Terminal block connections, recommended practice

The following recommendations apply to spring and screw cage terminal blocks (TBs).

Wire ferrules

Wire ferrules are recommended for both stranded and solid wire, to prevent contact loss due to oxidation and wire deformation. In the case of stranded wire, ferrules also prevent shorts caused by splayed or broken strands.

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  Wire ferrule crimped onto a stranded conductor

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  Use a twin wire ferrule such as this to connect two wires to a common terminal

When choosing a ferrule, make sure:

• Ferrule inside diameter is large enough to accommodate the wire.
• Ferrule outside diameter is not too large to fit into the TB.

A crimping tool is used to secure the wire to the ferrule. Use the proper tool, which will crimp without damaging the ferrule and leave a textured surface that is readily gripped by the terminal.

To assemble, insert the wire (or wires, in the case of a twin ferrule) into the ferrule and crimp. Insert the crimped ferrule into the TB and tighten it in place.

Stranded wire

• Do not insert bare strands directly into the TB.
• Do not apply solder to the strands.
• Use a wire ferrule. Insert the strands into the ferrule and crimp to make a solid end. Insert the ferrule into the TB.
• Provide a strain relief if the wire will be flexed or subjected to pulling forces.

Solid wire

• The use of a wire ferrule is optional.
• It may be acceptable to insert bare wire into the TB. This should be avoided if the wire is subjected to vibration or pulling forces, or if the wire would be significantly deformed by the compressive force of the TB jaws.
• Do not flex the wire after installation.

Strain relief

It is recommended to secure all wires with strain reliefs. This is especially important if the wires will be subjected to vibration or pulling forces.