Nick Markowitz's Fire & Electrical Safety Section

By Al Colombo

One of the most common problems with household appliances is the line cord. After many years of use, it's not uncommon for the insulation surrounding the inner conductors of a line cord to become worn and frayed. This can result in electrical shock when someone touches the exposed wire. This should be of special concern to parents of young children because they like to play with them.

Even more dangerous still are line cords that have been replaced by people with little or no electrical or appliance-repair background.

To understand the mechanics behind line-cord replacement, it's important to understand how basic alternating-currernt (AC) works. Line voltage, as it's often called, usually measures between 100 and 125 VAC (volts of alternating current). Such a measurement is taken with a test device called a voltmeter.

Because less than 1 volt can kill a person, it's important that anyone who endeavors to repair the line cord on an appliance have a healthy respect for electricity.

Voltage and Current

Without going into a lot of mathematical or technical detail on what voltage and current is, let's examine how these two characteristics relate to one another and how they work together in making home appliances operate.

Voltage, for example, works a lot like a filled container and an empty container, connected together by a 1/2- or 3/4-inch pipe. It's the physical difference of the two elevations that create the pressure that causes water in the top container to flow downward into the empty container.

When an excess of electrons form at one end of an electrical circuit with a deficiency at the other, for example, there is said to be a potential difference between the two point. This potential difference, or "voltage," (or pressure, as in the case of the containers) causes electrons to flow from the electron-excessive side of the circuit to the electron-deficient side through the wires that connect them. It's the flow of these electrons that technical lpeople refer to as "current" flow. It's this current flow that performs the work in an appliance where voltage is merely the electrical pressure that causes the current flow in the circuit.

Power-Line Nomenclature

In a modern, up-to-date home, the cable that connects each wall receptacle to the electrical buss is made up of three wires. Typical house wiring, also called Romex, comes covered with a plastic PVC covering. Within this plastic sheath is a black, white, and a bare wire. In some instances, metal conduit is used, in which case the wire colors encountered will be either red, black, white or green.

In technical terms, the electric buss is commonly comprised of a "hot," "neutral," and a "ground" wire. The "hot" conductor is the most dangerous and you should always be extremely careful not to touch it at any time, even when you think the power is off.

The "hot" wire is dangerous because it's electric potential is 110 volts above earth-ground, which is the same potential as your body when you're in contact with earth ground. Those unfortunate enough to contact the hot wire in the electrical power buss are often critically injured.

The "neutral" conductor in the electrical power buss is usually at or near earth-ground potential. Therefore, if you should come into contact with the neutral wire while you're touching earth-ground, nothing will usually happen. This is not the case, however, if you should touch the hot wire at the same time that you touch the neutral. The same holds true if you should come into contact with both the hot and earth-ground wires. In either case, you will experience the full 125 VAC potential of the single-phase power line buss.

To prevent this from happening to you, disconnect the line cord from the electrical power buss before you begin working on a household appliance. This usually consists of unplugging the line cord from a wall receptacle.

Replacing Line Cords

Before you rush out and buy a replacement line cord for your appliance, be sure the line cord that you buy is the right one for the job. Most line cords have to be flexible, so the appliance that it's attached to can be moved from place to place in the home. This requires the use of stranded wire, or wire made of individual metal strands. Line cords made with solid wire will work equally well in situations where the appliance is stationary.

Gauge Amps 12 40 14 35 16 24 18 18  Source:    NEC

Another factor that you must consider is that of wire size. The size of both stranded and solid wire is usually expressed as a numeric quantity, usually referred to as the gauge of the wire. Most line cords are made with 16 gauge conductors, which are capable of handling 24 Amps (A) of current (see chart). The values shown in the chart to the left are in free air at a temperature of 90 F

These ampacities decline as the ambient temperature increases. In reality, the safe amperage of any line cord made using any of the gauges shown in the chart is about half of that shown. This is because the chart shows maximum amperages whereas the safe limit of these conductors is a lot less. In addition, overcurrent protection for a 14 gauge conductor should be 15 A and 20 A for 12 gauge conductors, according to National Electric Code (NEC).

The insulation that protects a line cord is also important, not only to the integrity of the conductors within it, but also from the standpoint of electrical safety. A quality line cord is made up of two or three conductors, each bundled together with a layer of fiber and then a rubber coating to protect it. All two or three bundled conductors are then encased inside of a coating of rubber, called a "jacket."

Smaller appliances often use zipcord instead of the heavier appliance cord discussed so far. Zipcord is easy to recognize too, because it is made up of two conductors sealed with a thin plastic between them. This type of line cord is not as physically strong as the other because the the two conductors are coated with just the one plastic coating, unlike better line cord in which each conductor is wrapped with fiber, coated individually with rubber, and then all the conductors coated again by a rubber jacket.

Working with line cord

When cutting into either type of line cord, be careful not to nick or cut the individual wires that comprise each conductor. To do so can result in damage. Damage realized now, but not apparent at this time, can turn up later in the form of a broken conductor. The most common damage is usually due to making too deep a cut or nicking the wires of one of the conductors. A nick, combined with enough physical vibration, can result in broken wires later.

Here's how to cut the insulation away from the conductors in a jacketed line cord:

1. Carefully cut the jacket in a circular fashion approximately 1 in. away from the end of the cable by gently rotating the knife around the cable until an incision is made all the way around it.
2. Pull the rubber jacket off the cable with your hand.
3. Unwind the rubber coated conductors and the fiber lay that separate them.
4. Cut the fiber lay off with a pair of scissors or a knife. This will make the job of working with the rubber coated conductors easier.
5. Use a pair of wire strippers to remove the rubber insulation from each of the conductors or use a knife in the same manner as when the outer jacket was removed.

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