Eaton FAZ Circuit Breaker Selection Guide: B, C, D, K, S, Z Trip Curves Explained

{
“@context”: “https://schema.org”,
“@type”: “FAQPage”,
“mainEntity”: [
{
“@type”: “Question”,
“name”: “What is the difference between FAZ and FAZ-NA?”,
“acceptedAnswer”: {
“@type”: “Answer”,
“text”: “FAZ-NA is the North American catalog variant, UL 489 listed. Functionally identical to the standard FAZ (which is IEC 60898), but with different certifications and a different catalog numbering convention.”
}
},
{
“@type”: “Question”,
“name”: “Can I substitute FAZ-B for FAZ-C?”,
“acceptedAnswer”: {
“@type”: “Answer”,
“text”: “Generally no. Curve B trips at 3 to 5 × In, while curve C trips at 5 to 10 × In. If a downstream motor has high inrush, a curve B MCB will nuisance-trip. Always match the curve to the load type.”
}
},
{
“@type”: “Question”,
“name”: “What is the maximum short-circuit rating of the FAZ?”,
“acceptedAnswer”: {
“@type”: “Answer”,
“text”: “The standard FAZ is rated 10 kA or 15 kA at 400 V AC, depending on the catalog number. For higher fault currents, use the FAZ-XKH… or move up to the NZM molded case circuit breaker range.”
}
},
{
“@type”: “Question”,
“name”: “Do FAZ MCBs work with DC circuits?”,
“acceptedAnswer”: {
“@type”: “Answer”,
“text”: “Yes — the FAZ-DC family is rated for DC applications up to 250 V DC per pole. The standard FAZ is for AC only.”
}
},
{
“@type”: “Question”,
“name”: “What is the lead time for FAZ in international B2B orders?”,
“acceptedAnswer”: {
“@type”: “Answer”,
“text”: “Common FAZ SKUs (FAZ-B6/3, FAZ-C10/3, FAZ-C16/1) are usually in stock for 2 to 4 weeks lead time. Less common variants (curves K, S, Z) may take 4 to 6 weeks.”
}
}
]
}

For B2B buyers specifying final-distribution protection in industrial and commercial switchgear, the Eaton FAZ circuit breaker is one of the most common miniature circuit breakers (MCBs) in IEC 61439-compliant panels. The FAZ family (originally Moeller xEffect) covers 0.5 A to 63 A in single-pole, double-pole, triple-pole, and four-pole configurations, and supports six distinct tripping characteristics — B, C, D, K, S, and Z — each tuned for a different load profile.

This B2B guide walks through the practical selection workflow for the FAZ family: which trip curve to choose for which application, how to size the breaker for continuous and inrush loads, and how to compare the FAZ-NA and FAZ-RT variants used in international B2B projects.

1. Why the Eaton FAZ MCB Is a B2B Industry Default

The Eaton Moeller xEffect FAZ is the de facto MCB for final distribution in European-style switchgear. Three reasons it remains the B2B default:

Universal certification — IEC 60898 (residential and light commercial) and UL 489 (North American industrial), in the same catalog number family.
Six trip curves — B, C, D, K, S, and Z, allowing a single MCB family to cover residential, commercial, and industrial applications.
DIN-rail mounting — 45 mm width per pole, compatible with any standard DIN-rail enclosure.

For B2B projects that ship to multiple regions, the FAZ family’s dual IEC / UL certification simplifies the panel-builder’s BOM — one MCB line covers both markets.

2. FAZ Trip Curves: The Six Characteristics

The Eaton FAZ circuit breaker trip curve defines how quickly the breaker opens under overload. Each curve is tuned for a specific load type. Choosing the wrong curve is the single most common B2B MCB selection mistake.

Curve	Instantaneous Trip	Typical Application	Common B2B Use
B	3 to 5 × In	Resistive loads, very low inrush	Electric heating, water heaters, lighting (no inrush)
C	5 to 10 × In	Small motors, lighting with inrush	Lighting with LED drivers, small socket outlets
D	10 to 20 × In	High inrush loads	Transformers, large motors with direct-on-line starting, X-ray equipment
K	8 to 12 × In	Industrial motor loads	Motor branch circuits (with separate overload protection)
S	13 to 17 × In	Selective coordination	Upstream MCB in a series with downstream MCBs
Z	2 to 3 × In	Sensitive electronic loads	Semiconductor protection, measuring circuits

Rule of thumb for B2B buyers: when in doubt, choose curve C. It is the most common industrial MCB trip curve and covers the majority of small-motor and lighting loads. Use D only for transformer-fed or very high-inrush loads.

3. FAZ-NA vs FAZ-RT Variants

For international B2B projects, two FAZ variants matter:

FAZ-NA — North American catalog. UL 489 listed for North American installations. Available in 1-pole, 2-pole, 3-pole, and 4-pole configurations with the same IEC 60898 trip characteristics as the standard FAZ.
FAZ-RT — Ring tongue terminal variant. The ring-tongue termination is preferred in industrial panels because it provides a more secure connection under vibration than the standard box clamp. Common in mining, marine, and heavy industrial applications.

Common FAZ B2B catalog numbers:

FAZ-B6/3 — Curve B, 6 A, 3-pole
FAZ-C10/3 — Curve C, 10 A, 3-pole
FAZ-C16/1 — Curve C, 16 A, 1-pole
FAZ-C32/3 — Curve C, 32 A, 3-pole
FAZ-D7/2-RT — Curve D, 7 A, 2-pole, ring tongue
FAZ-K20/3 — Curve K, 20 A, 3-pole (industrial motor branch)

Browse the full Eaton FAZ circuit breaker catalog at eatonty.com for the complete list of available configurations.

4. Sizing the FAZ MCB Correctly

Three rules for sizing an FAZ correctly:

Continuous load current must not exceed 80% of the MCB rating (per IEC 60898). For a 10 A MCB, the maximum continuous load is 8 A.
Short-circuit current at the MCB’s location must be less than the MCB’s breaking capacity (typically 10 kA or 15 kA for residential, 25 kA for industrial). For higher fault currents, consider NZM molded case circuit breakers upstream.
Selective coordination — the upstream breaker must clear the fault before the downstream breaker if you want to maintain power to the rest of the installation during a fault. Use curve S (selective) on the upstream FAZ to enable this.

For B2B project planning, the most common mistake is oversizing the MCB. A 32 A MCB on a 28 A continuous load will nuisance-trip under normal operation. Choose the rating at 1.25 to 1.5 times the continuous load current.

5. FAZ Accessories

The FAZ family accepts a complete range of accessories that B2B panel builders should know about:

Auxiliary contact blocks — FAZ-XHIN or FAZ-XHIKI, for remote status indication
Shunt trips — FAZ-XAA or FAZ-XAA-NA, for remote tripping
Undervoltage releases — FAZ-XUA, for emergency stop circuits
Busbar systems — Eaton EVG busbars, for fast multi-pole FAZ assembly

These accessories are stackable on the FAZ body without taking additional DIN-rail space, which is a key advantage in dense panel designs.

6. How the FAZ Compares to Other Eaton MCBs

For B2B buyers familiar with other Eaton MCB families, the FAZ is positioned between the residential FAZ-PN and the high-fault-current NZM molded case range:

Family	Range	Trip Curves	Best For
FAZ-PN	2 A to 40 A	B, C	Residential / light commercial
FAZ	0.5 A to 63 A	B, C, D, K, S, Z	Industrial / commercial
FAZ-S	0.5 A to 63 A	C, S	Selective applications
NZM	16 A to 1600 A	Thermal-magnetic, electronic	Sub-distribution / feeders

For a related comparison of the larger Eaton molded case circuit breakers, see our Eaton NZM sizing guide.

7. Frequently Asked Questions

What is the difference between FAZ and FAZ-NA?

FAZ-NA is the North American catalog variant, UL 489 listed. Functionally identical to the standard FAZ (which is IEC 60898), but with different certifications and a different catalog numbering convention.

Can I substitute FAZ-B for FAZ-C?

Generally no. Curve B trips at 3 to 5 × In, while curve C trips at 5 to 10 × In. If a downstream motor has high inrush, a curve B MCB will nuisance-trip. Always match the curve to the load type.

What is the maximum short-circuit rating of the FAZ?

The standard FAZ is rated 10 kA or 15 kA at 400 V AC, depending on the catalog number. For higher fault currents, use the FAZ-XKH… or move up to the NZM molded case circuit breaker range.

Do FAZ MCBs work with DC circuits?

Yes — the FAZ-DC family is rated for DC applications up to 250 V DC per pole. The standard FAZ is for AC only.

What is the lead time for FAZ in international B2B orders?

Common FAZ SKUs (FAZ-B6/3, FAZ-C10/3, FAZ-C16/1) are usually in stock for 2 to 4 weeks lead time. Less common variants (curves K, S, Z) may take 4 to 6 weeks.

Conclusion

The Eaton FAZ circuit breaker remains the most reliable MCB for IEC 61439-compliant final distribution. By following the selection workflow — match the trip curve to the load, size the breaker at 1.25 to 1.5 × continuous current, and verify breaking capacity at the installation point — B2B buyers can ensure their panels are properly protected and code-compliant.

For project quotations, technical datasheets, or B2B volume pricing on the Eaton Moeller FAZ family, contact our team or browse the full FAZ product catalog online.