04.How surge protectors work
A surge protector can look a lot like a typical power board, but when too much voltage gets shunted down the mains line into the device it lets only a ‘safe’ amount through to the connected equipment. The rest it channels into the electrical outlet’s ‘earth’ or ground wire.
Most commonly for domestic units the crucial component that does this is called a MOV, or Metal Oxide Varistor. This component is made from a material which is a bad conductor of electricity until it receives a higher than normal voltage, then it becomes conductive.
When a spike or surge occurs at a certain level above normal voltage, the MOV becomes conductive and starts to carry the excess electric current back down through the ground wire, so the damaging high voltage doesn’t reach connected equipment. Once the surge ends, the MOV resumes its ‘dormant’ stage of being non-conductive. It’s a bit like an electrical version of a pressure valve.
Australian domestic wiring is designed for a standard voltage of 230–240 volts. If the voltage goes too far above that, it can damage electronic equipment, which usually has many sensitive components. If excess voltage lasts for a very brief time (1–2 nanoseconds) it’s called a spike. If it lasts longer it’s called a surge. Even though a spike or surge can be so brief their duration is measured in nanoseconds, they can still cause damage to sensitive components. All spikes and surges come under the heading of electrical transients.
Levels of protection
Possibly the most noticeable cause of a large surge can be lightning striking nearby, even up to more than a kilometre away. This massive electrical discharge quickly finds its way into the electrical grid and flows along power lines both above and below ground and anything else that is conductive.
A surge can also be caused by other less dramatic and far more common occurrences, such as switching operations in the power supply network, downed power lines, turning on or off large industrial equipment and faults with the electrical supplier’s equipment.
A direct hit by lightning, however, could instantly deliver hundreds of millions of volts that will be far beyond the capacity of any surge protected power board. Saying a surge protector will save your equipment from a lightning strike could be overstating the issue. A nearby strike within a kilometre or two however can send a massive surge in the order of several thousand volts down the line to your home, and here a good surge protector can be up to the task.
Some surge protection devices will specifically say they won’t protect against a lightning strike, while others will claim protection from lightning, as well as spikes and surges. Some will claim protection from spikes and surges but not mention lightning. Check the wording of the included documentation carefully as this could affect your chances of repair or replacement of the device or equipment if damaged.
In a lightning storm, it’s still good practice to unplug equipment completely from electrical outlets. Even turning off the switch might not save you, as the normal household switch only disconnects the active wire, the neutral and earth remain connected. So, if in doubt, pull it out.
Surge protection can also be built into your mains power board by an electrician, in the form or a surge diverter or surge arrestor. These were outside the scope of this test, but can provide a valuable first line of defence against surges.
False sense of security
Some surge protectors can give you a false sense of security. One of the problems with this type of device is that the surge protection component can fail, but the board can continue to work as a normal power board. This means that unless you replace it, the next time a big surge comes down the line it’s going straight to your now unprotected equipment!
Of the 12 boards we tested, only eight had a protection status light: APC P5B-AZ, Belkin F9S620au2M, CABAC PB10SP, Crest PRPBS6TC, HPM D105PA6, Monster AV800, PowerTech Plus MS4024 and Thor A12F.
In most cases, the onus is on users to check the status light frequently to ensure the surge protection components are still working. Out of sight, out of mind could also mean out of luck when that next big surge hits.
Unlike UPS units, for example, there’s usually no audible alarm to indicate a problem. Of the 12 boards we tested only one, the Monster AV800, had a built-in audible alarm. If your board lacks a protection status light, it’s a good idea to replace it every few years to ensure you are covered.
Test to destruction
Intrigued by the durability of some of the surge boards we tested, which passed the extreme surge 4kV test with flying colours, we wanted to see how durable they really are. So, we inflicted a series of even greater surges, of 6kV at 30 second intervals, to see how they’d perform. This test revealed that several models are surprisingly robust. However, as with the 4kV test, we didn’t factor the results into our final ranking.
Very unlikely though it may be, surges of this magnitude can occur in remote areas, where long cable runs and fewer cables can mean greater voltages transmitted from a lightning strike.
The boards that performed well in this test can be seen in the table below.
However, one result this test demonstrated is that with some boards the anti-surge circuitry can be burnt out, yet the board will still conduct power to connected devices.