How to Protect Your Electronics From Electrical Surge Events


In this modern world, we have become very dependent upon our electronic gadgets. We use personal computers to work, communicate with friends, family members or business associates.

We often times store valuable files (such as financial documents, memos, reports, *.mp3 files, and now we also store important personal pictures) onto the Hard Drives of our Computers.

We use the following electronic systems to entertain, educate, enlighten and comfort us.

  • DVD Players
  • HDTVs (e.g., LCD and Plasma)
  • Video Recording Equipment (for those of you upload your videos on to YouTube)
  • Gaming Systems (e.g., Nintendo, Wii, X-Box, etc.)
  • Central Air Conditioning System, Heat Pumps
  • Microwave Ovens

These and other electronics gadgets require a significant investment to obtain in the first place; and are very expensive to repair and/or replace.

And yet, amazingly, we do very little to protect our electronics from damage or attempt to make them last (and serve us) longer.

This article is one of a series of three (3) articles that discusses how to protect your electronics against the following destructive mechanisms that shorten its operating life.

Electrical Surge/Spike Events, and
Electrical Noise

In this particular article, we are going to talk about “Electrical Surge/Spike Events”.

In particular, we are going to discuss the following topics associated with “Electrical Surge/Spike Events”.

What are Electrical Surge/Spike Events and How are they generated?

How do you protect your electronics from Electrical Surge/Spike Events?

What are some guidelines that you should use when selecting a Surge Protector?


Electrical Surge/Spike events are typically defined as a “large current/voltage transients that occurs in an electrical signal or the power-line”.

Surge events typically last for a few microseconds and are then gone. Similarly, spike events will typically last for a few nanoseconds and are then gone.


a. 1 microsecond = 1 millionth of a second, and
b. 1 nanosecond = 1 billionth of a second.

Both electrical surge and spike events can cause considerable damage to any electronic systems that are electrically connected to these power-line or signal-lines that are carrying this transient current and voltage.

For a typical person that lives in a home and own some consumer electronics, electrical surge/spike events can fall into one of two categories.

External Surge/Spike Events, and
Internal Surge/Spike Events

I will briefly define each of these types of Surge/Spike events below.


External Surge/Spike events are called “External” because they occur “External” to (or outside of) your home.

External Surge/Spike events typically originate from one of two sources.

Lightning Strikes (during an Electrical/Thunderstorm), and
Switching events within the Electrical Grid

External Surge/Spike events tend to be very large and damaging (especially if they originate from lightning strikes).

If these external surge/spike events were to enter your home (via the main power line and through the circuit breaker panel), they will destroy pretty much any piece of electronics that is connected to an electrical outlet in your home.

NOTE: These pieces of electronics do not need to be powered on to be destroyed.

They only need to be plugged into an outlet in your home at the time when this catastrophic electrical surge/spike event occurs.

Fortunately, the External Electrical Surge/Spike events do not occur very often (e.g., a few times a year depending upon what part of the world you live in).


Internal Surge/Spike Events (as the name implies) are generated “internal” (or within your home).

Internal Surges/Spike events typically occur whenever the motor or an appliance (such as an Air Conditioner or the Refrigerator turns ON or OFF).

Internal Surge/Spike events tend to be much smaller than External Surge/Spike events.

However, Internal Surge/Spike events occur much more often than do External Surge/Spike events (several times a day).

Over time, these smaller (though more frequent) internal surge/spike events will do damage to your electronics as well.

Each time a motor of an appliance (such as an Air Conditioner or a Refrigerator) requires surge current (for it to turn on), or anytime the magnetic field (within the motor of an appliance collapses) whenever it is turned OFF, a damaging surge or spike is generated and can propagate throughout some of the power supply lines in your home.

Internal surge events will shorten the operating life of any electronic gadget that is plugged into an electrical outlet in your home.

NOTE: The electronics gadget does not need to be powered ON for it to sustain some damage from these internal surge/spike events.


One of the most common ways of protecting many of your electronics from damage (due to electrical surge/spike events) is through the use of “power strips” that contain “surge protection” circuitry within them.

Many power strips have surge protection built in, and in most cases, these types of power strips are clearly marked to reflect this.


There are some power strips that do not provide surge protection for your electronics.

Often times, people will still (incorrectly) refer to these products as “surge protectors”.

If you are looking to purchase a Power strip that contains “Surge Protection” circuitry, make sure that the labeling (on the box that you have in your hands) clearly indicates “Surge protection” or something like that.

If you cannot quickly find those words on the box, then I recommend that you put that Power-Strip box back on the shelf and go find a Power-Strip that has “Surge Protection” clearly marked on it.


Surge Protector circuitry typically works by having devices (like an MOV – Metal Oxide Varistor) that “sits” between the “power-line” path and electrical ground within the power strip.

Many Surge Protectors will have several of these MOV devices in order to make them more robust.

Under normal operation, these MOV devices will do nothing at all and do not affect the operation of your appliances or electronic systems.

For you electrical engineers out there, I will tell you that these MOV devices presents a very high impedance between the “power-line” and “electrical ground”.

If a surge event occurs such that the “power-line voltage” exceeds a certain “threshold” voltage level, then the MOV devices will start to conduct current (and will then present a very low impedance path) between the “power-line” and “electrical ground”.

At this point, all of this excessive energy (from the electrical surge event) will be “routed” through the MOV devices (to electrical ground) and will be diverted away from your valuable electronics.

Once the “power-line voltage” returns to a normal level, the MOV devices will then return to their “high-impedance” state and will cease to conduct current between the power-line and electrical ground.


In general, you should use surge protectors on all sensitive electronics that you would like to keep and use for some period of time.

If you have Surge Protectors for each of your sensitive electronics, then they will do a very good job protecting your electronics, for the duration that they (the Surge Protectors) function.


In general, you should look for the following parameters/metrics whenever you are shopping around for Surge Protectors.

Clamping/Let-Through Voltage
Joules Rating
Response Time (if available)

I will explain each of these items below.

3.3.1 Clamping Voltage:

The “Clamping Voltage” level is also (often times) referred to as the “Let-Through Voltage” level.

Basically, this is the voltage level that will cause the MOVs (inside the Surge Protect system/Power-Strip) to conduct electrical current between the “power-line” and Electrical Ground.

At this voltage level, the Surge Protector will start to shunt the destructive electrical energy (from an incoming surge event) to Electrical Ground and will divert it away from your valuable electronics.

As I mentioned before, the MOVs will continue to shunt electrical current (from the power line) to Ground for the duration that the “Power-Line Voltage exceeds this “Clamping” or “Let-Through” Voltage level.

In general, the lower the “Clamping” or “Let Through” Voltage level the better the protection for your electronics.

Typical values for “Clamping” or “Let Through” voltage level are 330V, 400V, or 500V.

For 120V AC applications, I recommend that you use a Surge Protector with a Clamping Voltage level of 330V.

3.3.2 The Joules Rating

The “Joules” Rating for a Surge Protector will typically define the cumulative amount of energy that it (the Surge Protector) can absorb (throughout its operating life-time) without failing.

In general, the higher the number, the longer the Surge Protector will last and continue to protect your electronics.

Good Surge Protectors are ones that have a “Joules Rating” of 1000J or better.

NOTE: The “Joule” Rating does not reflect the total amount of electrical energy that the Surge Protector will shunt (to Electrical Ground) before failing.

The “Joule” Rating reflects the amount of energy that the components (mostly the MOVs) within the Surge Protector can absorb without failing.

In most cases, whenever an MOV shunts excessive voltage and current to ground (during a Surge Event), it (the MOV) is only absorbing a fraction of this energy.

Most of this energy is “being dumped” to Electrical Ground.

If your Surge Protector is properly installed, then for every joule absorbed by the components (inside the Surge Protector) another 4 to 30 joules was harmlessly shunted from the Power-line to Electrical Ground.

However, each time your Surge Protector responds to a surge event, the MOV devices do absorb some energy, and the cumulative amount of energy that these devices have absorbed moves closer and closer to the “Joules Rating” number and “failure”.

3.3.3 Response Time

Surge Protectors do not respond immediately to Surge Events.

There is a slight delay (or response time) before they respond.

The longer this response time, the longer your electronics sits exposed to the incoming surge event. Fortunately, most surge events do not happen immediately either. Most surge events take several microseconds before they reach their peak voltage.

By that time, most Surge Protection schemes (especially those using MOVs) will “kick in” within nanoseconds after the voltage level has exceeded the “Let Through” Voltage.


Just like the smell of a brand new car, Surge Protectors do not last forever.

As these MOVs respond to Surge Events and “shunt electrical energy to ground” over time, they absorb some of that energy.

This process causes “degradation” and “wear and tear” on the MOV devices (and in-turn) on the Surge Protectors as a whole.

Eventually these MOVs will fail in one of two ways.

a. The MOVs will fail to the point that they will no longer shunt excessive electrical energy to ground. In this case, the MOVs (are said to fail in an “Open” state).

Whenever this occurs, all of your precious electronics that is “downstream” from your Surge Protector are now “officially” un-protected and are now vulnerable to the next surge event that comes around.

b. At least one MOV device will fail into a “Short Circuited” Mode. In this case, the MOVs may (though rarely) fail in the “Short Circuit” state.

Whenever this happens, the “failed” MOV device would continue to conduct high currents (from the Power-line to Electrical Ground) even when the power-line voltage is less than the “Let Through” voltage.

This type of failure mode could be very dangerous.

Fortunately, most Surge Protectors will typically have a fuse that will “blow” and will turn OFF the Surge Protector entirely, rather than risk catching on fire.

The main message here is this. Internal Surge Events occur many times throughout the day.

As these events occur, and as your Surge Protectors continue to function and shunt the excessive electrical energy to ground, these Surge Protectors eventually wear out and will need to be replaced.


You should replace your Surge Protectors under the following conditions.

1. Whenever the Green “Protected” Light (on the Surge Protector itself) goes OUT.

2. If you’ve owned your Surge Protector for more than 3 years.

NOTE: Having the Green Light ON is encouraging but is not a guarantee of adequate protection for the next surge events.

Replacing your Surge Protectors every three years is a good practice to keep your electronics protected.


In this article we have discussed one of the three main enemies of electronics and how they shorten the operating life of electronics and cost you money.

Other articles in this series are listed below.

How to Protect Your Electronics from Heat, and
How to Protect Your Electronics from Electrical Noise