You’re halfway through the panel spec when the supplier’s email arrives: “Can you clarify—are you requesting GFCI protection per NEC or RCD protection per IEC 61009?”
You stare at the screen. Aren’t they the same thing?
They are. Sort of. The device does the same job—but the terminology, the standards numbering, the rating nomenclature, and even the test parameters are different. Your US-trained brain says “GFCI.” The international supplier’s datasheet says “RCBO.” The panel builder in Mexico needs both terms because they serve clients in Texas and clients in Europe. One device. Two languages. And if you mix them up on a spec sheet, you’re looking at either wrong equipment, confused quotes, or a three-week delay while everyone clarifies what you actually meant.
This guide is your decoder ring. We’ll map the key correspondences between NEC (National Electrical Code, dominant in the US) and IEC (International Electrotechnical Commission, used nearly everywhere else) so you can spec, source, and install equipment across markets without translation errors.
Why This Terminology Correspondence Matters
This isn’t academic hairsplitting. When you work across borders—sourcing equipment from international manufacturers, designing panels for multinational facilities, or consulting on projects that span US and non-US installations—the terminology mismatch creates real costs.
Specification errors: You write “GFCI” on a spec sheet sent to a European supplier. They quote an RCCB (residual-current circuit breaker without overcurrent protection) because that’s the closest match in their catalog. You needed an RCBO (with integrated overcurrent protection). The panel arrives, and the protection scheme is incomplete. Re-order, re-ship, delay.
Sourcing confusion: Your procurement team finds a great price on “IP65 enclosures” from an Asian supplier. Your NEC-based project specs called for NEMA 4X (corrosion-resistant, hosedown protection). Are they equivalent? Not quite. NEMA 4X includes additional corrosion resistance tests and hosedown requirements that IP65 doesn’t cover. You install them, and six months later the coastal salt spray has corroded the enclosure gaskets. One rating system doesn’t translate directly to the other.
Standards compliance gaps: A contractor installs IEC 60947-2 MCCB รถมอเตอร์ไซค์ in a US facility, assuming “circuit breaker” means the same thing everywhere. The AHJ (authority having jurisdiction) asks for UL 489 listed breakers per NEC requirements. IEC 60947-2 breakers aren’t UL listed. The inspection fails. Rework, replace, argue about who pays.
The Decoder Ring Problem—engineers fluent in one system but illiterate in the other, leading to mis-specification, procurement delays, and field failures that could’ve been avoided with a simple terminology translation. That’s what this guide fixes.
Five Major Terminology Categories
The NEC-IEC divide shows up in five big areas. Each has its own correspondence rules and common traps:
- อุปกรณ์ป้องกันวงจรไฟฟ้า (GFCI vs RCD, AFCI vs AFDD, breaker families)
- Electrical ratings (voltage, current, breaking capacity nomenclature)
- Enclosure protection ratings (เนม่า Types vs IP Codes)
- Grounding vs earthing language (EGC vs PE conductor)
- Standards numbering systems (NEC articles vs IEC standard series)
We’ll tackle each with correspondence tables and practical decoding rules.
Category 1: Circuit Protection Devices
Here’s where the most confusion happens. The US uses umbrella terms like “GFCI” and “circuit breaker” that map to multiple distinct IEC device families, each with its own standard and scope.
| NEC/US Term | IEC Equivalent Term | มาตรฐาน IEC | Key Differences & Notes |
|---|---|---|---|
| GFCI (Ground Fault Circuit Interrupter) | RCD family | IEC 61008 (RCCB), IEC 61009 (RCBO) | RCCB = residual-current circuit breaker without integral overcurrent protection (shock protection only). RCBO = residual-current breaker with integrated overcurrent protection. US “GFCI breaker” ≈ IEC RCBO. |
| AFCI (Arc Fault Circuit Interrupter) | AFDD (Arc Fault Detection Device) | IEC 62606 | Both detect dangerous arcing faults in wiring. IEC uses “detection device” language; function is equivalent. Required in bedrooms/living areas (US NEC) and similar spaces (IEC for household installations). |
| เบรกเกอร์ (general) | MCB หรือ MCCB/ACB | IEC 60898-1 (MCB), IEC 60947-2 (industrial) | MCB (Miniature Circuit Breaker) per IEC 60898-1 for household/final circuits, max 125A, installed by ordinary persons. MCCB/ACB per IEC 60947-2 for industrial/distribution, higher ratings, installed by skilled persons only. |
| เบรกเกอร์วงจรแบบกล่องแม่พิมพ์ (MCCB) | MCCB | มอก. 60947-2 | Same term, but IEC 60947-2 scope is broader (includes ACBs). US MCCB per UL 489. Always verify UL listing for NEC installations; IEC compliance alone isn’t sufficient. |
| เบรกเกอร์หลัก | Origin of Installation CB | IEC 60364 (installation), IEC 60947-2 | IEC calls it the breaker at the “origin of installation.” Function is the same—main disconnect and overcurrent protection for the entire panel or sub-panel. |
| Branch Circuit Breaker | Final Circuit Breaker | IEC 60898-1, IEC 60364 | US “branch circuit” = IEC “final circuit.” Breakers protecting individual loads or outlet circuits. Terminology swap, same function. |
มืออาชีพ-บ#1: When sourcing protection devices internationally, specify both the function (“residual-current protection with overcurrent”) and the IEC term (“RCBO per IEC 61009”). Don’t rely on “GFCI” alone—suppliers will ask for clarification, and you’ll waste a week in email ping-pong.
Category 2: Electrical Ratings Nomenclature
Rating labels look similar until you try to compare them. NEC-trained eyes expect certain units and formats; IEC datasheets use different conventions. Miss the nuance and you’ll either overspec (wasting money) or underspec (field failure).
| Rating Parameter | NEC/US Convention | IEC Convention | Key Differences & Translation Notes |
|---|---|---|---|
| ทำลายคืน | AIC (Amperes Interrupting Capacity) in kA | Icn (rated short-circuit breaking capacity) in kA or Icu (ultimate breaking capacity) | US datasheets: “10,000 AIC” or “10 kA AIC.” IEC datasheets: Icn or Icu in kA. For MCBs (IEC 60898-1), capacity shown in amperes inside a rectangle (e.g., 6000 means 6,000A = 6 kA). For industrial CBs (IEC 60947-2), marked in kA directly. |
| Voltage ระดับความชื่นชอบ | 120V, 240V, 480V (common US levels) | 230V, 400V (common EU levels); ratings up to 1000V AC per IEC 60947-2 | US uses 120/240V split-phase residential, 480V industrial. IEC uses 230/400V three-phase. Device voltage rating must exceed system voltage; check both nominal and maximum (Ue vs Uimp). |
| ปัจจุบันระดับความชื่นชอบ | Amperes (A), marked on breaker handle or label | Amperes (A), marked on breaker; RCBOs/RCCBs rated ≤125A per latest standards | Same unit, but watch for thermal vs instantaneous trip settings on adjustable breakers. US breakers: continuous rating. IEC MCCBs: In (rated current) and adjustable thermal trip if applicable. |
| ความถี่ที่กำหนด | 60 Hz (US standard) | 50 Hz or 50/60 Hz (IEC devices often dual-rated) | Most modern IEC devices are rated 50/60 Hz, so cross-compatibility is common. Older devices may be 50 Hz only; verify before specifying for US 60 Hz systems. |
| Residual Current (RCD) | Trip current in mA (e.g., 5 mA, 30 mA) | IΔn (rated residual operating current) in mA | Same parameter, different symbol. 30 mA is the common threshold for shock protection in both systems. IEC uses IΔn; US datasheets say “trip current” or “sensitivity.” |
มืออาชีพ-บ#2: When comparing breaking capacities, watch for the IEC MCB marking trap: “6000” in a rectangle means 6,000 amperes (6 kA), not 6 A. Industrial breakers (IEC 60947-2) are marked in kA directly. Confusing the two leads to massive under-specification and catastrophic short-circuit failures.
Category 3: Enclosure Protection Ratings (NEMA vs IP)
This is the correspondence everyone wants and nobody should trust blindly. NEMA 250 enclosure Types and IEC 60529 IP Codes both describe environmental protection, but they test different things, use different methods, and cover different hazards. The official NEMA guidance (BI 50014–2024) is blunt: they are not directly equivalent.
| NEMA Type | Closest IP Code (Approximate) | What NEMA Type Covers | What IP Code Covers | Critical Differences |
|---|---|---|---|---|
| NEMA 1 | IP10 (very rough) | Indoor, general-purpose, protects against accidental contact | Limited protection (IP1X = ≥50mm objects) | NEMA 1 includes structural tests (rigidity, door-latch strength) that IP10 doesn’t. Not a true match. |
| NEMA 3 | IP54 | Outdoor, rain/sleet/windblown dust, not hosedown or submersion | Dust-protected, splashing water | NEMA 3 adds ice/sleet requirements and corrosion tests. IP54 only tests dust and splashing water. Close, but NEMA 3 is broader. |
| NEMA 3R | IP24 ถึง IP34 | Outdoor, rain/sleet, but allows some dust and water ingress | Varies; IP24 is minimal (splashing), IP34 slightly better | NEMA 3R is cheaper outdoor option (no dust-tight requirement). IP Code alone doesn’t guarantee outdoor UV/sleet performance. |
| NEMA 4 | IP66 | Hosedown/splashing water, dust-tight, indoor or outdoor | Dust-tight, powerful water jets | Close match for dust and water ingress. NEMA 4 adds corrosion resistance and structural tests (hinge/latch endurance). IP66 only addresses ingress. |
| เนม่า 4X | IP66 (partial) | Same as NEMA 4, plus corrosion resistance (stainless steel, coated) | Dust-tight, powerful water jets | NEMA 4X’s corrosion resistance is a separate test not covered by IP66. An IP66-rated mild steel enclosure rusts in coastal environments. NEMA 4X explicitly requires corrosion protection. |
| NEMA 12 | IP54 หรือ IP55 | Indoor, dust/dirt/lint, dripping/splashing non-corrosive liquids | Dust-protected, splashing or low-pressure jets | Close match, but NEMA 12 includes oil-resistance tests (gaskets must resist industrial oils). IP Code doesn’t test chemical resistance. |
| NEMA 13 | IP54 (rough) | Indoor, dust/lint, spraying water, oil/coolant seepage | Dust-protected, splashing water | NEMA 13 adds oil/coolant resistance tests (spray/seepage). IP54 tests only water, not oils. Not equivalent for machine-tool applications. |
Why You Can’t Just Swap Them
The NEMA 2024 brief makes this clear: NEMA Types include corrosion tests, structural integrity tests (hinge cycles, latch strength), and specific environmental hazards (ice, oil, coolant) that IP Codes don’t address. IP Codes focus narrowly on ingress of solids and liquids—they say nothing about whether the enclosure will corrode, whether the door latch survives 10,000 cycles, or whether the gasket resists hydraulic oil.
If your spec says NEMA 4X and the supplier quotes IP66, ask: “Is the enclosure material corrosion-resistant per NEMA 250 tests?” If they say “IP66 covers that,” they’re wrong. You’re about to install a mild-steel IP66 box that corrodes in six months.
มืออาชีพ-บ#3: Never substitute IP Codes for NEMA Types (or vice versa) without verifying the additional test requirements. For corrosion-prone environments (coastal, chemical plants, food processing with sanitizers), NEMA 4X explicitly requires corrosion tests that IP66 doesn’t include. Specify both if compliance with both systems is required, or choose the one that matches your jurisdiction and verify every test parameter.
Category 4: Grounding vs Earthing Terminology
The US says “grounding.” The rest of the world says “earthing.” Same concept, different vocabulary. But the conductor designations and color codes also differ, and that’s where wiring errors creep in.
| NEC/US Term | IEC Term | Color Code (US/NEC) | Color Code (IEC) | บันทึกย่อ |
|---|---|---|---|---|
| กับบริเวณ | Earthing | — | — | Conceptual term. NEC uses “grounding” for everything. IEC uses “earthing” for connection to earth and “bonding” for connection to PE system. |
| Equipment Grounding Conductor (EGC) | Protective Conductor (PE) | Green or Green/Yellow | Green/Yellow | Both terms describe the conductor that connects equipment frames/enclosures to earth for shock protection. IEC uses “PE” almost universally. |
| Grounding Electrode Conductor (GEC) | Earthing Conductor | Green or bare | Green/Yellow or bare | The conductor connecting the electrical system’s neutral/ground point to the grounding electrode (rod, plate, etc.). |
| Grounded Conductor | Neutral Conductor (N) | White or gray | Blue (single-phase), varies (3-phase) | In US split-phase systems, the grounded conductor is the neutral. IEC uses blue for neutral in single-phase, and specific codes for 3-phase. |
| ความผูกพันธ์ | Protective Bonding / Equipotential Bonding | — | — | Connecting conductive parts together to prevent voltage differences. US and IEC both use “bonding,” but IEC is more explicit in terminology. |
The functional difference is minimal—you’re still connecting metal enclosures to earth for safety. But on multinational projects, documentation must be clear: if you write “connect EGC,” an IEC-trained electrician might not immediately recognize it. Write “connect protective conductor (PE)” or “EGC/PE” for clarity.
Color code traps: US neutral is white; IEC single-phase neutral is blue. An IEC-trained electrician seeing a white conductor in a US panel might assume it’s a phase conductor (white isn’t used for phase in IEC, but it’s also not neutral). Label everything, especially in mixed-standard installations or international projects.
Category 5: Standards Numbering Systems
NEC uses articles and sections (e.g., NEC Article 430 for motors, Article 250 for grounding). IEC uses numeric standard series with dashes indicating parts and sub-parts. They don’t map one-to-one, but here’s the orientation:
| NEC Article/Section | Rough IEC Standard Equivalent | Scope |
|---|---|---|
| NEC Article 100 (Definitions) | IEC Electropedia (IEV) | Definitions. IEC’s International Electrotechnical Vocabulary is the global reference. |
| NEC Article 250 (Grounding) | IEC 60364-4-41, IEC 60364-5-54 | Earthing and protective conductor requirements for installations. |
| NEC Article 430 (Motors) | IEC 60034 (rotating machines), IEC 60947-4-1 (contactors/starters) | Motor requirements and motor control equipment. |
| NEC Article 440 (HVAC) | IEC 60335-2-40 (heat pumps, air conditioners) | HVAC-specific safety and installation rules. |
| UL 489 (Circuit Breakers) | IEC 60947-2 (industrial CBs), IEC 60898-1 (household MCBs) | US molded-case and low-voltage circuit breakers vs IEC families. |
| UL 943 (GFCI) | IEC 61008 (RCCB), IEC 61009 (RCBO) | Ground-fault / residual-current protection devices. |
| NEMA 250 (Enclosures) | IEC 60529 (IP Code) | Enclosure ingress protection. Not equivalent, as discussed above. |
The IEC numbering logic: 60947 is the low-voltage switchgear family, 60947-2 is circuit breakers within that family, 60947-4-1 is contactors and motor starters. The dashes divide topic (60947 = switchgear), part (2 = breakers), and sub-part (4-1 = contactors). NEC uses sequential article numbers without the hierarchical dash system.
When writing specs, cite both if your project spans jurisdictions: “Circuit breakers shall comply with UL 489 (for US installations) or IEC 60947-2 (for international installations), as applicable.”
Three Common Confusion Traps (And How to Avoid Them)
Even experienced engineers hit these traps when moving between NEC and IEC worlds. Here’s how to dodge them:
Trap 1: Assuming “Circuit Breaker” Means the Same Thing
ปัญหา: In the US, “circuit breaker” is a catch-all term. In IEC-land, you must distinguish between MCBs (IEC 60898-1) for household/final circuits and MCCBs/ACBs (IEC 60947-2) for industrial/distribution applications. They look similar, but they’re governed by different standards, have different voltage impulse ratings (Uimp), and are intended for different users.
IEC 60898-1 MCBs are designed for ordinary persons installing final circuits in homes and light commercial buildings—max 125A, typically lower breaking capacities (up to 25 kA Icn), and simpler coordination requirements. IEC 60947-2 industrial breakers are for skilled electricians, cover higher currents and voltages (up to 1000V AC / 1500V DC per the 2024 edition), and include more rigorous tests for isolation suitability and EMC.
Real failure case: A contractor spec’d IEC 60898-1 MCBs for the main distribution panel in a manufacturing facility because “they’re cheaper and the current rating fits.” Six months later, a three-phase fault on the production floor generated a 35 kA short-circuit current. The MCBs (rated Icn = 10 kA) failed catastrophically—contacts welded, enclosures cracked. Root cause: wrong breaker family. The spec should have called for IEC 60947-2 MCCBs with Icu ≥50 kA.
How to avoid it: Ask yourself: is this a final circuit (lighting, outlets, small loads) or a distribution/feeder circuit (main panel, sub-panel, large motor feeders)? Final circuits → IEC 60898-1 MCB. Distribution/industrial → IEC 60947-2 MCCB or ACB. When in doubt, check the available fault current and compare against the breaker’s rated breaking capacity (Icn or Icu). If fault current exceeds the breaker’s capacity, you’ve spec’d the wrong device.
Trap 2: Misreading IEC Breaking Capacity Markings
ปัญหา: IEC 60898-1 MCBs mark their short-circuit capacity in amperes inside a rectangle—for example, “6000” means 6,000 amperes, or 6 kA. IEC 60947-2 industrial breakers mark capacity directly in kA. If you’re not paying attention, you see “6000” on an MCB and think “6 kA,” which is correct—but then you see “10” on an industrial breaker and think “10 amperes,” which is catastrophically wrong. It’s 10 kA (10,000 amperes).
How to avoid it: Always check which standard the breaker is certified to (look for “IEC 60898-1” or “IEC 60947-2” on the label). If it’s 60898-1, the number in the rectangle is amperes (divide by 1000 for kA). If it’s 60947-2, the marking is already in kA. When in doubt, consult the datasheet’s Icn or Icu row—it’ll clarify the units.
Trap 3: Treating NEMA 4X and IP66 as Equivalent
We covered this above, but it’s worth repeating because it’s the #1 enclosure specification error.
ปัญหา: NEMA 4X includes corrosion resistance testing (salt spray, specific materials like stainless steel or corrosion-resistant coatings). IP66 only tests dust and water ingress. A mild-steel enclosure can be IP66-rated and still rust to pieces in a coastal or chemical environment because IP66 doesn’t test corrosion.
Real failure case: A food processing facility spec’d NEMA 4X enclosures for control panels in a washdown area with aggressive sanitizers (chlorine-based). Procurement sourced “equivalent” IP66 enclosures from an overseas supplier—painted mild steel. Within eight months, the sanitizer spray corroded through the paint, rusted the enclosure, and compromised the door gasket seal. Water ingress damaged the PLC, costing $15,000 in downtime and replacement. NEMA 4X would have required stainless steel or corrosion-resistant coating that could withstand the sanitizer.
How to avoid it: If your spec calls for NEMA 4X, verify that the enclosure material and coating meet NEMA 250’s corrosion resistance requirements—regardless of IP rating. If you’re substituting IP66 for NEMA 4X, get written confirmation from the supplier that the enclosure has been tested for corrosion per ASTM B117 or equivalent salt-spray tests. Better yet: specify both ratings if your project requires both NEC and IEC compliance. “Enclosures shall be NEMA 4X per NEMA 250 แล้ว IP66 per IEC 60529, with stainless steel construction or corrosion-resistant coating verified by salt-spray testing per ASTM B117.”
มืออาชีพ-บ#4: The three traps above account for roughly 70% of cross-system specification errors. Memorize them, or print this section and tape it to your monitor. Every time you write “circuit breaker,” “breaking capacity,” or “enclosure rating” on a spec that might cross NEC-IEC boundaries, double-check which system you’re in and whether the terminology is actually equivalent.
Your Cross-System Specification Checklist
You’re not going to memorize every correspondence in this guide. That’s fine. What you need is a checklist to catch translation errors before they become purchase orders.
Before you finalize any spec, RFQ, or equipment list that might span NEC and IEC systems, run through this:
- ☐ Protection devices: Did I specify the function (“residual-current protection with overcurrent”) in addition to the term (“GFCI” or “RCBO”)? If I wrote “GFCI,” did I clarify whether I need an RCCB (no overcurrent) or RCBO (with overcurrent)?
- ☐ เบรกเกอร์: Did I distinguish between final-circuit breakers (IEC 60898-1 MCB) and industrial/distribution breakers (IEC 60947-2 MCCB/ACB)? Did I verify the breaking capacity in the correct units (kA vs amperes in a rectangle)?
- ☐ Enclosures: Did I specify environmental protection using ทั้งคู่ NEMA Type and IP Code if the project spans jurisdictions? If I substituted one for the other, did I verify corrosion resistance, structural tests, and environmental hazards (ice, oil, coolant) that one system covers and the other doesn’t?
- ☐ Grounding/Earthing: Did I use both terms (“EGC/PE” or “grounding/earthing”) in documentation for multinational teams? Did I specify conductor color codes explicitly to avoid cross-system wiring errors?
- ☐ Standards citations: Did I cite both NEC articles and IEC standards where applicable (“per NEC Article 430 and IEC 60947-4-1, as applicable to jurisdiction”)? Did I verify that IEC-compliant devices have the required UL/CSA listings for US installations?
- ☐ Voltage and frequency: Did I confirm that IEC devices rated for 50 Hz will work on 60 Hz systems (most modern devices are dual-rated 50/60 Hz, but older devices may not be)? Did I verify voltage compatibility (120V vs 230V, 240V vs 400V)?
Run through that checklist before you hit “send” on the RFQ or “approve” on the purchase order. Catch one NEMA 4X vs IP66 error, and you’ve just saved $15,000 and a three-week delay. Catch a breaking-capacity misread, and you’ve prevented a catastrophic fault that could’ve injured someone.
มาตรฐา&แหล่งข่าวของลองโยง
- IEC 60947-2:2024 (Low-voltage switchgear and controlgear – Part 2: Circuit-breakers, Ed. 6.0, published 2024-09-18)
- IEC 61009-1:2024 (Residual-current circuit-breakers with integral overcurrent protection – RCBOs, Ed. 4.0, published 2024-11-21)
- IEC 61008-2-1:2024 (Residual-current circuit-breakers without integral overcurrent protection – RCCBs, Ed. 2.0, published 2024-11-21)
- IEC 62606 (General requirements for arc fault detection devices, consolidated version through 2022)
- IEC 60898-1 (Circuit-breakers for overcurrent protection of household and similar installations – MCBs)
- IEC 60529 (Degrees of protection provided by enclosures – IP Code)
- NEMA 250-2020 (Enclosures for Electrical Equipment, 1000 Volts Maximum)
- NEMA BI 50014–2024 (A Brief Comparison of NEMA 250 and IEC 60529)
- NEC 2023 (NFPA 70, National Electrical Code)
- UL 489 (Molded-Case Circuit Breakers, Molded-Case Switches, and Circuit-Breaker Enclosures)
- UL 943 (Ground-Fault Circuit Interrupters)
- IEC Electropedia (IEV 826-13-22, Protective Conductor definition)
Timeliness Statement
All standards versions, technical specifications, and correspondence guidance accurate as of November 2025.
