Lightning Strikes and Power Surges Continued

Lightning or Power Surge?

It is not easy to tell whether a piece of equipment was damaged by lightning or by what is commonly know as a "power surge". Getting to the bottom of this matter is important since property policies often exclude damages caused by artificially generated energy (hydro), while boiler policies often exclude damages caused by lightning. In many cases this will become grounds for dispute over coverage.

Let us look at a classic example. An insured claims that he saw the lights flicker on and off during a lightning storm. A few moments later it was discovered that the rooftop air conditioner had ceased to function, meanwhile everything else in the building seems to be working just fine. Service technicians were called. Upon examination it was determined that the windings in the compressor motor had burned. The suspicion was that the motor had been "hit by some kind of a surge". Was the damage caused by lightning?

What seems to be most puzzling is that the air conditioner was the only item that was damaged and the problem was localized to the relatively robust compressor motor. Nothing else in the building, including sensitive electronic equipment, was affected.

If you look a bit deeper you may find that this was what most likely happened: The compressor motor was running at a normal steady rate when the problem started. When the power flow was repeatedly interrupted by lightning, the motor was forced to shut down and then restart. This happens over and over.

Every time a motor starts it must draw in a substantial amount of electricity in order to build up speed and momentum. This is the reason for the loud humming noise and the dimming of lights each time a motor starts. This large inflow of current causes the internal motor windings to heat up. When the starting procedure repeats many times over during a short time period, the tremendous heat built-up will eventually cause the windings to burn and the motor to fail.

It is a true paradox to define whether such damage was caused by lightning or by energy from an artificial origin. One can argue that power interruption was a direct result of lightning. At the same time one can also argue that the energy which caused the motor to burn was plain, ordinary electricity, generated by the local utility company.

Another often seen type of lightning related damage inflicted on large, industrial type three phase motors is called "single phasing". Three phase motors, depending on the design, typically receive power from three separate lines, and sustain operation by using three groups of windings. If any one of the three supply lines loses power when the motor is running at a steady state, the partial loss of power will cause the remaining winding groups to draw excessive current and become instantly overloaded. If not shut down immediately, the overloading condition will cause the motor to become overheated and will burn out rapidly. Once again, lightning might have contributed to the partial power loss in one of the supply lines, but the energy that caused the motor to burn out was plain, ordinary electricity that was supplied by the local utility company and not lightning.

What is a Power Surge?

A genuine power surge is caused by abnormal events, such as the sudden opening or closing of main switches at a substation; wire crossovers, as a result of an accident or a vehicle striking a power pole and major equipment malfunctions. These surges are characterized by a sudden in-rush of voltage that is significantly higher than what is considered normal. The usual tell-tale signs are the sudden brightening of lights, television and computer screens, burned out light bulbs, blown fuses, etc.

Unfortunately, not every case is simple and "cut-and-dry". A study of the overall situation and the surrounding elements is required before any definite conclusions can be drawn.

It is a good idea to look for the following characteristics when attempting to determine whether the electronic equipment was damaged by lightning or by a power surge:

A lightning surge is typically very high in voltage, low in current and is very short in duration. A power surge is often the opposite. As a result, visible evidence left by lightning is usually very localized and more intense, due to the fact that the energy discharge is very intense but is of a very short duration.

Look for signs such as: a white, chalky appearance in solder joints; pitted or exploded micro chips; evidence of melted or vapourized small components or connections, etc. Evidence left by a power surge is often more widely spread and is of lower intensity, due to the fact that the energy discharge is less intense but is of a much longer duration. Look for physically burned wire bundles, groups of overheated components such as: resistors, exploded capacitors, etc. Unfortunately, not all lightning and power surges leave the above mentioned visible signs.

Look for points of entry. A power surge can only enter through wires and cables that are connected to "live" power sources. A lightning surge can enter via any long cable which is capable of inducing energy, regardless of whether it is connected to a power source or not. Cables such as power lines, telephone cables, TV cables and computer cables are the prime candidates for inducing surges during lightning strikes. It is always necessary to study the overall picture and establish the complete pattern before making a determination as to cause.

By Danny K. Fung
May, 18 2000