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How Does A Surge Protector Work?

I’ve Always Wanted To Know:

How does a surge protector work?



If you own a computer, a television or any other piece of expensive electronics you should know what the above picture is. A surge protector is a key part of protecting your gadgets from damage but how exactly does it work? When you buy one what should you look for and what do the various terms mean?

In the USA standard wall voltage is 120 volts (120v). A surge is a term for when the voltage exceeds the standard 120V for a duration longer then 2 nanoseconds. Common causes of surges are lightning strikes, cycling of high energy demand appliances/systems and power delivery system failures.

A surge protector at it’s most basic level has a circuit design which works normally at regular household voltages but once a surge happens will divert the extra power to the ground plug in the power outlet. The design of these circuits use either a MOV (metal oxide varistor) or a GDA (gas discharge arrestor) and both of these feature the ability to have a variable electrical conductivity.

Electricity will always take the path of least electrical resistance so the variable conductivity portion of the circuit (MOV or GDA) under normal 120v conditions makes a very poor conductor and hence the electricity flows normally. Under higher levels of voltage the variable conductivity portion changes and becomes a very good conductor of electricity allowing the excess current to be conducted through that path and into the ground. The design of the circuit is such that the excess current goes to the variable portion of the circuit and into the ground and the normal voltage is allowed to continue to your device.

As a last ditch fail safe some surge protectors will include a fuse (some have reusable circuit breakers or replaceable fuses), after the variable conductivity portion of the circuit, which allows current to pass through under normal voltage conditions and will burn out causing the circuit to break under high voltage.

So what does all the information on a surge protector package mean?

Number of Outlets: The number of outlet’s the surge protector has. Pay attention to location because if they are too close to each other or angled oddly some plugs may take up 2.

Extra Ports: Ports like USB can be useful to charge phones and portable electronics while ethernet and phone lines ports can protect devices connected via those plugs.

Joules Rating: The amount of energy the surge protector can absorb before it fails. Higher is better and I wouldn’t buy anything under 200 Joules.

Clamping Time/Response Time: The speed at which the protection engages. Faster is better and 2 NS or better is best.

Protection/Guarantee Value: This can be a tricky beast as the terms are very specific and what type of damage is covered. The guarantee may also only cover a pro-rated value can affect the true value of the guarantee.

Pass Through Voltage: The amount of energy that is let through when the surge suppressor is engaged in a surge. The lower the better as more pass through increases risk of damage to sensitive components.

AVR: Automatic Voltage Regulation is a feature which prevents brown outs and regulars voltage and is usually only available in uninterpretable power supplies not basic surge protectors.

Replaceable Fuse/Breaker: This let’s you know if the surge protector includes a replaceable fuse or breaker which can be replaced or reset if it’s tripped.

The general rule “you get what you pay for” applies with surge protectors with a sweet spot being in the $15 to $30 price range. Prices go up exponentially the better the surge protector so buying at the top of the line should be reserved for very expensive equipment which serves a critical purpose such as business servers or multiple computers.


P.S. Shameless plug here: WorldStart has a fantastic two port surge & USB charging protector which is great for charging two mobile devices and protecting your computer and monitor. Click here [1] to check it out.

Do you have a general technology or electronics question you always wanted to know like “How does a Microwave work?” or “Why do LED’s last so long?” Write me at Tim@WorldStart.com [2] and your question may be answered in an upcoming “I Always Wanted To Know.” For specific computer support questions ask our writers by clicking here [3].