Switch Interrupter Attachments

Guide to Disconnect Switch Mounted Interrupters

Full load break interrupter attachments offer the most operating flexibility and efficiency as they can be switched under most system conditions.

As system loads have grown and the demand for reliability (reduced outage duration) has increased, it has become necessary to operate transmission and sub-transmission systems in a manner similar to distribution systems where outages are limited to smaller sections of the system. This has led to an increased usage of switch mounted attachments which add loop splitting, line dropping, and load dropping capabilities, depending upon the device selected.

Full load break interrupter attachments offer the most operating flexibility and efficiency as they can be switched under all normal system conditions. This eliminates any concerns of a system operator making an error in switching sequence that could result in an unintended system outage.

Available disconnect switch mounted interrupting devices include:

The LLS® family of single gap SF6 full load break interrupter attachments offers the most flexibility when switching transmission, sub-transmission or distribution lines as it is the most capable interrupter available in the market with full load break interrupting ratings (3000 Amperes), line dropping ratings (300 Amps), and loop splitting ratings up to 3000 Amps.

38kV - 242kV

Line dropping up to 300 Amps

Loop splitting up to 3000 Amps

Load switching up to 3000 Amps



Single Bottle Vacuum attachments add the capability of loop splitting on systems to 230 kV where the voltage drop across the open gap of the switch does not exceed 30 kV. It has no load break capability above 34.5 kV.

Loop splitting < 2000 Amps


High Speed Whip (HSW) A high speed whip type air switch attachment used to interrupt transformer magnetizing and line charging current.  Can be applied on vertical break and side break switches in both standard and slant style configurations.

Charging Current up to 20 Amps


Whip type arcing horns increase the line dropping capability of a disconnect by increasing the speed of contact separation during the opening of a switch. It is difficult to specify the exact level of interrupting capability as factors such as phase spacing, wind, rain, humidity, and atmospheric pollution will affect the arc that is drawn as the whip contact separates from the jaw of the switch. Over time the capability of the whip type arcing horn is affected due to the change in length of the whip resulting from the arcing that occurs during interruption.

Line Charging < 12 Amps


Standard arcing horns have no loop splitting or load break capability and very limited line dropping capability. They are often utilized on switches to minimize the wear of the main contacts.

Line charging < 2 Amps






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