New Industry Products

Substation Circuit Breaker Earns NEMA 4 Rating For Water, Dust and Weather Resistance

June 17, 2023 by Mike Falter

The new housing for ABB’s R-MAG magnetic outdoor vacuum circuit breaker has received a 4 rating from the National Electrical Manufacturer Association for its reliability under adverse weather conditions–sleet, snow, dust storms, and wind-driven rain.

ABB has announced a highly coveted four-star rating from the National Electrical Manufacturers Association (NEMA) for the new housing of their R-MAG outdoor vacuum circuit breaker. 


R-MAG vacuum interrupter circuit breaker deployed at a substation

R-MAG vacuum interrupter circuit breaker deployed at a substation. Image used courtesy of  ABB

The new housing is designed to withstand the most adverse weather conditions, including sleet, snow, dust storms, and wind-driven rain, at rates of up to 65 gallons per minute, ensuring continuity of power for grid customers.   

The new housing is available for medium voltage (MV) breaker units rated to 15, 27, and 38 kV, supporting up to 3,700 A of continuous current.


Designed for Grid Resilience

According to ABB, extreme weather conditions such as flooding, heat, and drought continue to impact the energy security of millions of energy consumers across the globe, causing billions of dollars of economic losses each year. Responding to the demand for power delivery infrastructure that can operate with resilience and reliability in the face of severe weather conditions, ABB has designed its next-generation, weather-resistant breaker housing to meet stringent NEMA 4 standards for water and dust ingress.  

The housing is designed for ABB’s R-MAG magnetically actuated dead tank breaker for MV primary substations. Key to meeting NEMA 4 standards is a design featuring seamless roof-to-wall joints and self-sealing external bolts that prevent any water, dust, or materials from entering the breaker housing. A simple roof overhang helps protect the sides of the breaker from water exposure. Aerospace-grade, UV-resistant gaskets ensure a watertight seal between the housing and bushings interface where electricity passes into and out of the enclosure.  


Arc-Resistant Housing

In addition to the weather-resistant housing, ABB is releasing an arc-resistant housing variant for the R-MAG breaker. The design of the arc-resistant housing ensures that gasses or fire resulting from an arc fault condition are properly expelled from the unit. The design also offers additional safeguards for power station personnel and facilitates faster restoration from a fault condition.     

ABB R-MAG magnetically actuated circuit breaker.

ABB R-MAG magnetically actuated circuit breaker. Image used courtesy of  ABB

Magnetic Actuator Benefits

As a magnetically actuated breaker, the R-MAG has only one moving part, requiring little or no maintenance.

The actuator in the R-MAG is a bi-stable magnet. Two rare earth permanent magnets hold the armature closed during normal operations. A change in the state of the breaker (closed to open etc.) is initiated by electrically driven coils. When the magnetic force of a coil exceeds the force of the permanent magnets, the breaker will change state.     


Magnetic actuation of an R-MAG breaker

Magnetic actuation of an R-MAG breaker. Image used courtesy of  ABB

NEMA Enclosure Standards

Per NEMA, an electrical enclosure is a cabinet or box that protects electrical equipment and prevents shock. Each enclosure is rated to protection standards for its ability to withstand hazardous and environmental conditions.


R-MAG circuit breaker

R-MAG circuit breaker. Image used courtesy of  ABB


NEMA 1 and 2 enclosure ratings are for electrical equipment used indoors. A NEMA 3 rating is for outdoor equipment that needs to operate when exposed to windblown dust, rain, sleet, and snow. Compared with NEMA 3, a NEMA 4 rating adds protection against hose-directed water. Testing for a NEMA 4 rating includes exposing an enclosure to water at 65 gallons per minute from a 1-inch hose.