficult solutions: it must be a bad switch; or better yet, the motor's probably burned out. But why not start with the easy questions: “Is the thing plugged in?” “Is the switch turned on?” I know this is simple stuff that any idiot can figure out. But so often we become the idiot by not checking “Is it turned on?” and “Does it have power?”
A few years ago I woke up to a cold house. I leaped to the dramatic conclusion that I had a bad gas valve. I spent all day looking for the right replacement, only to find out when I went to remove the “bad” valve that the switch was in the “off” position. I'll never know how it got turned off. But turning it on sure solved the problem.
But never mind the gas valve. Let's think about ordinary wall outlets. What if you have power, the switch is turned on, and whatever you plugged in still doesn't work? Give in and do the easy thing - plug it into a different outlet. And if it still doesn't work? Then ask whether or not everything else in the house or building is working. If nothing else is, or half is, you may have a power outage from the utility. It's odd how big a relief it is to learn that no one around you has power either. It's more than “misery loves company.” The crisis of “Oh, no, I've got a problem” suddenly changes into “Those guys at the utility have a problem.”
If the buildings around you have power and you don't, the next place to go is your service panel. That's the circuit breaker box or fuse box. Before touching it, listen first for a sizzling noise. If there is, stay away and call an electrician. Otherwise, open the box and look for any circuit breaker that's “off,” or a damaged or loose fuse. Turn the circuit breaker on or replace the fuse with one of the same amperage.
By the way, circuit breakers and fuses are just switches. A fuse is a one-time switch. Use it once and throw it away like a paper cup.
Testing A Wall Outlet
Let's say you've done all of the above and you're pretty sure you have a bad outlet. The simplest way to test an outlet is to plug in something that you know will work if there's power, but we've already done that, right? You can do basic troubleshooting with just a few inexpensive tools that are available at hardware stores. Some of these are a three-prong outlet analyzer, a neon tester, a continuity tester, a pen-type mini-voltmeter and a multi-meter.
An ordinary outlet is sometimes called a duplex - like a duplex house. That word duplex is a clue - the top and the bottom aren't always the same. Especially in a kitchen, the two outlets can have two different fuses or circuit breakers. Never assume that if one doesn't have power that the other doesn't.
Here's another thing you know perfectly well but may forget in the excitement of troubleshooting. An outlet is sometimes turned on and off with a wall switch. Make sure the wall switch is on. And with a duplex, one outlet may be switched and the other not.
Testing A Three-Slot (With Grounding Slot) Outlet
The easiest way to test a three-slot outlet is with a three-prong outlet analyzer (see Figure 1). You don't have to take anything apart. You simply plug the analyzer into the outlet. A combination of lights tells you if the hot, neutral and grounding wires are connected correctly, are not connected, or if they're reversed.
You can also test a socket with a neon tester, a multi-meter, or a pen-type voltmeter. Whichever you use, make sure that you touch only the insulated part of the device's probes, never the metal tips. Touching bare metal can always be dangerous, and at the least not feel very good.
If you're using a multi-meter, turn it on to the “volts AC” setting for the highest voltage. Volts AC may be indicated by a V with a squiggle above it.
To test for power with any of these tools, put one probe in the short (hot) slot of the outlet and the other in the long (neutral) slot. The neon tester should glow. A voltmeter or multi-meter should give a reading around 120V, plus or minus a few volts. If you see nothing, there's no power at the outlet. That means that either the power is shut off at the service panel, the outlet is defective, or there is a switch, perhaps a wall switch, that is off.
To test for polarity, put one probe in the short (hot) slot of the outlet. Put the other probe in the grounding slot. You should see a glow, or a reading. If not, put one probe in the long (neutral) slot and the other in ground. If you get a glow or reading, it means that hot and neutral are reversed inside the outlet.
To test for grounding, with the probes positioned as for testing polarity, if the device doesn't glow at all, the outlet isn't grounded. That's possible even if there's a grounding slot in the outlet. Someone could have replaced an old nongrounded outlet with one that is grounding-capable, without installing a grounding wire. Or the grounding wire could be detached. On an old steel pipe conduit system, the conduit serves as the grounding, and there is no grounding wire.
Testing A Two-Slot (Probably Ungrounded) Outlet
Of course you can't use a three-prong tester in a two-slot outlet. You'll need to use a neon tester, multi-meter or pen-type voltmeter. To test for power, use the same procedure as for the three-slot outlet.
Although the two-slot outlet doesn't have a grounding slot, it's still possible that it's grounded. Here's how you test for it. Put one probe in the short (hot) slot, and touch the other probe to the screw in the middle of the cover plate. Make sure there's no paint on the screw, and that the screw isn't plastic. If the tester glows, the outlet is grounded.
If the tester doesn't glow, put one probe in the long (neutral) slot, the other on the cover screw. If the tester glows, the outlet is grounded, but the polarity is reversed. If the tester doesn't glow in either position, the outlet isn't grounded.
If the outlet tests as grounded, then you can safely use a grounding adapter on it so that you can plug in three-prong appliances. But you have grounding to the device only if you permanently attach the adapter to the outlet. Otherwise, even though the grounding prong is inserted into the adapter, it's not connected to the grounding in the outlet.
To attach the adapter to the outlet, turn off power from the outlet at the service panel by turning the circuit breaker off or removing the fuse. Test the outlet for power (above) to make sure there's no electricity. Remove or loosen the cover plate screw, plug in the adapter in the outlet, put the screw through the ring on the adapter, and replace the screw into the cover plate. Turn the power back on.
Testing A Switch
You can test a switch with either a continuity tester or a multi-meter set on continuity or ohms.
You must first turn off power at the service panel or fuse box. That's because either of the testers uses its own battery to send a small amount of electricity through the switch. It's harmful to the tester to have any other electricity there. Getting electricity back confirms that there is a path through the switch. That means that the switch is good.
The continuity tester is the easiest to use. Turn off power at the service panel. Then with a screwdriver, remove the switch cover plate. Test the tester itself by touching its tip to its clip. The tester lights. Now put the switch in the “on” position. Attach the clip to one of the screw terminals on the right side of the switch. Touch the tester tip to the other screw on that same side. If the switch is good, the tester lights.
You can do the same process with a multi-meter. Again, make sure you've removed power from the switch circuit. Set the meter for “continuity” if the meter has that setting. Otherwise, set it for ohms (Ω). When you touch the two meter probes together, the meter will make a beep sound. Now, make sure the switch you're checking is in the “on” position. Touch a probe to each of the two switch terminals on the right side of the switch. The meter beeps if the switch is good.
If the switch doesn't test good, it needs to be replaced. Either call an electrician, or consult a home wiring book for how to replace it.
Basic electrical troubleshooting is easy and safe if you pay attention to what you're doing and follow the rules:
Troubleshoot only when you are fresh and alert. Like with using power tools, that means no intoxicants lately.
Figure out ahead of time what you're going to do and how you're going to do it.
Don't touch any metal for any reason, even if you think there's no electricity there. This includes all wires, screws and water pipes.
Don't have water anywhere near your work.
Like with scuba diving, have someone nearby who can get you help on the very outside chance you get yourself in trouble.
If you're not sure of what you're doing, call an electrician.