Frequently Asked Questions:
Household Switches, Bulbs and Testing

The categories listed below are geared to solving malfunctions and miswirings in your electrical system, especially regarding light bulbs and switches. For code or design concerns see Basic wiring. For an overview of my troubleshooting information and tips, go to The Circuit Detective Home page. For FAQs on other topics go to Troubleshooting or Basic knowledge.

Page Menu Light bulbs

Why do the bulbs of a certain fixture burn out a lot?

When a fixture cannot dissipate the heat of its bulbs, it takes a toll on the bulbs and on the fixture's sockets and wires. If the lights are ones that are left on a lot -- like outdoor lights left on all night -- then the bulbs may be living their full life but will simply have to be changed more often than others. But other things can contribute to early failure. Bulbs may be of cheap quality. Or there may be loose arcing connections at the socket or in connections to the light.

Why do many bulbs around the house burn out sooner than they should?

There are various reasons that bulbs will burn out too soon. Bulbs may be of cheap quality. Or there may be loose arcing connections in the wiring of a circuit. The life expectancy of a bulb will also be affected by the quality of power from the power company. This includes the little surges and spikes that are better known for their effect on computers. But it also includes the basic voltage level coming to the home from the utility. Many homes receive more than the average 120 volts that most bulbs are designed to handle and this shortens their stated life. A good solution to this is to look for the same bulb but with a "130v" rating stamped on the bulb instead of "120v". The light output of these won't be quite as bright, but you will spend less of your time getting the ladder or stool out again. See my Light bulb article.

Several bulbs (got real bright and) burned out about the same time.

You may have a loose neutral that is shared by two circuits and that sometimes allows high voltage to hit one of the circuits. See Two circuit. Or a poor neutral could be the main neutral. See Main open. Or none of the above (often hard to know what was responsible, after the fact).

Switch questions

Why are switches called 3-way when there are only two switches?

Only because there are three terminals on the switch mechanism, which isn't a good reason in my opinion. It is true, however, that the switches used to switch lights from multiple locations are not all the same type of switch. Two of them have the three terminals, but any additional locations beyond the two have to use switches with four terminals, called 4-way. To be even more technical, a 3-way switch is a single-pole double-throw switch, and a 4-way switch is a double-pole double throw switch arranged for pole-reversing. See 3- and 4-way info.

We replaced some switches and now the new ones don't work quite right. Why?

You probably hooked the new ones up incorrectly. If the switches involved were 3- or 4- way type, the new switches may have a different arrangement of terminals than the old ones did. If the switches involved were normal on-off (single pole) type and there were more than two wires to attach, you may have attached a wrong wire somewhere or you may have failed to attach one at all, since the switch only seemed to call for two. See Pitfalls of upgrading.

I lost track of how the wires were connected to the old switch. How can I know what to do without trying dozens of possibilities?

For this you need to learn more about how switches work or more about how wires in an electrical box are able to use the switch terminals to achieve switching or to achieve a passing of unswitched hotness on to more of the circuit. See my Tour of a circuit or Correcting connections.

Can you help me hook up a 4-way switch right?

Yes, I can at least advise you so your choices and experimentation are minimized. Two of the switch's terminal screws are one color (brassy?) and the other two another color (dark?). Of all the wires in the switch box, two that come from one cable as it enters the box will attach to the two screws of one color, and two wires that come from the other cable (I hope there are just two cables total) will attach to the screws of the other color. If there are more than two wires in both of those cables, the third wires of each cable would attach to each other, not to the switch [hopefully these "third' wires were identified by already being joined, so that you don't have to experiment to find out which of the three wires in a cable is this "third" one]. Colors can vary. See 3- and 4-way info.

Electrical noises or sparks

Why is my light, switch, or breaker box humming?

Many dimmer switches will set up a hum at the light bulbs. At the breaker panel, the 60 cycles per second of your alternating current is able to set up a vibration or slight buzz or hum in some components there. Fluorescent lights, transformers, and an electric water heater can be heard humming also. All these are fairly normal, but if a hum is quite loud, it may mean a component is loose or close to failing. I have come across wet circuit breakers buzzing as they boil their water and a case where a loud hum was a breaker carrying a significant overload without tripping as it should have.

Why does my breaker hum or spark and then turn off?

If it makes this noise as soon as it is turned on and then trips off quickly or within ten seconds, there is a short circuit occurring somewhere out on the circuit. See Short. If sparking or "fizzling" is heard or seen but the breaker doesn't go off till a minute or more has elapsed, the breaker itself is probably having a connection problem and will probably need to be replaced, with the new one put in a different position in the panel if possible.

Smells or is hot to the touch

Should I be concerned that a certain switch or outlet gets hot?

An outlet getting hot means that wires connecting to it are loose and need help or that the outlet needs to be replaced because its receivers that a cord plugs into are weak. I would be concerned to take care of either of these scenarios. A hot switch is usually a dimmer switch (it may or may not still be able to dim lights). If the dimmer is trying to dim more than 600 watts worth of light bulbs, it is probably overloaded. In that case install one rated to handle more watts or replace bulbs with lower-watt ones.

Why is a circuit breaker so hot?

Breakers will be mildly warm when running things, but if one is hotter (not necessarily too hot to touch) it might be having trouble with a poor connection at or in it. Consider what it is running. If a heavy load (a space heater, for instance) has been running for perhaps a solid hour, this would be normal, even though the breaker might trip soon from the heat.

I've smelled something funny like hot plastic; what might be happening?

It isn't always easy to pinpoint where smells are coming from, but try. It might not be from an electrical source, but it might be. Sniff up close to outlets and switches when you notice the smell. Ask your dog to help you; seriously. If the smell is from something electrical, it will be from a poor connection that is creating heat, melting or charring plastic components. This presents a possible fire hazard.

Fire dangers

To be safe, should I have my whole electrical system checked out, and how often?

Without any definite specific symptoms, there is no reason to have things checked more than once, if that, during your tenure at a home. Unless you enjoy being paranoid. And don't let anyone confuse you between technical code violations and active hazards.

Outdoor wiring problem

How can I tell if a short, ground-fault, or open outdoors is in the earth or at a fixture/outlet?

If you can get access to all connection points of this line, you can unconnect just fixtures and outlets from the line and see if the fault remains when you try to reset. Otherwise, unconnecting where you can will let you narrow the possibilities down in a divide-and-conquer fashion. See Short and Ground-fault. An Open in the yard is a little likelier to be at a connection above ground, where it doesn't end up shorting so easily.


What is the right tester to use for my problem?

See Testing.

What does this 3-prong outlet tester mean by an open ground, open neutral, reverse polarity, or "hot and ground reversed"?

See Outlet corrections.

How would I test for a good or bad neutral, hot, or ground?

The best all-around is a neon tester. With one probe in the palm or your hand and the other to a possible hot, it glows for a hot. With one probe to the hot, it glows even brighter when the other is to a good neutral or ground. For other ideas, see Testing.

How would I test for a good or bad switch, receptacle, GFCI, breaker, or fuse?

(Also see Testing).
If a hooked up non-dimmer non-3way switch shows hot at one terminal (neon tester in hand) but not at the other when the switch is turned to ON, the switch is bad. Or just join the switch's two wires; if the light works but didn't for the switch, the switch is bad. A receptacle may need replacing but that will be from not holding plugs well, or from it having overheated from a poor wire connection, or from being simply broken. These things need looking for; there is no other way of testing for "badness". If a GFI that can run things won't trip off for the test button, replace it. And if a GFI with good hot and neutral at its line terminals won't reset and run things when no load wires are connected, replace it (I have seen this only once or twice). Other than these, the GFI itself is good. A breaker's screw showing hot for your neon tester is good 95% of the time. If moving a breaker's wire to another breaker changes nothing in the circuit's behavior, the breaker was fine. A screwed-in fuse lighting a one-probe-in-hand neon tester touched to its outer threads is good; if it doesn't light, the fuse is bad IF it lights on the fuseholder's center when the fuse is removed. A cartridge fuse that can be probed while in place is good if one end is hot and neon probes to both ends gives no light; if one or both ends are hot but probes to both ends gives light, it is bad. If fuses must be pulled out to test, an ohmmeter showing 0-5 ohms means good, otherwise bad.

At not-working outlets I find full voltage between hot and ground but not hot to neutral. Why?

The neutral is open somewhere (poorly connected). See Outlet corrections.

The white neutrals at some dead items of my circuit register some voltage to ground. Why?

Something among the not-working items of the circuit is turned on, allowing hotness from the good hot wire to go through the lightbulb filament, say, and show up as somewhat hot where you are testing the white wires (which are usually neutral [grounded] but not now). See Testing.

I get a reading on my voltmeter or ohmmeter that I don't understand. Am I testing the right things?

Maybe not. There are a lot more readings hard to explain than those that make sense and tell you what you need to know. I don't test anything but what I know will probably give me usable information. When I don't understand a reading, I don't let it distract me; I think of a different way to test out what I need to know. Of course, knowing what and where to test is important and is worth some thought. See Testing logic.

My non-contact volt "stick" says something is live or dead, but other testers disagree. What's up?

A non-contact voltage-presence indicator is rated to say when a certain level (or greater) of AC voltage is present. In practice I have found that that level is elastic. Lower voltages can set it off at times, especially when placing the stick very close to a wire. Also voltage induced onto a wire from nearby wires can register. So it is often helpful to confirm what a stick says using other testers and to give the others higher credibility. See my Chart of testers. Live underground cables that are still close to the earth may not register liveness for a stick.

Electrical questions about repair

Am I allowed to make a splice in the breaker panel?

Yes. It would have to be 75% full of wires for the answer to be No.

Why would a new breaker go bad after awhile, like the old one did?

Because the way the old one went bad was by bad contact with the busbar, so that arcing there damaged the busbar. Put another new breaker in, but in a better place.

What is the best way to connect wires at a receptacle?

By pigtailing, if you do a good job of it. Second choice: wires wrapped clockwise under side-screws. Third choice: use a receptacle whose side-screws clamp the wires tight in holes. Last choice (and only for 14 gauge wire): the "quick wire" push-in holes on the back of the receptacle; this actually does OK most of the time and is the most common.

©2005-2020 Laurence Dimock