Print this page Print this page

Secondary Surge Protection

Lee Layton, P.E.

Course Outline

The course begins with an overview of lightning, how lightning occurs, and an example of a typical lightning event.  From this beginning, transients are explained and how they impact residential equipment.

Next, transient voltage surge suppression devices are discussed, including the characteristics of SPDs and the types of SPDs available.

The standards that are applicable to SPD equipment, as well as the equipment it is protecting, are reviewed including IEEE C62.41 and the “CBEMA curve”.

Finally, a typical residential application is reviewed along with how the home might be protected.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

After taking this course you should,

Intended Audience

This course is intended for electrical engineers, and others who want to more about minimizing the impact of electrical surges in residential and small commercial applications.

Benefit to Attendees

Taking this course will give you a better understanding of how lightning and other overvoltage conditions affect consumer and small business appliances and equipment and how to design a system to minimize the impact of surges.

Course Introduction

From an electric utility perspective, secondary surge protection means protecting the secondary of a distribution transformer from damaging overvoltage conditions.  From a residential consumer’s perspective, secondary surge protection concerns mitigating the effects of over-voltages on appliances, computers, and other household electrical appliances. 

The sophistication of computer controlled equipment found in homes today rivals the processing capability of business computer centers just a few short years ago.  And these business computer rooms had special requirements for “clean” power whereas the typical residential home is exposed to all types of varying voltage conditions that can harm equipment.

Suppression includes methods to control spikes and transients.  For our purposes we will define a spike as a short-term overvoltage condition of less than two per-unit of the normal voltage and a transient surge as any short-term overvoltage in excess of two per-unit.  Regulation involves keeping sags and swells within acceptable limits.  A swell is an increase in voltage, at the power frequency, for durations from one-half cycle to one-second.  In contrast, sag is a reduction in voltage, at the power frequency, for durations of one-half cycle to a one-second.  Harmonics are integer multiples of the fundamental power frequency and are caused by non-linear loads such as switching power supplies, etc.  Noise is a low-energy random signal that appears on the voltage or current wave.  Noise may be caused by fluorescent ballasts, door bell transformers, electric heating elements, etc.

The most common form of secondary voltage condition is a transient surge followed by spikes and over/under voltage conditions.  The combination of spikes and surges total 88% of the typical power line disturbances.

Course Content

This course content is in the following PDF document:

Secondary Surge Protection

Please click on the above underlined hypertext to view, download or print the document for your study. Because of the large file size, we recommend that you first save the file to your computer by right clicking the mouse and choosing "Save Target As ...", and then open the file in Adobe Acrobat Reader. If you still experience any difficulty in downloading or opening this file, you may need to close some applications or reboot your computer to free up some memory.

Course Summary

Every year thousands of dollars of consumer equipment is damaged from surges.  Not only is sensitive electronic equipment at peril, but common appliances such as microwaves, heat pumps, garage door openers, and well pumps are frequently destroyed by surges.

While transient conditions that damage equipment are hard to quantify, manufacturers have agreed on a common set of standards to test the capability of their protective devices.  Adherence to standards such as UL 1449 may give consumers some comfort that the surge protection device will provide a quantified level of protection.

Protecting electrical equipment in a residential application involves ensuring that a proper grounding system is in place and that service entrance protection is provided as well as individual protection at each point-of-use.  Lastly, consumers need to understand that surge protection involves a degree of luck, because the magnitude of some surges is so severe that no amount of surge protection will protect the equipment.


Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.