Our History

Innovation is the heart of SEL.

Inspired by his research as a doctoral candidate, Dr. Schweitzer invented the first microprocessor-based digital protective relay, the SEL-21, which revolutionized the electric power industry and provided new functionality in power system protection. He made his first sale to Otter Tail Power Company in 1984.

The grit, passion, and creativity that drove SEL from a basement with a handful of employees to a worldwide company with over 5,000 employees continue to be a driving force and source of inspiration today.

Timeline of Events


Dr. Schweitzer founds Schweitzer Engineering Laboratories with the invention of the SEL-21, the first relay to use microprocessor-based computation and algorithms.


SEL makes its first sale to Otter Tail Power Company in Fergus Falls, Minnesota, as a company of seven working out of Dr. Schweitzer’s basement.


SEL grows to 100 employees.


SEL implements the employee stock ownership plan (ESOP).


We release the SEL-351, which became the benchmark for protective relay standards in North America.


SEL begins offering engineering consulting, testing, and design through our Engineering Services team.


We introduce our unprecedented ten-year, worldwide product warranty—the best in the industry.


SEL establishes Government Services to serve government customers.


SEL opens a site in Monterrey, Mexico, to manufacture high-quality panels for our customer Comisión Federal de Electricidad.


SEL acquires E. O. Schweitzer Manufacturing in Mundelein, Illinois, which was started by Dr. Schweitzer’s father, Edmund O. Schweitzer, II.


SEL becomes 100 percent employee-owned.


SEL opens a manufacturing facility in Lewiston, Idaho.

We kick off the first year of our Modern Solutions Power Systems Conference, which encourages cross-disciplinary discussion of common challenges and success stories relating to electric power and promotes idea generation to drive innovation.


We introduce the SEL-T400L Time-Domain Line Protection, the fastest relay in the world.


SEL President and Chief Technology Officer Dr. Edmund O. Schweitzer, III, is inducted into the National Inventors Hall of Fame for his invention of the microprocessor-based digital protective relay.


We open the doors to our fifth manufacturing facility, next to Purdue University in West Lafayette, Indiana. The site’s proximity to Purdue University allows close research collaboration between the two entities.