Skip to main content
ECalPro
Try Free

MCB Tripping Curves Pocket Card — B, C, D Curves Reference

Instant reference card for MCB tripping curves (B, C, D types). Shows magnetic & thermal trip thresholds per IEC 60898. Free printable PDF.

Multi-Standard4 min readUpdated March 3, 2026
Share:

Credit-card size (85.6 × 54 mm), double-sided, 250–300 gsm coated cardstock, gloss or matte lamination both sides. CMYK colour mode. QR code minimum 12 × 12 mm linking to ecalpro.com/calc/protection.

ParameterValue
Dimensions85.6 mm × 54 mm (ISO/IEC 7810 ID-1)
Bleed3 mm all sides (final trim: 91.6 × 60 mm)
Safe zone3 mm inside trim (content area: 79.6 × 48 mm)
Stock250–300 gsm coated cardstock

Front — Magnetic Trip Ranges & Visual Curve Comparison

Simplified Trip Curve Description

The trip curve is a log-log chart with current (as multiple of In) on the X-axis and trip time on the Y-axis. All MCB types share the same thermal region:

  • At 1.13 × In: Must NOT trip within 1 hour (cold start)
  • At 1.45 × In: MUST trip within 1 hour (cold start)

The magnetic trip bands are the key differentiator between types:

  • Type B (green band): Instantaneous trip between 3× and 5× In
  • Type C (amber band): Instantaneous trip between 5× and 10× In
  • Type D (red band): Instantaneous trip between 10× and 20× In

Magnetic Trip Range Summary

TypeMagnetic Trip RangeGuaranteed Trip
B3× In to 5× InMust trip at 5× In
C5× In to 10× InMust trip at 10× In
D10× In to 20× InMust trip at 20× In

Worked Example

Example: 32 A Type B MCB

  • Magnetic trip range: 96 A to 160 A
  • Guaranteed instant trip: 160 A (5 × 32 A)
  • Below 96 A: thermal trip only (slower)

Back — Application Guide, I2t Let-Through & Selection Matrix

Application Selection Guide

TypeDesigned ForTypical ApplicationsInrush Tolerance
BResistive and lightly inductive loadsLighting circuits, socket outlets, electric heating, residential generalLow (3–5×)
CModerate inductive loadsSmall motors, fluorescent lighting with EM ballasts, IT equipment, commercial generalMedium (5–10×)
DHeavy inductive loadsLarge motors, transformers, welding equipment, X-ray machines, compressorsHigh (10–20×)

Practical Decision Flowchart

Is the load purely resistive (heaters, incandescent)?
  YES --> Type B

Does the load have moderate inrush (< 10×)?
  (small motors, IT, fluorescent)
  YES --> Type C

Does the load have high inrush (> 10×)?
  (large DOL motors, transformers, welding)
  YES --> Type D

I²t Energy Let-Through Comparison

Reference: IEC 60898-1, Table 11 & 12

Key Insight: A Type D MCB lets through 2–3× MORE energy (I²t) than a Type B during a short circuit. PPE selection should consider MCB type, not just prospective fault current.
Rating (In)Type B I²t (kA²s)Type C I²t (kA²s)Type D I²t (kA²s)
6 A4,5009,00018,000
10 A8,00015,00030,000
16 A18,00030,00055,000
20 A25,00042,00075,000
25 A35,00055,000100,000
32 A50,00075,000140,000
40 A72,000100,000190,000
50 A100,000140,000260,000
63 A140,000190,000350,000

Values are maximum I²t let-through at 6 kA prospective fault current, energy limiting class 3. Actual values vary by manufacturer — always check datasheets.

Peak Let-Through Current (Ip) Comparison

Prospective IscType B Ip (kA)Type C Ip (kA)Type D Ip (kA)
3 kA3.54.56.0
6 kA5.57.010.0
10 kA7.510.015.0

Values are typical for energy limiting class 3 MCBs per IEC 60898-1.

Additional MCB Types (Less Common)

TypeMagnetic RangeRegion / Standard
A2×–3× InNot in IEC 60898 (some European)
K8×–12× InMotor protection (IEC 60947-2)
Z2×–3× InSensitive electronics (IEC 60947-2)
MANo thermal, magnetic onlyMotor short-circuit protection

Data Source References

DataSource
Type B/C/D magnetic rangesIEC 60898-1:2015+A1:2019, Section 8.6.1, Table 3
Thermal trip characteristicsIEC 60898-1:2015, Section 8.6.1, Table 2 (1.13×/1.45× thresholds)
I²t let-through valuesIEC 60898-1:2015, Section 8.6.5, Tables 11–12; typical manufacturer data (ABB S200, Schneider iC60)
Peak let-through currentIEC 60898-1:2015, Section 8.6.5; manufacturer selection guides
Application guidanceBS 7671:2018 Appendix 3; IEC 60364-4-43; Schneider Electrical Installation Guide
Type K/Z/MAIEC 60947-2:2016, Annex K; circuit breaker application guides
NEC equivalentUL 489: Types rated by AIR (ampere interrupting rating) rather than B/C/D curves
Energy limiting classesIEC 60898-1:2015, Section 3.5.8 (Class 1, 2, 3)

Try the Protection Coordination Calculator

Put this methodology into practice. Calculate results with full standard clause references — free, no sign-up required.

Or embed this calculator on your site
Calculate Protection Coordination

Frequently Asked Questions

Type B trips at 3-5 times rated current (resistive loads), Type C at 5-10 times (motor/transformer inrush), and Type D at 10-20 times (high inrush like welding machines). All per IEC 60898-1.
Type B is standard for socket outlets and lighting circuits in most jurisdictions. Type C is used when circuits supply small motors or fluorescent lighting with high inrush.
Yes. Download the PDF, print double-sided on card stock, and cut to credit-card size (85 x 54mm). Laminate for durability. Free to distribute to your team.

Related Resources

Protection Calculator

Calculate protection coordination and device selection online.

Read more

Cable Sizing Methodology

Complete methodology for electrical cable sizing across multiple standards.

Read more

Transformer Fault Current Pocket Card

Printable reference card for transformer fault current calculations.

Read more