IDB-CON-048
Electronics · connectors · current rating · plating
Connector selection
Choosing connectors — the families and where they fit, per-contact current and the derating that bites with pin count, plating and mating cycles, and environment.
Abstract
Connectors are chosen on a handful of axes — current, voltage, contact count and pitch, wire gauge, mating cycles and environment — and then narrowed to a family. The two things engineers most often get wrong are current derating (with pin count and temperature) and plating (gold vs tin for the duty).
Section 1 is the selection axes. Section 2 is connector families. Section 3 is current rating and derating. Section 4 is contact resistance and plating. Section 5 is mechanical and environmental. Section 6 is a checklist.
1.Selection axes
Pin down these before picking a part:
2.Connector families
| Family | Typical use | Note |
|---|---|---|
| 2.54 mm pin header | prototyping, jumpers, ribbon | ~3 A/pin; not for vibration |
| JST SH/ZH/PH (1.0/1.5/2.0) | wire-to-board signal / low power | 1–2 A; PH is the LiPo standard |
| JST XH / VH (2.5/3.96) | wire-to-board power | 3–10 A |
| Molex Micro-Fit / Mini-Fit (3.0/4.2) | board power | 5–13 A |
| Terminal block (3.5/5.0/5.08) | field wiring | 8–15 A+, screw/spring |
| FFC / FPC | flex cables, displays, cameras | low current; ZIF actuators |
| Barrel / XT60 / Anderson | DC power input | 5–60 A |
| USB / RJ45 / SMA / U.FL | data / RF | controlled impedance (see PCB ref) |
3.Current rating and derating
A connector's datasheet current is usually per contact with a defined temperature rise (often 30 °C) — and it assumes few contacts energized. Derate for reality:
- Pin-count derating: energized contacts heat each other, so the per-contact current drops as more are loadeda 12-way connector might allow only ~70% of the single-contact rating on each. Use the maker's derating curve.
- Temperature derating: the allowable current falls as ambient rises toward the connector's max temp.
- Don't parallel a tiny connector for big current expecting N×; parallel contacts share unevenly.
Total connector current is not N × single-contact rating — size from the derated value.
4.Contact resistance and plating
- Contact resistance (mΩ) causes voltage drop and self-heating; it rises as plating wears and with fretting.
- Plating choice:
- Gold — low, stable contact resistance; many mating cycles; required for low-level signal (it doesn't build insulating oxide). Costlier. - Tin — cheap; fine for power and few mating cycles; prone to fretting corrosion under micro-vibration on signal lines — avoid for low-level signals that move.
- Don't mate gold to tinthe dissimilar pair accelerates wear; match platings.
5.Mechanical and environment
- Mating cycles are plating- and design-limited (tin ~10–50, gold hundreds+). Pick for the service profile.
- Retention / locking (latches, screws, friction) for vibration; add strain relief to the cable.
- Polarization / keying to prevent reversed or offset mating; first-mate/last-break pins for hot-plug power/ground sequencing.
- Sealing (IP) for outdoor/wash-down; vibration wants positive locks and gold contacts.
6.Checklist
- Electrical: per-contact current (derated for pin count + temperature), working voltage, creepage/clearance.
- Mechanical: position count and pitch, wire gauge/termination (crimp/IDC/solder), mating cycles, locking, strain relief.
- Plating: gold for signal/high-cycle, tin for power/low-cycle; match both halves.
- Environment: temperature, vibration, IP sealing, contamination.
- Then pick the family from the table and confirm the derated current against your load (use the Wire gauge & V-drop tool for the conductor).