Socapex is a brand of electrical connectors. Typically, socapex - or soca - refers to 19-pin cables and connectors used for taking power over longer distances.
Socapex connectors can carry 6 individually powered circuits using 6 live and 6 neutral pin pairs on the outer ring and 6 earth pins on the inner ring. The central, 19th pin is used for alignment, along with notches at the bottom of the connector. When correctly aligned, the connectors should be screwed together using the twisting ring on the male connector.
Socapex cables may be connected directly to socapex sockets - for example on the back of the Jands Rack or on IWBs - or may be fanned in or out using a plug or socket spider. Spiders, or tails, have a socapex connector at one end, and 6 15A or 16A connectors at the other.