Whole House Surge Protector: How It Works

You might understand the basic concept behind a whole house surge protector to stop power surges caused by external sources from entering your home through your power lines; but do you know exactly how it works? Power surges can come from a number of sources outside of your home, everything from your utility company having grid issues to lightning. (note: A direct lighting strike within a few hundred feet of your home is likely to do major damage regardless of the protective equipment installed.) When these surges are created they look for the most immediate path to escape. This would be your home’s power lines. What a whole house surge protector does is acts as a barrier that stops these transient surges from causing damage to electronics inside the home.

How does it do that? At normal current levels, the WHSP sits idle letting through normal voltage (called let-through voltage) that powers your home. If that level peaks to an abnormal high, it triggers a response (called the clamping voltage) from the protective device. Through MOV technology the surge protector absorbs the transient voltage and pushes it to a ground line while normal current flow continues into your home.

MOV is short for metal oxide varistor. Within the surge protector several MOVs are attached to the hot power line and connect to the ground line. A single MOV is made of metal oxide granules coated in a protective covering and connecting to both lines via semiconductors. The semiconductors are reactive to voltage fluctuations. If there is a sag in voltage level the MOV creates a resistance pushing current away from it, but when voltage levels increase, that resistance changes and the MOV becomes conducive to excess power. Basically, it provides an alternative route for the excess energy on the line, like a valve opening under pressure.

As this excess is diverted safely to the ground area, normal power flows continue on a normal path to your equipment so there is no interruption in power. Once the surge passes, the MOV resistance increases again to push all current to your equipment.

The downside to MOV technology is that the MOV degrades under each surge it intercepts so that eventually replacement of the house surge protector is necessary. The upside to this is that most modern devices have indicator lights on them that will alert you when it’s time to replace the model.

Whole house surge protectors are excellent tools against high current surges. They tend to have a higher capacity to absorb surges which can be significant against external sources. You shouldn’t depend on a whole house surge protector for total protection however. They have a higher clamping voltage, which is not so good for delicate equipment like computers; and they tend to having slow response times. And again, they respond only to external sources of power surges. There are internal surges within your home that can cause further damage.

The best defense is to have a layered system consisting of whole house surge protection and individual point-of-use devices for each electronic or electronic network in your home. Single surge protectors have faster response time and protect against internal surges caused, for the most part, by recurring powering up and down of large appliances, brown outs (power sags) and temporary blackouts, etc.

If you are interested in purchasing a whole house surge protector, here are some recommendations: