IEC 62271-103 classifies the general-purpose switch by electrical endurance as E1 (basic), E2 (extended) and E3 (high). The class is chosen according to operating frequency and whether inspecting and replacing switching parts is acceptable. Mechanical and capacitive endurance are designated separately.
Short answer
IEC 62271-103 (edition 1.0, 2011) covers switches for rated voltages above 1 kV up to 52 kV. A general-purpose switch can perform all the making and breaking operations that normally occur in a distribution network, with currents up to its rated breaking currents. It can also carry and make short-circuit currents (clause 3.4.103).
Within that general purpose, classes E1, E2 and E3 measure how many operations with current the equipment withstands: basic, extended and high electrical endurance.
What the standard covers
IEC 62271-103 applies to three-phase AC switches and switch-disconnectors in their switching function. It covers equipment with making and breaking capability, for indoor or outdoor installation. Its scope is above 1 kV up to 52 kV and from 16 2/3 Hz to 60 Hz (clause 1.1). It also applies to single-pole switches used in three-phase systems, their operating mechanisms and their auxiliary equipment.
A switch-disconnector is a switch that, in the open position, meets the isolating requirements of a disconnector (clause 3.4.102).
The three electrical classes
| Class | Electrical endurance | When the standard considers it suitable |
|---|---|---|
| E1 | Basic | Infrequent operation, or where inspecting and replacing the switching parts is allowed |
| E2 | Extended | Infrequent operation, but with no possibility or permission to inspect and replace parts |
| E3 | High | Frequent operation, with no possibility or permission to inspect and replace parts |
Electrical endurance refers to breaking load currents and making on short circuit (clauses 3.4.103.1 to 3.4.103.3). The standard presents these descriptions as application notes, not as mandatory rules.
The mechanical and capacitive classes
The electrical class is not the only one designated. Besides E, a switch carries its mechanical class and, where applicable, its capacitive class (clause 4.116):
- M1: mechanical endurance of 1,000 operations.
- M2: special service and frequent operation, with extended mechanical endurance of 5,000 operations.
- C1: capacitive current breaking capability demonstrated with specific tests.
- C2: very low probability of restrike when breaking capacitive current, demonstrated with the same specific tests.
Each switch is first designated by its type: general purpose, limited purpose or special purpose. According to clause 4.116, the electrical class E1, E2 or E3 is designated for the general-purpose switch.
Which currents a general-purpose switch must handle
Clause 4.112 sets the capabilities of a general-purpose switch. Each rated breaking current is expressed with its own value:
- Mainly active load current, equal to the rated normal current.
- Distribution line closed-loop breaking current, also equal to the rated normal current.
- Cable-charging current and line-charging current, with the preferred values of Table 1 of the standard.
- Short-circuit making current, equal to the rated peak withstand current.
- If used in networks with non-effectively earthed neutral: earth-fault breaking current and cable- and line-charging current under earth-fault conditions.
The standard values are taken from the R10 series (1 – 1.25 – 1.6 – 2 – 2.5 – 3.15 – 4 – 5 – 6.3 – 8 and their multiples of ten).
Which classes the standard mentions for each type
When choosing the class, clause 8.104 refers to the definitions of clause 3.4 and distinguishes by switch type:
| Type | Classes to which clause 8.104 refers |
|---|---|
| General purpose | E1, E2, E3, M1, M2, C1 and C2 |
| Limited purpose | M1, M2, C1 and C2 |
| Special purpose | Its capabilities and classes are defined in clause 3.4.105 |
How to choose the class
- Is inspecting and replacing switching parts allowed?
- Yes: E1
- No: Will it operate frequently?
- Yes: E3
- No: E2
The mechanical class is chosen separately: M1 corresponds to 1,000 operations and M2 to special service and frequent operation, with 5,000.
Conditions worth telling the manufacturer
Clause 8.102 asks to inform the manufacturer of unusual service conditions. Some weigh directly on the class selected:
- Unusual operation, with a high switching frequency or difficult maintenance.
- Pollution, abrasive dust, excessive humidity or salt fog.
- Abnormal vibration, shock, tilting or seismic activity.
- Very high or very low ambient temperatures, and high altitude.
- A frequency different from the rated one, such as the harmonics associated with capacitor banks or rectifiers. In that case, the rated current must withstand the power-frequency current and the harmonic currents.
What information to include when ordering
Clause 9.1 of the standard lists what the person inquiring about or ordering a switch must state:
- The type and class, according to the definitions of clause 3.
- Whether it is for indoor or outdoor installation.
- The rated voltage, the insulation level and the rated frequency.
- The rated normal current, the breaking currents and the short-circuit making current.
- The short-circuit duration, if different from the standard one.
- The type tests requested specially.
- The type of operating mechanism, manual or motorized, and spare auxiliary contacts.
- System conditions that affect the equipment: harmonics, resonances and the expected number of operations.
What not to do
- Do not order “a switch” without stating type and classes: the standard requires designating them.
- Do not assume E3 includes M2. Each class is designated separately.
- Do not use it to break short-circuit currents: its rated breaking currents are those of the list in clause 4.112.
- Do not choose E1 for an application where parts cannot be inspected or replaced.
Related topics
The switch is introduced as equipment in the guide on the medium-voltage switch-disconnector. Medium-voltage switchgear and its interlocking are explained separately. To break short circuits there is the medium-voltage vacuum circuit breaker. For the condition of its switching parts, see medium-voltage switchgear maintenance.
The breaking and making currents that accompany each class are detailed in rated currents of a switch. For capacitor banks and motors there is the special type: special-purpose switch.
The map of standards for primary equipment testing places this part among the others of IEC 62271.
When to call us
At Tiza Group we review with you the electrical, mechanical and capacitive class your network’s switches need, and we verify them at commissioning. See our testing and commissioning service, available in Colombia or elsewhere on request. Write to us and we will send you a quote.
Related guides
- Rated currents of a switch
- Special-purpose switch
- Medium-voltage switch-disconnector and RMU and their tests
- Medium-voltage switchgear: parts, functions and tests
- Medium-voltage vacuum circuit breaker: function and tests
References
- IEC 62271-103, High-voltage switchgear and controlgear - Part 103: Switches for rated voltages above 1 kV up to and including 52 kV, 2011 edition: clauses 1.1, 3.4.102 to 3.4.105, 4.112, 4.116, 8.102, 8.104 and 9.1.
Frequently asked questions
What is the difference between classes E1, E2 and E3?
It is the electrical endurance of the switch when breaking load currents and making on short circuit: basic in E1, extended in E2 and high in E3. E1 suits infrequent operation where inspecting and replacing parts is allowed. E2 suits infrequent operation where inspection is not possible. E3 suits frequent operation where inspection is not possible.
Does class E3 include mechanical class M2?
No. The standard designates each characteristic separately: mechanical endurance with M1 or M2, electrical with E1, E2 or E3, and capacitive with C1 or C2. When ordering the equipment, each class must be stated.
Does a load-break switch break short circuits?
That is not its function. Its rated breaking currents are active load, closed-loop, cable-charging and line-charging, and earth-fault currents. It must, however, carry the short-circuit current and make on it.