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IEC 60238: Edison Screw Lampholders — The Safety Standard Behind Billions of Light Sockets Worldwide
Every Bulb Fits Every Socket — The Polarity, Contact Resistance, and Heat Endurance Behind E14/E27/E40
IEC 60238 specifies Edison screw lampholder (E14/E27/E40) requirements. The safety of billions of lampholders — from insulation heat resistance to electric shock protection — depends on this standard.
| Safety Element | Requirement | Design Principle |
|---|---|---|
| Polarity Rule | Center contact MUST be Live(L), screw shell MUST be Neutral(N) | Prevents accidental finger contact with live screw during bulb replacement |
| Contact Resistance | Center contact-to-cap ≤0.05 Ω | Excess resistance → local heating → carbonization → fire |
| Thermal Endurance | Holder material must not soften/deform under prolonged heat | LED bulb base doubles as heat sink; temps can exceed 120°C |
The LED-era lampholder challenge: An incandescent bulb base was purely a mechanical interface. An LED bulb base is also a thermal conduction path — a 15 W LED (equivalent 100 W incandescent) can reach base temperatures exceeding 120 °C. IEC 60238 requires holder materials to withstand this temperature long-term without softening, deforming, or releasing combustible gases. This places stricter demands on lampholder plastics (PBT, PET, PA) thermal ratings.
TN Lab — One lampholder safety standard protects billions of households from electric shock and fire.
