These operate to switch electric circuits and equipment in and out of the system. These circuit breakers are filled with compressed sulfur-hexafluoride gas which acts to open and close the switch contacts
US Department of Labor, Electric Power eTool: Glossary of Terms, Occupational Safety & Health Administration OSHA, Washington, D.C., USA 2010. https://www.osha.gov/SLTC/etools/electric_power/gl ossary.html, (OSHA/ Electr Pwr - Amer) {618}