People often think of only electronic gadgets, such as computers, game consoles, and audiovisual items, as being at risk from electrical surges. Actually, nearly every electric item in a house today has some sort of sensitive electronics that can be damaged by a surge. These include kitchen ranges, dishwashers, vacuum cleaners, air conditioners, and fans.
A common source of an electrical surge is lightning during a thunderstorm. The voltage and current spikes from just a single lightning strike are enormous, and there are typically many for the duration of the storm. If your house and wiring experience a direct or very nearby hit by lightning, even a good surge suppressor will probably not be able to protect all electronic items.
When a storm is forecast and you begin to hear the thunder off in the distance, unplug as many of your electronic devices as possible. This actually is a good idea anyway because many devices draw a lot of electricity even when you think they are turned off. Just switching them off may not be adequate protection from voltage and current surges. A huge voltage surge can arc across an open switch and still fry the electronic components in an expensive device.
Many times, it’s the repeated smaller electrical surges that damage the majority of electronic equipment. These can be generated by the switching on and off of inductive equipment (usually electric motors) in nearby businesses. Some of these smaller surges can even be generated by motors from your own vacuum cleaner, refrigerator compressor, or clothes washer through your home’s wiring.
It usually takes a long time for these numerous smaller surges to cause failures. One common result is that the wire and circuit board insulation slowly breaks down from each small surge and normal aging. Eventually, a wire may short out or the electronic component begins to malfunction, and the device fails. These surges can also reduce the life of many types of light bulbs.
There are several types of whole-house surge suppressors available designed to protect all of the wiring circuits in a house. Some mount on the circuit breaker panel indoors or are built into a circuit breaker. Others are designed to mount at the base of the electric meter. Many electric utility companies sell and install the units that work with electric meters for you. Check with your local electric cooperative to see if it offers this service. The circuit breaker panel models are not difficult to install, but I recommend hiring an electrician to do it for you.
There are differences in the protection provided by various surge suppressors. A common design uses metal oxide varistors (MOV) to dissipate the surge before it flows through the house wiring. You can conceptualize this as a floodgate. At normal voltages, the gate is closed, preventing leaks. But if the voltage gets too high, the gate opens, allowing the excess damaging current to pass to ground, protecting the equipment.
If the components (including MOVs) in a surge suppressor are too small, they can’t handle the surge, and they fail. Using larger components, rated to handle more Joules (a measure of energy), allows the suppressor to safely dissipate a larger surge. When comparing surge suppressors, a higher number is better for the total energy dissipation. Clamping voltage is the voltage that is required for the “floodgate” to open—for the MOV to conduct electricity. A lower number for this is usually better.
Even though the surge suppressor protected your electronics, a large surge may burn out the MOVs. Many models have a light on them to indicate if it is still functioning. Check it regularly and especially after a thunderstorm. On the one I use at my home, the light comes on only when the unit has been damaged by a surge and needs to be replaced.
It’s also important to note that many electronic devices like computers and entertainment systems have multiple connections, including satellite or cable, phone, or network, in addition to the power connection. Any of these can serve as a path for a surge to enter the device and cause damage. Surge suppression installed on the power line doesn’t guarantee protection.
For the most sensitive electronic devices, also use point-of-use surge suppressors for extra protection. They are not expensive and make it convenient to completely switch off the power to save electricity when the device is not being used. When purchasing one of these surge suppressors, look for models that are tested for compliance with Underwriters Laboratories (UL) Standard 1449, or ask your local electric cooperative for advice.
James Dulley is a nationally syndicated engineering consultant based in Cincinnati. If you have a question about energy use or energy-efficient products, send it to: James Dulley, Electric Consumer, 6906 Royalgreen Drive, Cincinnati, OH 45244; or visit www.dulley.com.