A Closer Look at Onsite System Control Boxes

A Closer Look at Onsite System Control Boxes

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Author’s note: Be sure all electrical work is done by the appropriately licensed professional required in your jurisdiction. Often septic system installers must work with electricians to understand the needs of the system being installed.

Outdoor equipment used in residential wiring must be weatherproof. The two most common types of weatherproof equipment are driptight and watertight.

  • Driptight equipment seals against water falling vertically. Driptight boxes are usually made of painted sheet metal and have shrouds or shields that deflect rain falling from above. These boxes are not waterproof and should not be used where water can spray or splash on the unit. Driptight boxes are usually used for control or circuit breaker panels.
  • Watertight boxes seal against water coming from any direction. Individual junction boxes, switch boxes and receptacle boxes will usually be of the watertight type. Watertight boxes are designed to withstand temporary immersion or spray streams from any direction. They are commonly made of cast aluminum, zinc-dipped iron, bronze or heavy plastic, and have threaded entries for watertight fittings and covers sealed by gaskets.

In all cases, electrical components and connections must be properly protected from the elements and from the corrosive environment of the dosing tank. Ideally, this is achieved through use of a National Electrical Manufacturers Association rated box with properly sealed connections. NEMA ratings are standards that are useful in defining the types of environments in which an electrical enclosure can be used. The NEMA rating system is defined by the National Electrical Manufacturer Association, and frequently signifies a fixed enclosure’s ability to withstand certain environmental conditions. 

In nonhazardous locations, there are several different NEMA ratings for specific enclosure “types,” their applications, and the environmental conditions they are designed to protect against, when completely and properly installed. The following provides an overview of the NEMA types. For complete definitions, descriptions and test criteria, see the NEMA Standards Publication No. 250.

NEMA Type Application
NEMA type 1 Type 1 enclosures are intended for indoor use, primarily to provide a degree of protection against contact with the enclosed equipment in locations where unusual service conditions do not exist.
NEMA type 3R Type 3 enclosures are intended for outdoor use, primarily to provide a degree of protection against windblown dust, rain, sleet and external ice formation.
NEMA type 4 Type 4 enclosures are intended for indoor or outdoor use, primarily to provide a degree of protection against windblown dust and rain, splashing water, and hose directed water and external ice formation.
NEMA type 4X nonmetallic, corrosion-resistant Type 4X enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against corrosion, windblown dust, and rain, splashing water, and hose-directed water. Enclosure is manufactured with a synthetic rubber gasket between cover and base. This is ideal for such industries as chemical plants, paper mills and septic systems.

NEMA 4 or 4X with properly sealed connections are the most referenced types in septic system installation.  

About the author
Sara Heger, Ph.D., is a researcher and educator in the Onsite Sewage Treatment Program in the Water Resources Center at the University of Minnesota, where she also earned her degrees in agricultural and biosystems engineering and water resource science. She presents at many local and national training events regarding the design, installation and management of septic systems and related research. Heger is the President of the National Onsite Wastewater Recycling Association and she serves on the NSF International Committee on Wastewater Treatment Systems. Ask Heger questions about septic system design, installation, maintenance and operation by sending an email to kim.peterson@colepublishing.com.


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