Most users want (and should) protect their valuable equipment. Surge suppressors, which are also known by other names such as surge protectors, noise suppressors, transient filters, line filters and TVSS (Transient Voltage Surge Suppressor), protect your equipment by removing noise and spikes coming from the power grid – and sometimes also from the telephone line and from the satellite or cable TV line, if you have a suppressor with this option. But how do they work? What components do they have inside? How can you differentiate a good product from a bad product? Read on.

Besides the noise and spike removal, surge suppressors have other three basic goals. First, and the most obvious, to expand the number of AC outlets you have available near your computer or audio/video equipment – yes, surge suppressors can be used with any kind of equipment, and audio and video are the most common ones besides computers, as any noise coming from the power grid can appear as an audio noise or a video noise.

Second, to make sure that all your equipment is properly grounded. For grounding to work, you can’t cut the ground pin from the power cord of your equipments (including the surge suppressor itself) and you also must have proper grounding on your AC outlet – i.e., having an AC outlet with three pins and making sure that the third pin (the grounding pin) is correctly grounded. If you don’t have correct grounding the filtering circuit will not work correctly, as it basically re-route all voltage excess to ground.

Third, overload and short-circuit protection. All surge suppressors feature a circuit breaker that will shut power down if the total current pulled by your equipment is beyond its rated current. 15 A is the most common value. On several units the circuit breaker is built together with the on/off switch, so if you need to reset the breaker you will have to move the power switch to the off position and then to the on position again. On some other units the circuit breaker isn’t built together with the on/off switch and you will find a separated reset switch. Of course you need to check first why the circuit breaker activated, otherwise it will activate again as soon as you reset it.

Before disassembling some units to show you how their internals, let’s talk a little bit more on the aesthetics side of surge suppressors.

The most common problem nowadays is that we have several devices that may have a transformer attached to their AC plug – broadband modems, routers, printers and external hard drives are some typical examples. Also don’t forget about devices that you want to have on your desktop like battery chargers for you digital camera, cell phone or generic rechargeable batteries and may have to connect them to your surge suppressor because you may not have enough AC outlets near your desk.

The problem with these transformers is that they so big that they typically obstructs the outlet right next to it (and sometimes more than one, see Figure 2). So you may want to choose a surge suppressor that has “special” outlets for transformers.

Surge SuppressorFigure 1: Transformers like this one block the AC outlet right next to it.

Surge SuppressorFigure 2: Example of this transformer taking three AC outlets.

The suppressor portrayed in Figure 2 actually has one “special” transformer outlet, as you can see in Figure 3 (the one on the far right). The circuit breaker of this surge suppressor is together with its on/off switch, so you won’t find a reset switch on this model.

Surge SuppressorFigure 3: Surge suppressor with one transformer outlet.

In Figure 4, you can see a fancier surge suppressor with four transformer outlets. Of course you can still use these outlets with regular power plugs. The circuit breaker of this surge suppressor is separated from its on/off switch, so it has a reset switch (on its lower left corner in Figure 4). It also has a LED that indicates if grounding or the component used for peak protection (MOV) isn’t good, another LED that indicates that the circuit breaker is active (overload situation) and also cable/satellite filter and phone line filter. We will talk more about this feature later.

Surge SuppressorFigure 4: Fancier surge suppressor with four transformer outlets.

Some manufacturers solved this transformer problem by putting the AC outlets on cables instead of putting them on the surge suppressor housing, as you can see in Figure 5.

Surge SuppressorFigure 5: You won’t have problems attaching as many transformers as you want with this surge suppressor.

Now that we’ve talked a little bit about layout, let’s talk about what is most important: filtering.


Gabriel Torres is a Brazilian best-selling ICT expert, with 24 books published. He started his online career in 1996, when he launched Clube do Hardware, which is one of the oldest and largest websites about technology in Brazil. He created Hardware Secrets in 1999 to expand his knowledge outside his home country.