15 Amp plugs and sockets (conforming to BS546) have been the staple connector for the UK's theatre lighting industry for many years. A 3pin connector, the round pins help differentiate the connector from the 13A household version. Similar in size and construction to 13A household connectors, the 15A version is used as the household connector in South Africa. 15A plugs do not have a space for a fuse, as the fuses in lighting systems are generally located within the dimmer. Care must be taken when fitting non-dimmable items with 15A connectors as damage to the item may occur if accidentally connected to a dimmer - in many UK Theatres and other venues, 15A plugs are used for dimmed power, and 16A CEEForms for "Hard Power". This unofficial convention helps prevent connecting sensitive equipment such as moving lights with switch-mode power supplies to dimmers, which can damage the connected equipment or the dimmer itself.
15A plugs should be wired in the same way as a 13A plug. Always remember to slide the plug top over the cable before wiring to the terminals. If you forget "To Duraplug", don't cut the bit out of the plug top, rewire it again properly.
Grelco is the common name for the two way adaptors used to connect two 15A plugs into one 15A socket. Three-way versions are called Trelcos.