IEC 60309 (formerly IEC 309, also published by CENELEC as EN 60309) is an international standard from the International Electrotechnical Commission (IEC) for “plugs, socket-outlets and couplers for industrial purposes”. The highest voltage allowed by the standard is 690 V DC or AC; the highest current, 125 A; and the highest frequency, 500 Hz. The temperature range is −25 °C to 40 °C.
There is a range of plugs and sockets of different sizes with differing numbers of pins, depending on the current supplied and number of phases accommodated. The fittings also include limited (IP44) weather-proofing, that is one reason for choosing these fittings when the connections will be used in open-air conditions; a further reason for using these (other than when the heavy-current or three-phase facilities are actually needed), is to deter potential users from connecting domestic appliances to the sockets, as ‘normal’ domestic plug-tops will not fit.
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