An AC electrical system is designed so that no arcing can occur, but changes can happen over time that make the system susceptible to arcing, and this can create a flash breakdown that is likely to cause a fire. The following are four problems that can create this type of arcing.
Problems with insulation
One of the most common reasons for an arc flash is aging insulation. Although the insulation may have been sufficient at the time of the installation, it has degraded, and how is has become brittle with breaks in certain spots. Sometimes this insulation may look good on the outside, but it has become thin in certain areas. It is in these areas where arcing can occur. Another problem is with poor insulation. This is most common when substandard repairs are made with poor quality material, especially insulation. The lifetime of cheap insulation can be short, and an arc flash breakdown can occur that leads to a fire, catching people off guard.
Voids or gaps
Gaps can form over time in places where none existed before. There are many reasons for this, and much of it is dependent upon the specific electrical system. Suffice to say, cables and components can shift because of the movement of the ground or vibration in the building. People can also be responsible for some of this movement. These gaps allow particles to charge in the air, and this can lead to a flash over that can cause a fire.
An accumulation of dust
Dirt and dust can build up over time. This dust can become a conductor at high voltages. This is often common near terminal points that are sufficiently spaced so that no arcing can occur, but with a build up of dust, the effect is to decrease the distance between the terminals, and you have an arcing problem.
Corrosion
This can happen anywhere in an electrical system. Corrosion is most common in areas of the country where there are high humidity levels. In buildings with electrical systems in basements, often a humid environment can lead to corrosion on the wires and terminals where the wires connect. Corrosion will usually be a danger to the insulation of the electrical system, and once again, this can lead to an arc flash breakdown.
The best way to avoid the dangers associated with arcing in your electrical system is to have an arc flash hazard analysis done. There are companies that specialize in this work and have the ability to perform electrical testing and do a visual inspection of your system.