How wall power outlets are made

Wall sockets arrived in the 1880s so appliances no longer had to be wired into a light fixture.

stations: 6
things upstream: 47
raw sources: 18
steps from the ground: 7

The short version

Springy contacts start as copper or brass sheet in a high-speed press, which punches, bends and can rivet them in one run. Injection molding machines form the plastic body, at one plant with robot arms placing copper inserts. Assembly lines fit the contacts and terminal screws, and inspections at several stages catch faults before the outlets ship.

Stamp the contacts

A press punches the clips and terminals from metal sheet through a fast continuous die. One supplier holds errors to within 0.01 to 0.05 millimeters, which keeps plug insertion and removal force under control.

Goes in
Brass Copper
Bend and rivet the clips

The same die run bends each clip and can rivet parts together. Fewer gaps between pieces mean less oxidation and loosening later.
Turn the heavy pins

Larger industrial sockets can use machined parts. A maker in Wenzhou, China, turns brass pins and sockets on automatic lathes, with 16A and 32A parts on its high-speed machines.

Goes in
Brass
Mold the housing

Plastic is injected into molds to form the face and body. The Wenzhou plant runs 50 machines from a central feed of flame-retardant engineering plastic, with five-axis robot arms placing copper inserts and chilled water cooling the work.

Goes in
Plastic
Fit parts together

Contacts are fitted in the body, terminal screws go in, and the face is fixed on. Modern plants run this on assembly lines, and the Wenzhou maker describes its assembly as automated.

Goes in
Screw
Inspect at every stage

Inspections run at several points in production, so a bad socket is caught early and corrected. Safety tests come first in design and carry on through manufacturing, because an electrical failure can do serious harm.

End of the linePower outlet

Worth repeating

In the 1880s, appliances stopped borrowing light fittings once the first wall sockets and plugs reached the market.
Commercial electric power was sold mainly for lighting at first, which is why the earliest appliances connected to light sockets.