Quick Answer: ANSI or IEC — Which Standard Do You Need?
Choose ANSI C37.20.2 if your project is in the United States, Canada, or Mexico, or if your client's specification explicitly requires ANSI standards. Choose IEC 62271-200 for projects in Europe, Middle East, Asia, Africa, or Latin America (except Mexico), or when the specification calls for IEC. Both standards govern metal-clad medium voltage switchgear and set equivalent safety levels — the differences are in voltage class nomenclature, compartment requirements, and test procedures, not in fundamental safety philosophy. Our factory manufactures switchgear to both standards and can provide type test certificates for either. The key is to match the standard to the project specification and the local utility interconnection requirements.
Standards Overview: What Each Document Covers
Medium voltage switchgear standards define the minimum requirements for design, construction, type testing, routine testing, and maintenance of equipment used to switch, protect, and isolate electrical circuits in the 1–52 kV range. The two dominant standards families worldwide are:
- ANSI/IEEE C37 series (American National Standards Institute / Institute of Electrical and Electronics Engineers) — used in North America. Key documents: C37.20.2 (metal-clad switchgear), C37.20.3 (metal-enclosed switchgear), C37.20.7 (internal arc testing).
- IEC 62271 series (International Electrotechnical Commission) — used internationally. Key documents: IEC 62271-100 (AC circuit breakers), IEC 62271-200 (metal-enclosed switchgear), IEC 62271-202 (HV/LV prefabricated substations).
Both sets of standards are technically rigorous and produce equipment with equivalent safety levels. The differences that matter in practice are voltage class nomenclature, bus bar compartmentalization requirements, and short-circuit test methodology.
Voltage Ratings: Where the Standards Diverge Most Visibly
The most immediately confusing difference between ANSI and IEC switchgear is how they label voltage classes. Engineers familiar with one system are often surprised when they first encounter the other.
| ANSI System Voltage | ANSI BIL | IEC Rated Voltage (≥) | IEC BIL (Impulse) | Typical Application |
|---|---|---|---|---|
| 4.16 kV | 60 kV | 7.2 kV | 60 kV | Industrial plants, manufacturing |
| 13.8 kV | 95 kV | 12 kV | 75/95 kV | Primary distribution, utility substations |
| 26.4 kV | 125 kV | 24 kV | 125 kV | Sub-transmission, large substations |
| 34.5 kV | 150 kV | 36 kV | 170 kV | Sub-transmission, mining, wind farms |
ANSI voltage ratings are maximum continuous operating voltages. IEC ratings are maximum system voltages. Both define the minimum insulation level via BIL (Basic Impulse Insulation Level).
The most important takeaway: 13.8 kV ANSI and 12 kV IEC are not the same voltage class, but their BIL levels overlap. A 12 kV IEC switchgear with 75 kV BIL is technically insufficient for a 13.8 kV US system if the utility requires 95 kV BIL. However, a 12 kV IEC product with 95 kV BIL (the higher IEC option) is acceptable for 13.8 kV US systems — and this is what most IEC manufacturers offer for export to North America.
Compartment Requirements: The Key Structural Difference
ANSI C37.20.2 defines metal-clad switchgear with very specific compartmentalization requirements:
- The main switching device must be draw-out (removable without de-energizing the bus)
- A grounded metal barrier must separate the main bus from the cable compartment
- A grounded metal barrier must separate the circuit breaker cell from all live bus bars when the breaker is in the disconnected position
- Phase-to-phase barriers must be present in the bus compartment
IEC 62271-200 uses a different classification system based on Loss of Service Continuity (LSC) categories and accessibility classes:
| IEC 62271-200 Classification | Compartment Type | LSC Category | Arc Accessibility |
|---|---|---|---|
| Compartmentalized, interlocked breaker cell | PM (partitioned metal) | LSC 2B | Class B (front+rear) |
| Bus accessible only with full shutdown | PI (partitioned insulating) | LSC 1 | Class A (front only) |
| Fully partitioned, draw-out breaker | PM (draw-out) | LSC 2B | Class B or C |
NAIJI Electric's IEC 62271-200 switchgear is built to LSC 2B classification with PM compartmentalization — functionally equivalent to ANSI metal-clad in terms of operator safety and service continuity. This means bus bar work on one panel can be performed while adjacent panels remain energized.
Type Test Requirements Comparison
Both standards require type tests (performed once on a design prototype to qualify the design) and routine tests (performed on every unit before shipment). The type test sequence is where the standards differ most significantly from a manufacturing perspective.
| Test | ANSI C37.20.2 Requirement | IEC 62271-200 Requirement |
|---|---|---|
| Dielectric (power frequency) | 60 seconds at 2U+1 kV (AC) | 60 seconds at rated withstand voltage |
| Impulse (BIL) | 15 impulses per pole, 1.2/50 μs | 15 impulses, 1.2/50 μs per IEC 60060-1 |
| Short-circuit making & breaking | 3-operation CO-CO-CO sequence | 2-operation CO sequence |
| Short-time current (1 sec) | Rated symmetrical kA | Rated short-time withstand current |
| Temperature rise | Rated continuous current, 30°C ambient | Rated current, 40°C ambient, IEC 62271-1 |
| Internal arc (optional→required) | IEEE C37.20.7 (increasingly specified) | IEC 62271-200 Annex A (optional but standard practice) |
| Corrosion protection | Salt-spray not required by standard | IP-coded per IEC 62271-1, Cl. 4.3 |
How to Specify the Correct Standard
When writing a specification for medium voltage switchgear, the standard selection should follow this decision tree:
- Check the project location: US/Canada → start with ANSI. International → start with IEC.
- Check the utility interconnection agreement: Most US utilities specify ANSI standards in their interconnection technical requirements. This overrides any engineering preference for IEC.
- Check the owner's standard: Large industrial owners and international developers often have company standards that specify one family or the other for consistency across their facilities.
- Check the insurance/warranty requirements: Some property insurers and extended warranty providers specify equipment tested to particular standards.
- For international projects: IEC 62271-200 with third-party type test certificates from accredited laboratories (KEMA, CESI, PEHLA) is accepted worldwide. Specify "Type tested to IEC 62271-200, with test report from accredited third-party laboratory."
NAIJI Electric manufactures switchgear with type test reports covering both ANSI C37.20.2 and IEC 62271-200, enabling specification on both US domestic and international export projects. Our application engineers can review your project specification and confirm which test certificates are required — contact us with your project details.