Slug
Slug turns up in 3 fields: electricians, railroad, shop slang. Here is what it means to the people in each one.
Slug in electricians
Metal disc knocked or punched out of a box or panel, which ends up underfoot and in the bottom of every panel.
A slug is the round piece of steel that comes out of a knockout or is cut by a knockout punch. Slugs collect in the bottoms of panels and boxes and must be cleaned out before energising, because a loose slug can bridge live parts or jam a breaker. Some punches split the slug in two so it falls out of the die instead of having to be pried loose.
"Vacuum the slugs out of that panel before trim, the inspector found three under the neutral bar last time."
Slug in railroad
A heavy, motor-equipped unit without an engine that draws power from a coupled locomotive.
A locomotive chassis heavily ballasted with concrete or steel and equipped with traction motors, but lacking a diesel engine. It is permanently coupled to a normal locomotive, known as a mother, drawing excess electrical power from the mother's main generator at low speeds. Slugs maximize tractive effort and adhesion for heavy drag freight and yard switching without the fuel cost of a second engine.
"We've a pair of GP40s and a yard slug to pull that heavy cut of coal cars up the hump."
Slug in shop slang
A solid piece of scrap metal punched out of a larger sheet or component.
The waste disc or cylinder of material left over after punching a hole, knocking out a port, or drilling through heavy plate. In electrical work, slugs are the metal discs removed from junction boxes to route conduit. In machining, they are heavy offcuts that fall from a punch press.
"Sweep up all those electrical slugs before someone slips on them."