Interpretation of Symbols on Circuit Breakers
According to national technical standards, the models of circuit breakers are typically composed of numbers and letters. Different types of circuit breakers are identified by specific letters, with the symbols representing various characteristics. Below is a breakdown of these symbols:
1. First Letter in the Circuit Breaker Model
The first letter in the circuit breaker model indicates the type of circuit breaker:
- S – Less oil circuit breaker
- D – More oil circuit breaker
- K – Air circuit breaker
- Q – Gas circuit breaker
- C – Magnetic blowout circuit breaker
- Z – Vacuum circuit breaker
- L – Sulfur hexafluoride (SF6) circuit breaker
2. Second Letter: Installation Environment
The second letter represents the installation environment:
- N – Indoor installation
- W – Outdoor installation
3. Numbers and Additional Symbols
- The third digit represents the company’s design sequence number.
- The fourth digit indicates the rated voltage (in kV).
- The fifth letter represents the function type, such as:
- G – Improved type
- F – Split-phase operation
- The sixth digit represents the rated current (in amperes).
- The seventh digit indicates the rated breaking current (in kA).
- The eighth digit represents the special environmental code of the circuit breaker.
Types of Circuit Breakers
- Low-voltage circuit breakers: Miniature circuit breakers, molded case circuit breakers, earth leakage circuit breakers, universal circuit breakers, frame circuit breakers, motor circuit breakers, etc.
- High-voltage circuit breakers: High-voltage SF6 circuit breakers, high-voltage vacuum circuit breakers, outdoor and indoor high-voltage vacuum circuit breakers.
Symbol Representation in Electrical Diagrams
- QF – Circuit breaker
- QS – Molded case circuit breaker (protection switch)
The static contact of QF can operate under load, while QS’s static contact cannot operate with load. “Q” refers to the power circuit switchgear, and “F” refers to the protection device. The letter “S” distinguishes a circuit breaker from an isolation switch. Circuit breakers are designed to close, carry, and break current under normal and abnormal circuit conditions.
Example: Circuit Breaker Model NM1-100S/3300
- N – Company code
- M – Molded case circuit breaker
- 1 – Design serial number
- 100 – Rated current
- S – Segment capability feature (S: standard type, H: higher type, R: current-limiting type)
- 3300 – Represents a 3-pole switch (4 would represent a 4-pole switch).
The second digit indicates the type of release:
- 3 – Thermal magnetic release
- 2 – Electromagnetic release
- 1 – No trip
The third and fourth digits represent attachments:
- 00 – No attachments
- 08 – Alarm contact
- 10 – Shunt release
- 20 – Auxiliary contact
- 30 – Undervoltage release
- 40 – Shunt release and auxiliary contact
- 50 – Shunt release and undervoltage release
- 60 – Two sets of auxiliary contacts
- 70 – Auxiliary contacts and undervoltage release
- 18 – Shunt release and alarm contact
- 28 – Auxiliary contacts and alarm contact
- 38 – Undervoltage release and alarm contact
- 48 – Undervoltage release, auxiliary contacts, and alarm contact
- 58 – Shunt release, undervoltage release, and alarm contact
- 68 – Two sets of auxiliary contacts and alarm contact
- 78 – Auxiliary contact, alarm contact, and undervoltage release
Technical Specifications
- Ui – Rated insulation voltage
- Ue – Rated working voltage
- Uimp – Rated impulse withstand voltage
- Ii – Ten times the rated current (Ii = 10 In)
- 50Hz – Frequency
- Icu – Rated ultimate short-circuit breaking capacity
- Ics – Rated operating short-circuit breaking capacity