Omnipresent interrupters

Interrupters, small and large, can be found everywhere from homes to all industries

By Claire Marchand

Interrupters are used for a wide range of applications and in switching devices from circuit breakers to switches and reclosers. They are essential to the protection of equipment such as transformers and, in the case of residual-current devices, for saving lives and protecting equipment by interrupting the electrical flow. Several IEC TCs (Technical Committees) and SCs (Subcommittees) prepare International Standards for various types of interrupters and for the devices that use them.

AEG air circuit breaker for low voltage power distribution switchgear AEG air circuit breaker for low voltage power distribution switchgear

From small to…

Interrupters disconnect a circuit whenever they detect a fault condition, such as an overload or a short circuit.

Interrupters are used in many applications; the most common, with which most people are familiar, is the RCD (residual-current device) also known as RCCB (residual-current circuit breaker). These devices have replaced fuses in many households. RCDs are safety devices that automatically disconnect the AC (current) power supply if an imbalance is detected between the live and neutral components of the current supply. This enables them to protect individuals and equipment by preventing electrocution or damage to appliances or other equipment. Unlike fuses that must be replaced after current is cut off, circuit breakers can be reset to resume operation after tripping.

One application of RCDs that is set to gain importance is their inclusion in charging installations for EVs (electric vehicles). IEC SC 23E: Circuit-breakers and similar equipment for household use, prepares International Standards for such devices, as well as for RCDs in other equipment.

Other types of interrupters are AFCIs (arc fault circuit interrupters) which are responsible for cutting arcing-faults in electrical circuits that could cause fires. AFCIs reduce the risk of fire beyond the scope of conventional fuses and circuit breakers.


While they are used in a range of switching devices such as large circuit breakers, interrupters are also ubiquitous in all industrial domains from power generation and distribution to transport and manufacturing. They ensure safe and reliable operation by protecting installations.

Interrupters play a major role in safeguarding power generation and distribution. They are used to protect distribution transformers from overloads and secondary faults and to switch them “on” or “off”. They can also be found in reclosers: circuit-breakers used on overhead distribution systems to detect and interrupt momentary faults and then to restore power automatically to the lines once faults are cleared.

Reclosers use oil, vacuum, or SF6 (sulphur hexafluoride) gas interrupters. SC 17A prepares International Standards for "automatic reclosers and fault interrupters for alternating current systems up to 38 kV".

Safety though vacuum

Power network operators rely overwhelmingly on vacuum interrupters for their switching devices. Vacuum interrupters are special switches made of one fixed contact and one mobile contact. Both are enclosed in a tight and highly evacuated vacuum ceramic chamber. Vacuum is the ideal choice as it has much higher dielectric strength (insulating property) than air.

The over-riding advantage of vacuum interrupters is that their properties remain constant throughout their entire life cycle, due to the hermetically sealed vacuum interrupter by means of which any external influence is eliminated. They also recover quicker than other types of interrupters in case of voltage surges: vacuum allows them to cool quicker than gas- or air-filled interrupters.

About 80% of power network operators implement vacuum switching technologies. In Germany, the market share of vacuum circuit-breakers is close to 100%, according to that country’s Siemens AG.

Multiple applications, multiple and diverse standards

Interrupters, which are essential to many a range of applications in the domestic and industrial environments, are included in countless devices and systems. As a result, International Standards for the various kinds of interrupters and equipment that use them are prepared by several IEC TCs.

TC 17: Switchgear and controlgear, and its SCs "prepare international standards regarding specifications for circuit-breakers, switches, contactors, (…) and any switchgear assemblies, with the exception of those for domestic and similar use", which are covered by SC 23E. 
SC 22H prepares International Standards for UPS (uninterruptible power systems). UPS are devices that protect from power spikes or provide emergency power when the power source (essentially from the mains) fails. 

UPS use interrupters and are essential to shield systems from the consequences of power cuts or surges. They protect small equipment like computers and communication gear, or larger and critical installations, such as hospitals, data or communication centres.

TC liaison and coordination ensure quality across domains

As the work of these TCs and SCs includes various interrupters and may overlap in certain domains, they maintain close liaison and coordinat continuously to ensure they prepare the best possible and most relevant International Standards.

Manufacturers of switchgear and interrupters frequently highlight the conformity of their circuit-breaker and interrupter products with IEC International Standards, such as the IEC 62271High-voltage switchgear and controlgear, series to stress their quality and reliability.

Since interrupters are present in so many devices and deployed in practically all industrial domains, work by all these IEC TCs and SCs to improve their characteristics and performance is set to continue apace.

AEG air circuit breaker for low voltage power distribution switchgear AEG air circuit breaker for low voltage power distribution switchgear
ind-1_gfci_lrg Ground fault circuit interrupters
Siemens 72.5-kV circuit-breaker with vacuum interrupter tested "in accordance with IEC 62271-100" (Photo: Siemens AG) Siemens 72.5-kV circuit-breaker with vacuum interrupter tested "in accordance with IEC 62271-100" (Photo: Siemens AG)