Edison Screw - Types

Types

Dimensions and tolerances for screw bases are standardized in ANSI standard C81.67 and IEC standard 60061-1. The two standards have mostly been harmonized, although several types exist in only one of the two standards with no equivalent in the other.

The designation Exx refers to the diameter in millimeters (i.e., E12 has a diameter of 12 mm.) Do not confuse this with the bulb glass size which in the U.S. is given in eighths of an inch (i.e., MR16, T12). There are four common sizes of screw-in sockets used for line-voltage lamps:

  • Candelabra: E12 North America, E11 in Europe
  • Intermediate: E17 North America, E14 (Small ES, SES) in Europe
  • Medium or standard: E26 (MES) in North America, E27 (ES) in Europe
  • Mogul: E39 North America, E40 (Goliath ES) in Europe.
Other screw thread sizes exist for other uses.

The large E39 "Mogul" base is used on street lights, and high-wattage lamps (such as a 100-/200-/300-watt three-way) and many non-incandescent high-intensity discharge bulbs. In areas following the National Electrical Code, general-use lamps over 300 W cannot use an E26 base and instead use the E39 base, 300 W lamps may use either base. Medium Edison screw (MES) bulbs for 12 V are also produced for recreational vehicles. Large outdoor Christmas lights use an intermediate base, as do some desk lamps and many microwave ovens. Previously, emergency exit signs also tended to use the intermediate base, but U.S. and Canadian rules now require long-life and energy-efficient LED lamps, which can be purchased inside a bulb as a retrofit. A medium screw base should not carry more than 25 amperes current; this may limit the practical rating of low voltage lamps.

In countries that use 220–240 volts AC domestic power, standard-size E27 and small E14 are the most common screw-mount sizes, although the BC bayonet cap is often used in France, British and Commonwealth countries. In 120-volt North America and 100-volt Japan, the standard size for general-purpose lamps is E26. E26 and E27 usually are interchangeable.

E12 is typically used for candelabra fixtures. E17 is also sometimes used, especially in small table lamps and novelty lighting, and occasionally the lights on newer ceiling fans. Christmas lights use various base sizes E17 for C9 bulbs, E12 for C7 bulbs, E10 for decades-old series-wired C6 bulb sets in the U.S., and an entirely different wedge base for T1¾ mini lights. For a short time early on, these mini lights were manufactured using E5 screw bases.

A tiny E5 or E5.5 size is used only for extra-low voltages, such as in interior illumination for model buildings, and model vehicles such as model trains. These are often called "pea bulbs" if they are globe-shaped, but they commonly look like mini Christmas bulbs, or large "grain-of-wheat" bulbs. E10 bulbs are common on battery-powered flashlights, as are bayonet mounts (although those are usually held in with a circular flange located where the base meets the bulb). The E11 base is sometimes used for expensive 50/75/100-watt halogen lights in North America, where it is called the "mini-can", and tighter threads are apparently used to keep them out of E12-base nightlights and other places where they could start a fire.

There are also adapters between screw sizes, and for adapting to or from bayonet caps. A socket extender makes the bulb stick out further, such as to accommodate a compact fluorescent lamp with a self-ballast that don't fit in a recessed lighting fixture.

Read more about this topic:  Edison Screw

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