Review Surge Protectors: Learn What's Required to Prevent Damage

Updated on March 27, 2017
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Glenn Stok is skilled at researching and evaluating all kinds of products and has a knack for clearly explaining their features.


It's important to understand how power surge protectors work so you can make the right choice. Selecting the right one will properly protect your expensive electronic equipment.

Many people think they are saving money by buying a low-cost surge protector that gives little or no protection, but good protection doesn't have to be expensive either. Selecting the right one is just a matter of knowing how it works.

The purpose of a surge protector is to divert voltage spikes safely to ground rather than letting it enter the sensitive circuits of your equipment.

Voltage spikes can come through the power line and or through the telephone line. So phone lines need to be protected too, if connected to your equipment.

Under normal conditions electric lines have a steady voltage (120 volts in the United States). But in some cases erratic fluctuations of the voltage can occur. These are spikes in the electric power that can damage equipment.

Any voltage spikes need to be re-channeled to ground. This is what a surge protector does.

Where Do Power Surges and Voltage Spikes Come From?

Lightning is well known for creating power surges. But voltage spikes can also come from high powered equipment that is on the same circuit. These can create powerful spikes, in the electric line when they are turned on and off.

For example, if you have a refrigerator or air conditioner on the same line as your computer, you may very well be getting interference that can damage the computer. Sometimes it might just be an unexpected reboot. But it can also cause hard disk crashes that cannot be recovered.

The average surge protector will not protect your equipment from lightning strikes. If this is a major problem in the area where you live or work, then you need to consider a full-building protection with an external lightning arrestor that diverts lightning strikes to ground.

If this is your concern, check with your power company and your telephone company. Ask what precautions they have taken to protect you and what recourse you have in case their lightning protection fails.

Clamping Voltage vs. Joules

What do you look for to select a good surge protector?

You need to pay attention to two things:

  • Clamping voltage - needs to be low to cut off high voltages.
  • Joules - needs to be high to increase the surge protector's life expectancy.

You want a low clamping voltage. This is the amount of voltage that is let through. You don't want to let through too high a voltage, as it will blow your equipment.

The standard clamping for a 120-volt line is 330 volts. Don't buy anything that lets more than that through.

You also want a protector that can absorb as much energy as possible before blowing itself out. This is measured in joules. The higher this number, the longer will be the life expectancy of your surge protector.

If this absorption rate is too low, you may only be protected for a single event. Then you need to get a new surge protector. This is another mistake many people make. They don't realize that the surge protector is not going to protect them indefinitely.

How Many Joules Do You Need for Good Surge Protection?

You want to protect your equipment, but you also don't want to keep buying a new surge protector each time they protect you.

If you use one that has a really high joule rating, then it should last through many power surges and spikes.

I suggest a rating over 3000 joules. Anything less and your surge protector may not survive a spike. Your equipment may not be protected if you get more than one high voltage spike before replacing the surge protector.

Surge protectors that have a low joule rating may be destroyed by a single high voltage spike. These cheap protectors need to be replaced often. You end up saving more money in the long run by getting a good surge protector joules rating to begin with.

What Is a Good Recommended Surge Protector?

I use the APC Back-UPS XS 1000 Uninterruptible Power Supply (UPS) on my main office computer where I need to avoid losing power. Many UPS's have surge protectors built in, such as this one. If you don't require guaranteed power without interruption, then a surge protector is all you need.

There are a number of good manufacturers, such as Belkin, Tripp Lite, and APC. Some surge protectors have LED lights to indicate that it is working and that you are protected.

The most important ting to remember is to pay attention to the joules (the higher the better) and the clamping voltage (basically around 330 volts).

3570 Joules of surge protection for power and phone lines:

Tripp Lite Isobar 10 Outlet Audio/Video Surge Protector Tel/Modem/Coax/Network 8ft Cord Right Angle Plug (HT10DBS)
Tripp Lite Isobar 10 Outlet Audio/Video Surge Protector Tel/Modem/Coax/Network 8ft Cord Right Angle Plug (HT10DBS)

You can also find power strips with surge protection. I use the Tripp Lite HT10DBS Isobar. It has 10 Outlets and enough room to plug in a few large transformer adapters, as shown in the image.

You will also want to include surge protection on your phone lines, if they are connected to your equipment. The Tripp Lite Isobar includes protected phone line jacks.

Another solution is to have the phone company install surge protection on each phone line coming into your premises.


Whole-House Surge Protection for All Electronics

All your electronic devices should be protected. If you have a lot of different equipment thought your home, you may want to consider a whole house surge protector. This needs to be installed by an electrician.

This could help save everything else that wouldn't have been protected otherwise. Besides damage from lightning strikes, voltage surges from other sources can come through your electrical system too. You never know where it strikes and protecting your entire home is the best choice when you have many expensive things.

As a final thought, it's not just power surges that can cause damage. Computers can experience problems not related to a power surge, such as a hard disk crash. So don't forget to back up your data.

Questions & Answers

    © 2010 Glenn Stok

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      • Glenn Stok profile image

        Glenn Stok 7 months ago from Long Island, NY

        Jordan, When you turn on a heavy-usage device there is an initial spike that can reach close to 330 volts. If the clamping voltage were any lower, the surge protector would erroneously trip every time you turn on the device.

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        Jordan 7 months ago

        Thanks for your response Glenn, but I admit I am still in the dark with the 330v UL Let thru limit. I know about the lesser the better, so why so high ? I would have thought something like 110 volts would be ideal / best let-thru voltage vs 330v. Plus I think the clamping voltage should ideally be like 130v max. What do you think ?

      • Glenn Stok profile image

        Glenn Stok 7 months ago from Long Island, NY

        Jordan - You need to compensate for normal spikes when a unit is turned on. The lowest UL rating for clamping voltage is 330 volts. The lower the rating, the better the protection.

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        Jordan 7 months ago

        A UL rating of 330 volt ? Isn't that too high for let thru ? Clearly I am missing something here with UL standard.

      • Glenn Stok profile image

        Glenn Stok 6 years ago from Long Island, NY

        Frank, If they don't provide the information you need to make a purchase decision, then don't buy the product. That's their lose if they don't have complete specs, or they are hiding something about an inferior product. There is no way I can determine that.

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        Frank in Miami 6 years ago

        Good site, thanks for helpful info so far.

        I wanted to purchase a new surge suppressor for my HTIB setup, but have had difficulty determining anything except protection in joules -manufacturers seem to not -or not WANT to -include either clamping voltage or response time in the specs, either on the box or online. I went with a Dynex DX-S114241 11-outlet model, with a 3750 joule protection rating. Know anything about clamping voltage or response time for this model?

        Thanks in advance.

      • Glenn Stok profile image

        Glenn Stok 6 years ago from Long Island, NY

        LH Fernando, Clamping voltage is the level where electricity will be conducted to ground in order to protect your device. So you want to have a clamping voltage as low as possible which is still over the level of you normal highest voltage.

        The lowest UL protection rating is 330 volts. Your highest voltage during ringing is 150, so get a 330 rated clamping voltage.

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        L.H.Fernando 6 years ago

        Our (Sri Lanka) telephone system has 48 V DC supply when "on hook" and 130-150 V (rms)during ringing. What would you suggest for the clamping voltage of the SPD for the telephone line?