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Tests and Measurements for Electrical Fire Prevention

 

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This article reviews the fundamental causes of overheating, as well as, the tests and tools commonly used to uncover overheating problems.

 

Root causes of overheating in electrical systems

Combustion requires both heat and fuel. Designers of electrical equipment are careful to use fire-resistant materials, making the electrical system a poor provider of fuel. The fuel for the fire usually comes from some nearby material, with the electrical system providing the heat required for ignition.

Poor connections.

Vibration or thermal stress can cause connections in power distribution systems to loosen. Contamination can corrode connections. Both factors increase the resistance of the connection.

Insulation failure.

One of the reasons that electrical fires are less common is that the quality of insulation is better than in the past. But any insulation system will still degrade with age, heat and contamination. The most extreme form of insulation failure is a short circuit.

Lightning.

One of the functions of the ground system is to provide a low impedance path to earth, allowing a lightning strike to pass with as little damage as possible. Surge suppressors rely on a good ground path to operate effectively.

Harmonics.

Most of the current that flows in a US electrical system cycles at 60 Hz. Harmonic currents contain higher frequency components that generate heat throughout the system. Harmonic distortion is present in any electrical system that supplies electronic loads like motor drives, computers, control systems or production machines.

Overloading.

If a load draws too much current, the system components upstream of the load have to carry that current. The main protection against overload is the overcurrent protection device which should open.

Wiring mistakes.

The electrical system in commercial buildings is a dynamic entity. Over time, tenants change, production lines move, and new equipment gets installed. In a time crunch, mistakes are common and although a system may operate just fine for a while, latent problems can be created.

Tests and measurements for detecting heat and failing components

The trick with detecting electrical fire hazards is knowing what an abnormal reading looks like. The best solution is to gather baseline readings for especially important components and equipment. That gives you a point of comparison.

Visual inspection.

Electricity may be invisible, but the effects of heating on metal and insulators are not. Discoloration or charring is a sure sign that components are overheating.

Thermography.

Thermal imagers can read the infrared energy emitted by an object and create a visible image of the object's surface temperature. Hot, loose connectors show up dramatically on these thermal pictures, especially in comparison to cooler, tight connections.

Connection/switch resistance.

Another method for checking connectors is by electrically measuring the resistance of the connection. On an energized system, a resistive connection will cause...

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