Cascaded Power Surge Protection

Poor quality electricity is detrimental to the life of electronic equipment. Computers, laptops, TV’s, stereo systems, in fact anything with electronics in it, are susceptible. Fluctuating voltages, frequencies and current all reduce the life of electronic equipment, bringing forward unnecessarily the repair or replacement date. Dealing with power quality issues is a subject for another blog, in this article we focus on power surges.

Power surges can occur when the mains supply experiences an overload, sometimes from a fault at the generating station, transformer or from a lightning strike. It can even be from equipment inside your office or facility.  A power surge is very short (measured in milliseconds) but the amount of power released is enormous and has a catastrophic impact on any electrical equipment connected to the mains. Although the surge event can be more than 20,000 volts, it is so short that it will not trip a breaker.  In the event of a lightning strike power can also be transmitted through telephone and cable TV lines with the same result – end equipment destroyed beyond repair.

So what can you do about it? Well, protect your equipment through cascaded Surge Protection. This means using two or three levels of protection as described below.

About Surge Protection Devices

Before we talk about cascades, a brief note about Surge Protection Devices (SPDs).  They are rated in KA (KiloAmps).  That basically indicates the level of protection the device provides.  The higher the KA rating, the more surges it will take before failing.  All quality SPDs will come with indicator lights that give the status of protection from the SPD.  They will come with a light on each “phase” or line of the incoming power.  So you would expect to see 2 or 3 lights (1 if for single phase only). They are usually green when protecting the equipment and turn red when their self-sacrificial components (usually MOVs) are depleted.

Level One Cascade

Level one is the surge protection device (referred to as Type 1) you should have installed where your main power source enters your property (Service Entrance).  This device is designed to protect your property from electrical power surges, and for lower voltage surges it may be adequate. The problem is that with a major power surge such as a lightning strike, some of the surge will still make it through to your power outlets (called “let through”). Something of the order of 7,000 volts or more can pass. Consider that your electronic devices are usually designed to run with 12 volts or less and the problem is clear. This is why a second level of protection, or a “cascade”, is recommended.

Level Two Cascade

At level two we recommend using a Type 2 SPD.  It can be mounted anywhere downstream of the Type 1.  This is commonly located at a Distribution Panel. 

Level Three Cascade

Level Three can be a variety of smaller SPDs, from Residential SPDs with a lower KA rating, or even a Surge Strip.  A good quality Surge Strip should also have inputs and outputs for telephone lines and cable TV. These SPD strips therefore provide additional protection from power surges and the convenience of multiple outlets.

Another device to consider for Third Level Protection is a UPS. Many people still think of a UPS as a backup power supply, which of course they are. However, modern UPS devices have many features, including:

  • Power quality improvement, that is smoothing the voltage, frequency and current being output to your devices
  • Power backup, usually for a few minutes giving you time to conduct an orderly shutdown of equipment when the mains power fails
  • Surge protection. Yes, a UPS has built in surge protection so you can further reduce the size of an electrical surge reaching your devices. Unfortunately many UPS do not indicate whether their SPDs are still protecting your equipment, so they should be used as the last level of SPD protection.

With this in place you now have a well-protected system.


Cascaded surge protection provides the best approach to ensuring the longevity and protection of your computing, TV and electrical devices. If you follow the three level cascade outlined above, you will also enjoy additional benefits including better power quality, backup power and multiple outlets for several devices.  Contact your local Power Quality Supplier (Parts & Power in the BVI) to discuss the products that are available, and the KA ratings that you will need.


About partsandpower

Parts & Power is the premier supplier of Marine and Industrial equipment and spare parts in the Caribbean.

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