How Many Joules of Surge Protection Do You Need?


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.

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 2000 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 3000 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 lower the “stored protection” (joule rating), the more quickly it will be depleted and the more often you should replace the surge protector.
  • No surge protector lasts forever. If you’ve had a major electrical event, such as lightning that caused a power failure, or if your units have been in use for a few years, the coverage of surge protection may be exhausted.
  • If you can, to almost guarantee protection against lightning strikes, unplug the surge protector from the wall outlet when not in use.

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?

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