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Metal halide and high-pressure sodium lamps feature extremely different bases, which include RX7s, Fc2, G8.5, GX8.5, GX10, G12, GX12, PG12, PGJ5, GU6.5, E27 and E40, depending on whether the lamp is single- or double-ended. All lampholders are subject to the same typical conditions found with discharge lamps: high ignition voltages and temperatures. The high start-up currents deserve particular attention in lampholder design. This is also reflected by the insulation materials, which are usually solid ceramics or heat-resistant plastic (e.g. PPS – polyphenylene sulphide).
Depending on the lamp´s requirements (voltage, current, temperature, etc.), silver, nickel and copper alloys with thick nickel coatings are used as conductors. The luminaire regulation EN 60598–1 (VDE 0711 part 1), defines the safety requirements with regard to ignition voltages in connection with creepage and air clearance distances.
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Special care must be taken to ensure that lampholders are approved for discharge lamps when using high-pressure lamps with E27 and E40 Edison bases. Lampholders that are suitable for this purpose are marked with a maximum value of "5 kV" and comply with the increased creepage and air clearance distances specified by the lampholder requirements in EN 60238 (VDE 0616 part 1). The lampholder regulations governing special lampholders, EN 60838 1 (VDE 0616 part 5), apply analogously to all other base systems. The high ignition voltage pulses also place special demands on the conductors. In practice, silicone-insulated conductors with an outer diameter of 3.6 mm have proved to be suitable for discharge lamps. Silicone-insulated conductors with a glass-silk lining with a diameter of 7 mm should be used for lamps with an instant hot restart (20 kV) function.
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