How Many Joules of Surge Protection Do You Need?

By SB •  Updated: 08/30/21 •  11 min read

Joules are measurement of energy. For example, 1500 joules is like leaving a 1500 watt hair dryer on for one second. A surge protector with a joules rating of 3000 for example, will “absorb” energy surges of up to 3000 joules. If your electronics are sensitive to energy surges, you will want a surge protector with a high joules rating and a low clamping voltage.

A decent surge protector rating for home electronics is at least 600 joules, and here’s why:

What to look for when choosing a surge protector

On a UL-listed surge protector, you should find a couple of Underwriters Laboratories (UL) ratings. Do not choose a surge protector that does not have a UL listing; it is probably junk and little more than a power strip.

Be sure that the product is listed as a transient voltage surge suppressor. This means that it meets the criteria for UL 1449, UL’s minimum performance standard for surge suppressors. There are a lot of power strips listed by UL that have no surge protection components at all. They are listed only for their performance as extension cords.

Look for:

How surge protectors work

Various factors can cause a brief increase in voltage:

If the surge or spike is high enough, it can inflict some heavy damage on your home electronics. The effect is very similar to applying too much water pressure to a hose. If there is too much water pressure, a hose will burst. Approximately the same thing happens when too much electrical pressure runs through a wire — the wire “bursts.” Actually, it heats up like the filament in a light bulb and burns, but it’s the same idea. Even if increased voltage doesn’t immediately break your machine, it may put extra strain on the components, wearing them down over time.

So, what do surge protectors do to prevent damage from power surges?

A standard surge protector passes the electrical current along from the outlet to a number of
electrical and electronic devices plugged into the power strip. If the voltage from the outlet surges
or spikes — rises above the accepted level — the surge protector diverts the extra electricity into
the outlet’s grounding wire.

As soon as the extra current is diverted into the MOV and to ground, the voltage in the hot line returns to a normal level, so the MOV’s resistance shoots up again. In this way, the MOV only diverts the surge current, while allowing the standard current to continue powering whatever machines are connected to the surge protector. Metaphorically speaking, the MOV acts as a pressure-sensitive valve that only opens when there is too much pressure.

In the most common type of surge protector, a component called a metal oxide varistor, or MOV, diverts the extra voltage. An MOV forms a connection between the hot power line and the grounding line.

When to use a surge protector

Microprocessors, which are an integral part of all computers as well as many home appliances, are particularly sensitive to surges. They only function properly when they receive stable current at the right voltage.

So whether or not you should get a surge protector depends on what sort of device you’re hooking up to the power supply.

There’s no reason to hook up a light bulb to a surge protector because the worst that is likely to happen due to a power surge is that your light bulb will burn out.

You should definitely use a surge protector with your computer. It is filled with voltage-sensitive components that a power surge could damage very easily. At the least, this damage will shorten the life of your computer, and it could very easily wipe out all of your saved data or destroy your system.

Computers are very expensive items, and the data they hold is often irreplaceable, so it’s only good
economic sense to invest in a quality surge protector.

It’s a good idea to use surge protectors for other high-end electronic equipment, such as entertainment center components. A surge protector will generally extend the life of these devices, and there’s always a chance that a big power surge will causes severe damage.

One problem with surge protectors is that the MOVs can burn out with one good surge. This is why it’s good to get a protector with an indicator light that tells you whether or not it’s functioning properly.

Even if you connect surge protectors to all of your outlets, your equipment might be exposed to damaging surges from other sources. Telephone and cable lines can also conduct high voltage –> modem, you should get a surge protector that has a phone-line input jack. If you have a coaxial cable line hooked up to expensive equipment, consider a cable surge protector. Surges on these lines can do just as much damage as surges over power lines.

Consider the following guidelines: Line voltage surges are not always a “one-shot” experience, they have an accumulative effect, and result in the premature death of many electronic devices.

1. The surge protector not only protects the devices plugged into it, but it also protects itself from being damaged. The joule rating is how much excess energy the device can withstand before frying from electrical damage. Once fried from a surge larger than its joule rating, it no longer protects anything.

2. Clamping voltage: The joule rating is only half of the protection story — the other rating is the clamping voltage, which is at what over-voltage the protector begins to work. If not listed in the specs, then the rating is likely not useful. A lower clamping voltage indicates better protection. There are three levels of protection in the UL rating — 330 volts, 400 volts and 500 volts. Generally, a clamping voltage of more than 400 volts is too high to be useful.

3. The clamping voltage (rated in “voltage peak”) of your surge protector should be 330 volts or less. This is the minimum voltage at which protection will begin. (That’s approximately twice the normal line voltage). 400 volts is marginal and 500 volts is too much after the damage may be done.

4. The absolute minimum joule rating for anything you want to protect is 600 joules. However, for anything really valuable, opt for 3000 joules of protection or more. This rating number is the sum of protection for all three legs (hot to neutral, hot to ground, neutral to ground), thus any one leg is only protected at one third of the specified “joule” rating.

In brief, choose a surge protector rated at 600 joules or higher (energy absorption), and 330 volts or less (of clamping voltage).

Make your own assessment of how much surge protection you need before you invest.

Lightning generates up to 10 billion joules of energy (watts per second). Wowza.

Is the higher the Joules rating, the better the protection?

In brief, the higher the joules rating the better, as more joules mean the surge protector is made to absorb one large surge to capacity or many smaller surges, before your electronics protected by the device are in any danger.

It is important to choose a surge protector with a higher joules rating than you need because over time and use the parts inside the protector wear down, thus reducing its surge protectiveness. Never buy a surge suppressor that does not have UL and ISO stickers on it. The ISO labels are holographic so they cannot be copied and used on cheap and dangerous rip-offs.

How many joules are adequate for a surge protector?

If you are protecting expensive electronic equipment such as a computer or home entertainment system that costs a lot to replace, opt for the highest rating in joules protection that you can afford — at least 3000 joules.

A surge, sometimes called a transient or a spike, is a brief burst of energy (voltage and current). The most damaging surges enter through your home’s power, cable and telephone lines. However, the majority of surges originate within the home from the action of motor-based appliances like dishwashers, refrigerators, garage door openers, etc.

While any device that gets plugged into an AC outlet can benefit from surge protection, inexpensive or easy-to-replace electronics such as lamps, digital clocks, blenders, streaming boxes or other small devices do not need a high level of protection.

The surge device protects your equipment from damage from incremental or sudden power surges, so the higher the value of your equipment, the higher the surge protector joule rating you will want.

How many joules of surge protection do you need?

A surge suppressor unit rated up to 1000 joules of surge protection is adequate for equipment such as a router or old TV that does not store important data. Some electrical components in your devices will have sensitive circuitry requiring protection, but a basic guidance is to have a surge protector with a rating of 1000 to 2000 joules of protection for power tools, printers, copiers, and routers.

Does a TV need a surge protector? Consider the advice to choose the highest joules rating (3000 +) for expensive items that are hard to replace: home theatre components, expensive gaming consoles, network storage or computers that store important data or data which cannot be replaced.

How many joules are needed to protect a mac laptop, pc computer, TV, or washing machine?

DeviceRecommended Minimum Joules Rating for Surge ProtectorMinimum Clamping Voltage
Laptop2000330 volts
Desktop3000330 volts
Router2000330 volts
TV3000330 volts
Washing Machine1000-2000330 volts
Raspberry Pi2000330 volts

How long does a surge protector last?  

The joule rating can be compared to a finite store of protection: each surge of electricity will withdraw some amount from the protection store.

Surge protectors do not display how many joules of protection are available, but most models include an LED that indicates the protection is “on”.

The joule rating is how much energy the surge protector can “absorb” before it sends the remaining energy to your connected devices. In general, the higher the joule rating, the better. The protection you gain is from the surges that come through your electricity provider; it is unlikely that ANY surge protector will protect against a lightning strike spike (the amount of energy is huge). Is connecting several surge protectors together safe to do, and will it increase the clamping voltage?


I've been practicing OSINT and utilizing Linux as my daily operating system for over twenty years. The tools are always changing and so I'm always learning, but helping you understand the value of protecting your own data remains at the forefront of everything I do.