Checking for Incorrect Electrical Wiring

Safety First ... Turn off the Power

Before working on any electrical circuit or device, always turn off the power to the entire circuit by switching off the appropriate breaker in your home's service panel (breaker box).

After you've switched off the breaker, test any circuit wires or devices you'll be inspecting with a non-contact voltage tester. This inexpensive tool is about the size and shape of a permanent marker and allows you to test for power without touching any wires. Simply touch the tip of the tester to the wire in question (or insert the tip into an outlet slot or touch it to any device terminal). The tester can detect voltage through the wiring insulation, so you don't have to find the bare end of the wire, as you do with some other testers. If there's voltage, the tester lights up. No light, no voltage. 

Reversed Connections

Most electrical outlets (properly called receptacles) today are grounded three-prong outlets. They have one long straight slot, one short straight slot, and a roundish ground slot to accept the three prongs of a grounded plug. You will also see outlets with a slot in the shape of a sideways T, a short slot, and a roundish slot, indicating you have a 20-amp outlet. These 20-amp outlets are often seen in commercial or condo applications.

Older, ungrounded, outlets have only two straight slots, one long and one short. That's why you often have to flip over a plug to fit it into an outlet; it goes in only one way. This long/short design is called polarized and is a safety feature that predates the standard grounded outlet. 

Polarized outlets and plugs ensure that electricity flows in one direction only. This makes things like lamps and many appliances more safe to operate. But here's the catch: If you connect the circuit wires to the wrong terminals on an outlet, the outlet will still work, but the polarity will be backward. When this happens, a lamp, for example, will have its bulb socket sleeve energized rather than the little tab inside the socket. Guess which you're more likely to touch? You want the tab energized, not the sleeve. 

Inside an outlet's electrical box, the black (hot) wire should be connected to the brass-colored terminal on the outlet. The white (neutral) wire should be connected to the silver-colored terminal. If these connections are backward, the polarity is wrong.

Proper Grounding

In a modern home, almost every part of the electrical system is grounded, meaning it has an unbroken (if usually not direct) connection to the earth outside the house. When something goes wrong, such as a short or fault, electricity flows safely to the earth via the grounding system. 

Homes built in the 1950s and earlier may have few or no true ground connections. Is this dangerous? It can be, sometimes, very dangerous. But the fact is, most of these homes operate just fine without grounded circuits. That said, if you're adding new circuits or updating any part of an electrical system, you should always include a ground. It's not just smart; it's the law. 

If you have outlets on ungrounded circuits you can replace them with GFCIs, or ground-fault circuit-interrupters. These are special outlets that shut off the power if they detect a dangerous ground fault, helping to protect you against shock. They do NOT provide a ground, but they do make using the outlet a lot safer. 

One simple way to test outlets for grounding is to plug in a receptacle tester. If the tester indicates an "open ground," the outlet may have no means of grounding or there may be a ground wire, but it's improperly connected. It also could be grounded to a metal electrical box, but the box is not properly grounded. 

Too Many Wires Under Terminals

Installing more than one wire under any standard screw terminal is not only a risky move, but also it's a lazy one. It is nearly impossible to properly tighten two wires under a single terminal. This usually results in a loose connection. And loose wires are a very bad thing. If you find more than one wire connected to an outlet or switch terminal screw, correct the problem by joining the wires with a wire connector and include a pigtail, a short length of the same type of wire. Connect the pigtail—and only the pigtail—to the screw terminal in question. 

Proper Amount of Wire Insulation

Although it may not seem important, proper insulation length is very important on wire connection points. Stripping a wire to the proper length makes for a great connection. Stripping too much insulation exposes the bare wire too much and can become a point where someone can touch the wire or the bare wire may come in contact with the box or another wire, like the ground wire. in this case, some folks just cover the exposed wires with electrical tape, but the proper method is to re-strip the wire end to proper length.

Too little wire shouldn't be a problem then, right? Wrong! Too little stripped insulation means that some or all of the terminal is in contact with the insulation and not the bare wire. This either means that there is a limited connection, with resistance due to the insulation, or no connection at all. 

When stripping wire for a screw terminal, remove about 3/4 inch of insulation from the wire end. Shape the bare wire end into a hook and attach it to the terminal, so the open end of the hook is on the right. This means the hook tightens around the screw as the screw is turned. When the connection is complete, the wire insulation should almost touch the screw, but none of it should be under the screw.