Contact Sales & After-Sales Service

Contact & Quotation

  • Inquire: Call 0086-755-23203480, or reach out via the form below/your sales contact to discuss our design, manufacturing, and assembly capabilities.
  • Quote: Email your PCB files to Sales@pcbsync.com (Preferred for large files) or submit online. We will contact you promptly. Please ensure your email is correct.
Drag & Drop Files, Choose Files to Upload You can upload up to 3 files.

Notes:
For PCB fabrication, we require PCB design file in Gerber RS-274X format (most preferred), *.PCB/DDB (Protel, inform your program version) format or *.BRD (Eagle) format. For PCB assembly, we require PCB design file in above mentioned format, drilling file and BOM. Click to download BOM template To avoid file missing, please include all files into one folder and compress it into .zip or .rar format.

Fusing Current Estimator - PCBsync

Fusing Current Estimator

PCBsync Engineering Tools
⚠ Overcurrent
Trace Parameters
Trace Width 0.25 mm
Copper Weight 1 oz/ft²
Fusing Time 1 s
Ambient Temperature 25°C
Copper Melting Point 1083°C
Safety Derating 50%
Fusing Analysis
Fusing Current (Onderdonk)
12.4
Amperes
Melts in 1.0 seconds at this current
Recommended Max Operating Current
6.2 A
With 50% safety derating
Cross Section
8.75 mil²
I²t Rating
154 A²s
Current Density
1420 A/mm²
Energy to Fuse
2.6 J/mm
+ − Current: 0A 25°C
Safe Zone
<50% Caution
50-80% Danger
>80%
Current vs Fusing Point 0% of fusing
0% 50% (Safe) 80% (Max) 100% (Fuse)
Warning: Fusing current calculations are estimates based on Onderdonk's equation. Actual fusing depends on PCB construction, solder mask, airflow, and trace geometry. Always include substantial safety margins and verify with testing for critical applications.
Trace Specifications
0.25mm wide × 35µm thick (1oz) copper trace. Cross-sectional area: 0.00875 mm² (13.6 mil²). Onderdonk constant k = 12,706 for copper at 1083°C melting point.

Understanding Trace Fusing Current

The fusing current is the current level at which a PCB trace will heat up enough to melt the copper, causing an open circuit. This is critical for designing PCB fuses, understanding failure modes, and ensuring traces can handle fault currents. Unlike steady-state current capacity, fusing is an adiabatic process — heat builds up faster than it can dissipate.

Ifuse = A × √[(ΔT × k) / t]   where   k = ln(1 + (Tm - Ta) / (234 + Ta))

This is Onderdonk's equation, where A is cross-sectional area (circular mils), t is time in seconds, Tm is melting temperature (1083°C for copper), and Ta is ambient temperature. The constant 234 relates to copper's temperature coefficient of resistance.

Derating Guidelines
  • 20% — Fuse applications (intentional blow)
  • 50% — General safety margin
  • 70% — Conservative design practice
  • 80% — Maximum for any continuous current
Time Dependencies
  • 1ms — ESD/transient events
  • 10ms — Circuit breaker trip time
  • 100ms — Fast-blow fuse reference
  • 1-10s — Slow-blow fuse / sustained fault
PCB Fuse Design
  • Use narrow neck (0.1-0.2mm) for defined blow point
  • Remove solder mask over fuse area
  • Keep fuse away from other traces
  • Consider arc containment for high voltage
I²t (Let-Through Energy)
  • Measures total energy during fault
  • Must be less than trace I²t rating
  • Upstream protection must clear faster
  • Coordinate with fuse/breaker ratings

Design Note: For intentional PCB fuses, target 20-30% of calculated fusing current for reliable operation. The trace will heat significantly before fusing, potentially damaging nearby components. Always isolate PCB fuses with keep-out zones and consider adding thermal relief patterns.

Contact Sales & After-Sales Service

Contact & Quotation

  • Inquire: Call 0086-755-23203480, or reach out via the form below/your sales contact to discuss our design, manufacturing, and assembly capabilities.

  • Quote: Email your PCB files to Sales@pcbsync.com (Preferred for large files) or submit online. We will contact you promptly. Please ensure your email is correct.

Drag & Drop Files, Choose Files to Upload You can upload up to 3 files.

Notes:
For PCB fabrication, we require PCB design file in Gerber RS-274X format (most preferred), *.PCB/DDB (Protel, inform your program version) format or *.BRD (Eagle) format. For PCB assembly, we require PCB design file in above mentioned format, drilling file and BOM. Click to download BOM template To avoid file missing, please include all files into one folder and compress it into .zip or .rar format.