How Terminal Block Contacts Work

Quick-connect type terminal block contacts consist of a flat blade or a simple tab with a design that accepts a push-on connector holding the end of a wire. A force-fit metal sleeve pushed over the tab makes the contact. Such quick-connect type terminal blocks are meant for thin wires up to AWG 12.

Tubular contacts are a length of rectangular metal tubing, with screws threaded through the top of the tube at both ends. In tubular screw contacts, the flat bottom of the screws secures the inserted wires by providing pressure on them. Tubular clamp contacts use a pressure plate between the screws and the wire to apply pressure on the wires. The screws usually hold the pressure plates captive, which makes tubular clamp contacts useful for fine stranded wires.

Feed-through contacts have mounting surfaces with studs going through them. Feed-through contacts are useful for wire leads passing through a wall under a block directly or very close to the wall. Stud contacts or strap-screws secure the wires for connection.

For installations that must stay connected even during shock and vibration, dead-front connectors with two-part plug-ins are very useful. For multiple points of contact on posts, quality connectors typically use socket-mating springs. Wire protectors made of beryllium-copper protect both single and multi-stranded wire terminations. Flush-mount designs for boards are best for minimizing stress on solder joints when tightening screw terminals.

Flat metal strap with screws through each end make up strap-clamp contacts. The screw heads usually have a wire-clamping element under them for exerting pressure on the wires. These contacts require the insertion of bare wires within the pressure contact.

Strap-screw contacts are similar in construction to the strap-clamp contacts but without the wire-clamping elements. The user simply loops the wires over the screws or may attach a ring or spade lug on them. Tightening the screws on the loop, ring, or spade lug serves to secure and connect them.

Fuse blocks usually consist of a fuse in series with a circuit. Usually, there are contacts at each end, like that of standard blocks. It is possible to insert a cartridge-fuse pug into clips connected to each contact. Apart from circuit identification, this arrangement facilitates easy fuse changing.

Plane and rigid insulating members can mount multiple one-piece blocks for connecting one or more circuits. There may be open barriers facilitating easy contact accessibility. Other variants may offer contact protection through closed barriers or dad fronts. A single base may hold standard units of 2, 4, 6, 8, 10, or 12 circuits.

Terminal block contacts may also be of the short-circuit type, like the one-piece blocks. Short-circuit contacts require a screw short-circuiting two strips, allowing current flow into the desired circuit by direct connection or by shunting out other circuits.

Section blocks usually come with individual molded units containing contacts. It is possible to form any desired number of circuits by assembling them together with end barriers in between. Formation of preassembled lengths requires snapping off or adding sections in the desired number of groups of contact sections to form a sectional terminal block assembly.