Read a power-terminal derating curve with its mating parts, neighboring contacts and wiring conditions. Use the relevant local ambient temperature and check the PCB assembly's other limits. A room-temperature current rating is not a high-temperature rating, and a corrected curve should not receive an assumed second universal reduction.
Identify the components represented by the curve
IEC 60512-5-2 describes elevated-ambient current capacity for electromechanical components, mainly connectors. Phoenix Contact explains the influence of adjacent contacts, contact material and insulating housing.
Obtain a curve for the exact product and mating combination. Review position count, loaded contacts and conductor cross-section against board copper, wiring and cooling. Do not transfer a plug-in connector curve to bare SMT copper hardware without justification.
Distinguish base data from a corrected derating curve
Phoenix Contact describes thermal-equilibrium measurements at different currents, base curves and their correction. Ask the supplier which stage the supplied plot represents and which manufacturing or measurement effects its factor includes.
Record curve revision, temperature location and the selected permissible current. The equipment designer should establish any additional margin. Do not repeat an included correction or turn a manufacturer's example temperature limit or factor into a rule for all PCB hardware.
Confirm the limiting element on the actual board
We recommend representative wiring and neighboring-component conditions, recording local ambient and critical temperatures. Review contacts, insulation, soldering and PCB paths against their respective limits. External room temperature is not automatically the local terminal ambient inside an enclosure.
Review continuous, pulse and fault loads separately. A continuous derating curve does not establish short-circuit endurance or pulse life. Reassess coverage after changing wires, position count, mating parts or cooling, adding assembly validation where needed.
- Match product and loaded contacts
- Identify included corrections and temperatures
- Check terminal, solder and PCB limits
Frequently asked questions
Can a one-loaded-contact assembly use a fully loaded multi-position curve? Confirm the original and actual arrangements rather than scaling by contact count.
Can bare SMT busbars use connector derating plots? Different structures and limits need assembly-specific evidence.
RFQ inputs for current selection
Supply product and mating IDs, wiring, cross-section, board stack-up and cooling. Define continuous/pulse loads and local temperature range, requesting matching curves and test conditions. Review specimens when evidence is absent rather than promising one current rating or reduction rate.
Apply this guide to a project
Use product pages to identify the hardware family and the calculator for early estimates only. Acceptance depends on drawings, operating conditions and project tests.