Whirlwind HBL400F Female AC Connector

The HBL400F is a Hubbell single pole female connector. Single pole connectors are how large feeder is landed on a distro, one conductor at a time, and the colour is not decoration: it is how the phases, the neutral and the ground are told apart on a dark loading dock.

Whirlwind stocks it in black, blue, green, red and white. The colour code is appended to the part number, so HBL400FBK is the black one.