NOJA Power

Technical Article

Published 04/2023

Three Network Applications for Single Triple Reclosers

NOJA Power's Single Triple Recloser

Un-ganged three phase Reclosers, also known as Single Triple Reclosers are commonly applied in North American style distribution networks as a method of providing electrical protection to the four wire distribution grid. However, this is not their only application.

NOJA Power manufactures various phase configuration reclosers, including standard 3 phase ganged units, two pole single phase units and single triple devices. With over 90,000 installations in 104 countries worldwide, the OSM Recloser has addressed both the conventional single-triple application and other unique network protection scenarios.

In this article, we review an overview of the original application, along with two other niche applications which have emerged over NOJA Power’s service of this market with their OSM Recloser product.

Application One: Protecting the Four Wire Distribution Network

The North American electricity distribution network is designed for simple extensibility. Contrary to the European three wire network design, the North American network topology uses a four-wire system with a neutral.

This design allows North American networks to connect loads phase to ground, with the return path being the neutral conductor. Typically, these transformer connections are far smaller than the 3 phase distribution units seen on European networks, simplifying the process of minor network augmentations. However, this method reduces visibility of earth faults, as the network generally runs unbalanced.

Since low voltage distribution lines are connected via a phase to ground connection alone, it becomes possible to trip only a single phase of a 4 wire system when any single line becomes faulted.

In the European system, a fault would create an outage for all customers connected to the same 3 phase transformer. In the North American topology, only the faulted phase will be affected by an outage.

To achieve this, utility engineers use an un-ganged three phase recloser. These Single Triple reclosers have the ability to protect and trip individual phases, or alternatively trip all three phases to lockout. This is the most common application of the Single Triple NOJA Power OSM Recloser.

A NOJA Power OSM Recloser Single Triple Installation in the USA
A NOJA Power OSM Recloser Single Triple Installation in the USA © NOJA Power 2023

Application Two: Faulted Phase Grounding

Among experimental technologies for fire risk mitigation, faulted phase grounding is a method where a single triple OSM Recloser is connected in parallel to ground from the three phase overhead distribution line in a normally open position.

The application concept is to collapse the voltage on a faulted phase under fault conditions.

When a fault occurs downstream of the substation with the single triple faulted phase grounding system, a signal from the earth fault detection system is passed to the NOJA Power OSM Recloser. The recloser then closes the phase which is responsible for the fault, introducing a short circuit in the substation and reducing the voltage out on the feeder at the fault site.

A faulted phase grounding Single Triple OSM Recloser installation
A faulted phase grounding Single Triple OSM Recloser installation © NOJA Power 2023

Application Three: Protection of Triplex SWER

In remote parts of distribution networks around the world, some utilities elect to split a three phase overhead distribution network into three independent Single Wire Earth Return (SWER) feeders. At this point of separation, a Single Triple OSM Recloser could be applied.

Rather than 3 independent protection systems, a single NOJA Power OSM Recloser could be used to protect all three distribution feeders. This condenses three control systems into one and allows a single point of connection for SCADA control.


“Single triple reclosers make sense on a four wire distribution system to keep supply onto one or two phases only using the single-phase trip single phase lockout functionality,” says NOJA Power Group Managing Director Neil O’Sullivan.
“Equally they are not suitable for three wire networks that require all three phases to open and lockout. There are however interesting solutions where single triple reclosers can be deployed in very specific applications on 3 wire networks with some creative engineering.”

For more information about NOJA Power’s OSM Reclosers, Ground Mount Kiosk Switchgear or any other medium voltage protection products, visit

Want to stay up to date with Electrical Distribution Technology?

Join our list for a free weekly technical bulletin, as we share our Global Electrical Engineering experience directly to your inbox.