Home Electrical Troubleshooting Background

House Wiring 101

When faced with troubleshooting electrical problems in a house, you can avoid watts of frustration by learning or reviewing things about your household electrical system. Here you will find a wiring diagram of a 4-way switch, learn how Code affected where a GFI outlet is hiding, and start to distinguish the different symptoms of a short, an open, a ground-fault, and an overloaded circuit. When you have learned enough, you'll be ready to go on to the Troubleshooting page for troubleshooting electrical problems in your own house -- do-it-yourselfer style. Enjoy House Wiring 101!  Disclaimer.

Did You Know?

1. A circuit breaker can appear to be ON but really be tripped.
2. The voltage at half of all U.S. homes is greater than most light bulbs are designed to run on.
3. A normal receptacle is sometimes ground-fault protected from elsewhere.
4. Home electricity doesn’t flow in one constant direction.
5. A turned-on dimmer switch normally produces some heat.
6. Most of a circuit can go out even when the breaker is on and is fine.
7. A GFCI receptacle will not trip for an overload.
8. Hair dryers sold today can use the entire capacity of a 15-amp circuit.
9. Replacing a switch or receptacle can open a can of worms.
10. Even if you knew all these, you can learn more by reading this page.

Your Home Electrical System

Electricity flows to your lights and appliances from the power company through your panel, its breakers, out on your circuits and back. There are many connections along these paths that can be disrupted or fail, and there are many ways that electricity could go places you don’t want it to. Here is a schematic picture of all the major parts of your home electrical system:

The Power Company.  Your electrical utility company and its distribution system bring power over wires and through switches and transformers from the generating plant all the way to a point of connection at your home. The utility’s system itself can have trouble that can affect things in your home. Its built-in safety features can stop power in time, but other connections, broken lines, storms, imperfections, or mistakes can sometimes allow unusual voltages into your system, possibly damaging parts of it. The sensitivity of home electronic equipment to this has made us more aware of this possibility, so that our use of surge protectors has become common. But some surges are difficult to protect against and can be similar to lightning strikes in their effects. This diagram gives a closer look at the source of 120 and 240 volts in the company's transformer:

Your Main Panel. Your central breaker panel (or fusebox) directs electricity through your home as a number of separate circuits, each flowing "out" from its own circuit breaker (or fuse) on one wire and returning from whatever is using the electricity to another connection in the panel by means of another wire. The breaker or fuse will interrupt the current (the flow) if it ever starts to approach a dangerous level. There may be in the panel a distinct "main" breaker that can shut off power to most or all the circuits. If not, there could be one near the power company's meter. These devices automatically turn power off, but connections at any one of these points -- at the meter, at the main breaker, inside the main breaker -- can fail or become unreliable, disrupting some or all the power in your home. Compare a main panel as I have diagrammed it so far with how a typical panel is arranged:

Circuits. A circuit is a path over which electric current can flow from and to an electric source. This concept could use some clarification. If it were always as simple as current from the source following only one possible path out to one light and back by one return path, then the operation or malfunction of a circuit would be easy to grasp. But it is not so simple. Code and convention define a circuit in a home as having its source at one of the home’s circuit breakers or fuses. Taking this as the starting place of the electrical source, then, we will find that most circuits in a home are complex, involving sub-branches like those of a tree. This next diagram lets you trace the path of one circuit as it goes through your system:

By Code, a dedicated circuit is used for each of most large appliances like the electric range, electric water heater, air conditioner, or electric dryer; these as well as electric heaters will have two (joined) breakers in order to use 240 volts rather than the 120 volts used by most other items. A dedicated circuit of 120 volts is usually provided for each dishwasher, disposal, gas or oil furnace, and clothes washer. Most other 120-volt circuits tend to serve a number (from 2 to 20) of lights and plug-in outlets. There are usually two circuits for the outlets in the kitchen/dining area, and these use a heavier wire capable of 20 amps of flow.

Circuits serving more than one outlet or light pass power on to successive locations by means of connections in the device itself or in the box the device is mounted in. So on any one circuit there are many places where electricity can fail to get through -- from the circuit breaker and its connections, through a number of connections at devices and boxes, through switches, and at the contacts of a receptacle where you plug something in. Troubleshooting electrical problems in your house will depend on a basic grasp of these matters. (Want help on How to label your panel‘s circuits?)

Wires: hot, neutral, ground. To understand the function that different wires on a circuit play, consider first our use of terms. Because a house is provided with alternating current, the terms positive and negative do not apply as they do to direct current in batteries and cars. Instead, the power company is providing electricity that will flow both directions 60 times per second between its transformer's terminals by way of wherever your home's wires give it a continuous path. Two of their terminals are isolated from the earth and the third is connected to the earth (grounded). We call these isolated wires hot or live because anything even slightly connected to the earth (like us!), when touching the hot wire, provides, along with the earth, an accidental path for that wire's electricity to flow between it and the transformer's grounded terminal. (See this very good Portrayal of shocks by an engineer-type). A hot wire is, we might say, one half of the path the circuit takes between two sides of the electrical source. The other half of the path is the neutral wire (in the case of a 120-volt circuit; for a 240-volt circuit it is an alternate hot). Whatever is using the electrical power (the "load") is situated between these two halves; when it is connected or turned on, current flows through it and both wire "halves".

Hot wires are distributed into your home through a number of circuit breakers or fuses in your panel. They are typically black, occasionally red or even white, and never green or bare. The earth-connected neutral wires in your home are also distributed from your panel, but from a (single) "neutral" or "ground" bar; these are always supposed to be white. Contact with them should not shock you because they are connected to the ground much better than you can be. Contact with a hot, even one that is white-colored, will tend to shock you. Even when they are switched off, we call these wires hot to remind ourselves that they will be and to distinguish them from neutrals and grounds.

Besides black, red, and white wires, the cables in homes wired since the 1960's also contain a bare (or green) ground(ing) wire. Like the neutral, it is ultimately connected to the power company's grounded terminal, but this ground wire is not connected so as to be part of the normal path of flow around the circuit. Instead, it is there to connect to the metal parts of lights and appliances, so that a path is provided "to ground" if a hot wire should contact such parts; otherwise you or I could be the best available path. In other words, when a ground wire does carry current, it is taking care of an otherwise dangerous situation; in fact, it usually carries so much flow suddenly, that it causes the breaker of the circuit to trip, thereby also alerting us that a problem needs attention. See if you can picture the different paths taken by normal current and a short-to-ground:

Switching. By code, convention, and good reasons, only hot wires are supposed to be switched, never neutrals or grounds. A switch is a device that continues the hotness of a hot wire on through to, say, a light or else discontinues that hotness. So the black wire between a switch and its light is not always actually hot; when it is not hot, its (black or red) color is still valid, to remind us that it will sometimes be hot. See how a household switch works:

There is a form of switching in which two or more switches can each control a light. These are commonly called three-way switches. They normally work by one switch continuing hotness to another on one or the other of two "traveler" wires that run between the switches; the final switch connects either the hot traveler or the unhot traveler on to the light, thus energizing the light or not. I give More discussion and diagrams of 3-way switches.

Other specialized switches include dimmers, motion sensors, photocells, timed switches, low-voltage switches, and "smart home" (X-10) switches. You can get my tips about these and other devices and appliances at Other electrical devices.

Tour of a Circuit. This is where you will see a house wiring diagram, though not of a whole house. There are diagrams (here's a Preview) of a switched outlet, three-way switches, a series of outlets, and all the switches and lights related to them. So that you can experience the ins and outs of a circuit in practice, take the Tour [or frames version]. (Those who like puzzles will even find three troubleshooting challenges at the end of the tour). Then to compare this same circuit as it connects in electrical boxes with how its cables would be run in a particular set of rooms in a home, go to Circuit Cabling. I recommend you view these files; you may recognize things in them that are like what you find in your own home.

For the more advanced. I am working on this Big Connections Diagram, which is to show all the possible ways wires connect in outlet, light, and switch boxes.

Want someone else's version of some of this background material? I am impressed with This FAQs page.

How Things Go Wrong

Why should a system which has few moving parts be subject to failures of various kinds? Realize that every technology designs its systems with economy in mind. Even the best available wire connector, for instance, could have been made from even better materials that would have made problems with it even less likely.

Also, there is such a thing as wear and tear on electrical components. Current flowing through wires and connections creates heat and other stresses that affect the quality of insulating materials and the conductivity of metal surfaces. Add to this the effect of repeated use -- where plugging and unplugging appliances at a receptacle gradually loosens its hold on the prongs being plugged into it -- and you begin to see what can happen.

Besides these there is the matter of workmanship. The reliability of the system depends on the care taken to set it up, from the engineers designing a switch to the person installing it. How tight should a screw be that holds a wire in place? This is something ultimately learned by experience, even though a manufacturer may specify what torque should be applied.

And finally, any time your system is reworked even slightly, there is room for error -- from ignorance or unintentionally.

So both the human and the material worlds contribute to the malfunctions this website is trying to pick up after. The need for home electrical troubleshooting is built in.

What are the kinds of things that could possibly go wrong in your electrical system? Let’s consider two ends of the spectrum. At one end, you are familiar with a light bulb burning out. On the other end, you have experienced times when neighborhood power to your home has been interrupted -- briefly or for a number hours. Between these, there are quite a variety of other ways.

To grasp the scope of possible problems, and to lay a groundwork for a strategy to solve them, consider the relation between symptoms and causes. We can categorize what goes wrong by the symptoms produced or by the cause, and these two aspects are related to some degree, as will be illustrated soon in a chart. First, consider the possible symptoms:

Symptoms Spelled Out:

1. Does not work. Some things don’t work. This is the most common trouble.
2. Goes on and off at will or blinks or flickers. Things are working now but in the past some things have gone out for awhile and later come back on their own.
3. Runs dim or bright sometimes. Lately, things often dim down or brighten at will or in response to turning something on or off. This goes on for more than three seconds at a time. This category is to be distinguished from the previous one.
4. Won’t go off. Something won’t turn off by means of its switch or other control device.
5. Shocks. Someone experienced a shock.

Now see the relation of these symptoms to their possible causes:

Causes Spelled Out:

1. Overload/Short/Ground-fault. I group these three causes together because they are ultimate causes whose immediate causes are tripped breakers, blown fuses, or tripped GFIs. Let me distinguish the three. An overload occurs when in its normal operation a circuit has carried a little too much current a little too long, so that the wires will be getting too hot, and so the breaker trips off to prevent this. You were running a little too much on that circuit. A short is an unintended connection from a hot wire to ground by way of the neutral wire or (less technically) by way of the ground wire or anything providing a path to the earth. A short will usually trip a breaker because the flow of current is potentially huge, not being limited and safe by design, as it is when running lights and appliances. Current still flows around from the ungrounded starting point to the grounded end point, and so it is still technically going in a "circuit". A particular short (in the broad sense) is the ground-fault. It involves Contact from a hot wire to something grounded other than the neutral itself; if there is a ground-fault interrupter device (GFI) ahead of it on the circuit, it will sense this and trip off. Even when a ground-fault is not strong enough to trip a normal breaker it is a hazardous "leaking" of current off of the intended path.
2. Circuit or main wire connection open. An open refers to an unintended discontinuity somewhere along a circuit’s path. It may be a break, a gap, or a deterioration. Typically, a wire has become too loose at a point where it is supposed to pass current on to another wire. Here are places that can develop an open:
   Here is a closer look at what is behind some bad connections:
   See a photo of What bad connections occasionally can look like. An open at a main wire -- at the panel, meter, or line from the power company -- will disable more than one branch circuit. In addition, it will affect several circuits in unusual ways. The combined 120 and 240 volt system provided to U.S. and Canadian homes is behind This weird dimming or brightening effect. (Here is a Site that explains the systems in other countries). A similar effect can appear in the case of an Open neutral of a two-circuit cable.
3. Ground-fault with no ground. Shocks become possible when a person’s body provides the unintended path for a hot (faulting) device, fixture, or appliance toward a grounded wire, device, fixture, appliance, pipe, or to the earth itself. Whatever should have grounded the hot item is either missing or out of contact with it (is open); otherwise it would have tripped a breaker or GFI.
4. Miswiring. Poor workmanship can result in the other cause-categories, but this one refers to actual mistakes made in connections, often when a device is replaced. See Replacing devices and Correcting connections.
5. Mis-set or bad device. Switches, outlets, light fixtures, and light bulbs can fail to operate as they should because of breakage, arcing, heat, internal wear, damage, corrosion, or manual settings on them that have been changed. This cause will tend to affect only the thing itself or, in the case of various switching devices, the things meant to be controlled by it.

Perhaps now you are ready to attack your household electrical problem using my step-by-step Troubleshooting Strategy Page. If you can't afford an electrician and are a little bit handy, I think you will find my electrical advice clear and helpful.

Testers

This Chart of Testers describes some of the most common, available, and simple testers that are useful for learning more about the status of things in your home electrical system. View some of these at this Tester retailer. Use them according to the manufacturer’s instructions, common sense, and Safety. Which testers are best for making certain tests is dealt with in The logic in choosing electrical testers and How to test for what. Ideas for some homemade troubleshooting testers are found at Tips for electricians.

Searchers who need to read the material on this page may be using terms found in this statement: Understand your wiring problem by tracing the overloading from the breaker box, along the electrical circuit, to the heavy appliances.