The cores of flexible PROFIBUS cables consist of many fine strands. In general, stranded cores should be fitted with wire-end ferrules (boot-lace ferrules) to keep the strands together and prevent them shorting. In many cases, however, the screw terminals on PROFIBUS components are designed to directly accept stranded cable without wire-end ferrules. To determine whether the screw terminals can directly accept stranded cable without a ferrule, you should compare the terminals with the following two figures. However, you should always follow the terminal manufacturer’s instructions.
Fig.: Screw terminals – suitable for stranded cables without wire-end ferrules
However, terminals where only one screw pushes onto the core from the top are not allowed without wire-end ferrules.
Fig.: Screw terminals – not suitable for stranded cables without wire-end ferrules
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The following must be observed in the use of wire-end ferrules:
It is best to use plated copper wire-end ferrules. Never use wire-end ferrules made from aluminum!
Use wire-end ferrules that fit the cross section of the cores. Incorrectly fitting wire-end ferrules lead to a bad contact.
Ensure that the length of the wire-end ferrules is completely filled. If the wires end before the end of the wire-end ferrules, additional insulation must be removed..
Do not twist the strands before inserting into the wire-end ferrule. Leave the strands straight.
Crimp the wire-end ferrules only with crimping pliers with positive lock. Positive lock means that the crimping pliers can only be opened if the wire-end ferrule was completely crimped.
Never use any other pliers or cutters for crimping. They do not exert sufficient crimping force. In this case, the contact between wire-end ferrule and core is insufficient. In addition, there is the risk of damaging the cores.
