Understanding the Function of Surge Protectors

When setting up a computer system, a surge protector is an essential piece of equipment. It fulfills a clear role: allowing multiple components to connect to a single power outlet. Given the many parts that comprise a computer system, surge protectors are highly beneficial devices.

However, the key purpose of a surge protector power strip — safeguarding your computer's electronics from harmful power surges — is undeniably more crucial. But how do surge protectors function, and when are they necessary? And how can you tell if the one you own is of high quality?

The primary function of a surge protector is to shield electronic devices from electrical "surges." If you're curious about what a surge protector does, the first question to ask is, "What exactly are surges?" Then, consider, "Why is it important for electronics to be protected from them?"

A power surge, or transient voltage, refers to a significant rise in voltage beyond the normal level in an electrical flow. In standard household and office wiring in the U.S., the typical voltage is 120 volts. When the voltage exceeds 120 volts, an issue arises, and a surge protector plays a key role in preventing such surges from damaging your electronics.

To grasp the issue, it's important to first understand what voltage is. Voltage represents a difference in electric potential energy. Electric current flows from one point to another due to a higher electric potential energy at one end of the wire compared to the other. It's a concept similar to water under pressure flowing from a hose — higher pressure at one end pushes the water toward an area of lower pressure. You can think of voltage as a form of electrical pressure.

A variety of factors can lead to a sudden spike in voltage:

If a surge or spike reaches a high enough level, it can cause significant damage to a device. This is comparable to applying excessive water pressure to a hose — the hose will burst under the strain. Similarly, when too much electrical pressure flows through a wire, it can cause the wire to "burst." In reality, the wire heats up like the filament in a light bulb and burns out, but the principle is the same.

Even if the increased voltage doesn't immediately damage your electronics, it can create additional stress on the components, gradually wearing them down over time. In the following section, we'll explore the role of surge protectors in preventing this damage.

Surge Protection

A typical surge protector allows electrical current to flow from the outlet to the devices plugged into the power strip. If the voltage from the outlet surges or spikes — exceeding the safe level — the surge protector redirects the excess electricity into the outlet's grounding wire.

In the most widely used type of surge protector, a component known as a metal oxide varistor (MOV) redirects excess voltage. As shown in the diagram on the left, an MOV creates a connection between the power line and the grounding line.

An MOV consists of three parts: a central piece of metal oxide material, which is connected to both the power and grounding lines by two semiconductors.

These semiconductors have a variable resistance that changes with voltage. When the voltage is below a certain threshold, the electrons in the semiconductors flow in a way that produces a very high resistance. When the voltage surpasses this threshold, the electrons behave differently, resulting in a much lower resistance. Under normal voltage conditions, the MOV remains inactive. However, when the voltage becomes too high, the MOV can allow a significant amount of current to flow, eliminating the excess voltage.

Once the excess current is diverted into the MOV and directed to the ground, the voltage in the power line returns to a normal level, causing the MOV's resistance to spike again. In this manner, the MOV only diverts the surge current while allowing the normal current to continue supplying power to the devices connected to the surge protector. To put it simply, the MOV functions like a pressure-sensitive valve, opening only when there is too much pressure.

Gas Discharge Arresters

Another form of surge protection is the gas discharge arrester, or gas tube. These devices perform a similar function to an MOV by redirecting excess current from the power line to the ground. Gas discharge arresters are commonly used in settings like power substations, industrial plants, or within office buildings, and they can be installed within the gas tube of a power transformer or mounted on external walls.

At normal voltage levels, the gas inside a gas discharge arrester is a poor conductor. However, when voltage surges beyond this level, the electrical power ionizes the gas, turning it into a highly efficient conductor. It channels the current to the ground line until the voltage returns to normal levels, at which point the gas becomes a poor conductor again.

Both surge protection methods employ a parallel circuit design — redirecting the extra voltage to a separate circuit. A few surge protectors use a series circuit design, where the excess electricity is not sent to another line but instead slowed down as it travels through the power line. Essentially, these devices detect high voltage and temporarily store the electricity, releasing it gradually. Manufacturers of these devices claim that their method offers superior protection because it reacts faster and prevents the disruption of the building's electrical system by not sending excess electricity to the ground line.

Some surge protectors include a built-in fuse as a secondary safeguard. A fuse is a resistor that conducts current easily under normal conditions. However, if the current exceeds a certain threshold, the heat generated by the resistance causes the fuse to burn out, severing the circuit. If the MOV fails to prevent the surge, the fuse will burn out, saving the connected devices. This fuse can only function once, as it is destroyed in the process.

Some surge protectors come equipped with a line-conditioning feature that filters out "line noise," or minor fluctuations in electrical current. Basic surge protectors with line-conditioning employ a relatively simple mechanism. As the hot wire travels to the power strip outlet, it passes through a toroidal choke coil, a magnetic ring wrapped with wire — essentially an electromagnet. The varying current in the hot wire charges the electromagnet, which generates electromagnetic forces that smooth out the small increases and decreases in current. This "conditioned" current is steadier, making it less taxing on your electronics.

Power Surges

Power surges happen when an event increases the electrical charge at a specific point in the power lines. This rise in electrical potential energy can send more current to your wall outlet. Several factors can lead to such a surge.

The most recognizable source is likely lightning, but it’s actually one of the rarer causes. When lightning strikes near a power line — whether underground, within a building, or along poles — it can cause a dramatic spike in electrical pressure, reaching millions of volts. This results in a massive surge that will likely overwhelm nearly any surge protector. During a lightning storm, it’s best not to depend on your surge protector to safeguard your electronics. The most effective defense is simply to unplug them.

A more frequent cause of power surges comes from the operation of high-power electrical devices, such as elevators, air conditioners, and refrigerators. These devices require significant energy to activate components like compressors and motors. This energy demand creates brief but intense power fluctuations that can disturb the steady voltage flow in the system.

Though these surges aren't as intense as those from lightning, they can still be severe enough to damage components either immediately or over time, and they occur regularly in the electrical systems of most buildings.

Other causes of power surges include faulty wiring, issues with the utility provider’s equipment, and downed power lines. The electrical system that brings power from generators to homes and offices is incredibly intricate. With numerous potential failure points and various possible errors, it’s almost inevitable that power surges will happen in today’s distribution network.

When to Use a Surge Protector

In the previous section, we discussed how power surges are common and unavoidable in our modern electrical grid. This leads to a fascinating question: if power surges have always been present, why didn’t we need surge protectors in our homes 50 years ago?

The reason is that the components in today’s advanced electronics (like computers, game consoles, and high-definition TVs) are much smaller and more fragile than those in older devices, making them more susceptible to electrical fluctuations. Microprocessors, which are critical in computers and many household gadgets, are especially vulnerable to surges. They function correctly only when they receive a consistent current at the proper voltage.

Therefore, whether you should use a surge protector depends on the type of device you're connecting to the power supply.

One drawback of surge protectors is that the MOVs inside can burn out after a powerful surge. That's why it's important to choose a surge protector that includes an indicator light to show if it's still working properly.

Even if you plug all your devices into surge protectors, there are still other sources that can send damaging surges into your equipment. Any line that carries signals into your home could also carry a surge, whether from lightning or other factors. For instance, if you have a coaxial cable connected to expensive equipment, you might want to consider a cable surge protector. Surges on these lines can be just as damaging as those coming through power lines.

Surge Protection Levels

Not all surge protectors are the same. In fact, there's a vast range in both performance and cost of surge protection systems available on the market.

Most surge protector systems come with some kind of limitation. Choosing the right one for you involves balancing the system’s cost with the potential loss of data or electronics. Much like insurance, it’s about finding the level of coverage you feel comfortable with.

To safeguard your devices from surges, you’ll need individual surge protectors for each outlet. These power strips vary widely in quality and capacity (which we’ll explore in the next section). There are three main types of power strip surge protectors:

Be cautious with some inexpensive power strips labeled as "relocatable power taps." These devices are merely designed to split a single 120-volt outlet into multiple power sources but don’t offer any surge protection. They may appear similar to surge protectors, so check the packaging carefully to confirm the features before buying.

A standard UPS offers solid protection, but you should still use a surge protector alongside it. While a UPS can block most surges from reaching your computer, it may be seriously damaged in the process. Using a basic surge protector can help preserve the life of your UPS, too.

Once you’ve determined the level of surge protection you need, the next step is to start shopping for a suitable unit. In the following section, we’ll explore the key factors to consider when evaluating different models.

Underwriters Laboratories Ratings

Selecting the right surge protector can be tricky, as many subpar products flood the market. While research into a specific model is essential for making an informed choice, you can gauge a product's performance by looking for certain quality indicators.

Start by considering the price. Generally, if a surge protector costs less than $10, you’re likely looking at a model with basic, inexpensive MOVs that provide minimal protection, making them ineffective against larger surges or spikes.

However, a high price doesn’t always equate to quality. To determine what the unit can really do, check its Underwriters Laboratories (UL) ratings. UL is an independent, non-profit organization that evaluates electrical and electronic products for safety. If a surge protector lacks a UL listing, it's likely substandard and may not have any protective components. Even if it includes MOVs, they could be poor quality. Cheap MOVs can easily overheat and cause the surge protector to catch fire.

While many UL-listed products are still of lower quality, at least you’re assured that they provide basic surge protection and meet a minimum safety standard. Make sure the product is classified as a transient voltage surge suppressor, which means it complies with UL 1449, the required performance standard for surge suppressors. Many UL-listed power strips, however, lack any surge protection components and are only rated for their performance as extension cords.

No surge protector is completely foolproof, and even the most expensive models may have significant flaws. Experts in electronics have differing opinions on the best ways to handle power surges, with some manufacturers claiming certain technologies are inherently flawed.

Understanding Surge Protector Ratings

When looking at a listed surge protector, you’ll notice a few important ratings. Pay attention to the following:

High-quality surge protectors often offer a guarantee on their performance. When shopping for more expensive models, look for one that promises to replace your equipment if the protector fails to shield it from a power surge.