| Publisher | IEEE |
|---|---|
| Type | Standard (family of standards and guides) |
| Scope | Ratings, testing and application of switchgear, circuit breakers, fuses, protective relays and related equipment, together with guides for power system protection. |
| Who uses it | Protection engineers, switchgear designers and manufacturers, utility and industrial power engineers, testing and commissioning teams. |
| Edition note | The C37 family includes many individual documents, each with its own edition. Refer to IEEE for the current edition of each document. |
What It Is
The C37 series is a large collection of standards, recommended practices and guides covering switching and protection equipment in North American power systems. Many documents carry joint ANSI and IEEE designations, reflecting their long history as American National Standards. The family covers the equipment itself, such as high-voltage circuit breakers, low-voltage power circuit breakers, metal-enclosed switchgear and relays, as well as application guides for protecting lines, transformers, generators, motors and buses.
Some C37 documents are used daily by nearly every protection engineer. IEEE C37.2 defines the standard electrical power system device function numbers, such as 50 and 51 for overcurrent, 87 for differential and 21 for distance protection. IEEE C37.90 sets requirements for relays and relay systems. IEEE C37.111 defines COMTRADE, the common format for transient data exchange, and IEEE C37.118 addresses synchrophasor measurements. The C37.20 subseries covers metal-enclosed switchgear, and C37.110 is a guide for applying current transformers for protection.
Why It Matters
North American utility and industrial systems are specified, purchased and tested to C37 documents. Equipment ratings drawn from these standards, such as interrupting capability and short-time withstand, determine whether switchgear can safely handle available fault current, a key input to arc flash and short-circuit studies.
The application guides capture decades of industry experience on how to protect equipment reliably and selectively. Using them helps engineers avoid both nuisance tripping and failures to trip, and creates a shared vocabulary between utilities, manufacturers and consultants. For engineers moving between North American and international projects, knowing which C37 document corresponds to which IEC standard is a practical skill. Ratings, test philosophies and terminology differ in places, and specifications that mix the two families without care can leave gaps in equipment capability or acceptance testing.
Key Concepts
- Device function numbers — IEEE C37.2 numbers and suffixes that identify protective and control functions on drawings and in relay settings.
- Equipment ratings — rated voltage, continuous current, interrupting current and short-time withstand that define what switchgear can safely do.
- Relay performance requirements — requirements for relay operation under defined environmental, electrical and surge conditions.
- COMTRADE — a common file format for fault records and test data that allows exchange between relays, recorders and analysis tools.
- Synchrophasors — time-synchronized phasor measurements used for wide-area monitoring and control.
- Protection application guides — recommended practices for protecting specific power system elements, including setting philosophy and coordination.
- Instrument transformer application — guidance on selecting current and voltage transformers so protection performs correctly during faults.
- Metal-enclosed switchgear — the C37.20 subseries defines types, ratings and tests for metal-clad and other metal-enclosed switchgear assemblies.
Who Should Know It
- Protection and control engineers
- Switchgear and relay design engineers
- Utility planning and operations engineers
- Commissioning and relay test technicians
- Industrial power system engineers
Related Standards
- IEC 60255 — the international relay standard; some documents, such as COMTRADE and synchrophasor standards, are dual-logo IEC/IEEE publications.
- IEC 62271 — the international counterpart for high-voltage switchgear and controlgear.
- IEEE 1584 — arc flash calculations depend on C37 equipment ratings and protective device clearing times.
- IEC 61850 — the communication standard used in modern protection and control systems.
How ASEEE Uses It
ASEEE protection programs map learning outcomes and assessments to the C37 family, especially device function numbering, equipment ratings and protection application practice. See related ASEEE programs.
ASEEE Programs Referencing This Standard
- Advanced Power System Analysis with ETAP
- Low-Voltage and High-Voltage Engineering
- Modern Power System Protective Relaying
- Power System Protection and Relay Testing
- Safe Isolation for Low and High Voltage Systems
- Substation Design: Main Equipment
Educational summary only. ASEEE is not the publisher of this document and this page does not reproduce or replace it. Always consult the current official edition from IEEE for requirements.