Ferrules are internal electrical components that ensure electrical continuity in applications where the splay of bare wires may cause connection issues, preventing accidental contacts and short circuits. They also protect the wire from damage when using compression screw, spring, or split-bolt connectors.
Interpower ferrules come in two styles—insulated and uninsulated. The insulated versions protect the assembly from arcing and is added at the “top” of the ferrule. All Interpower ferrules are tin-plated copper and have a temperature rating of 120° Celsius—all are RoHS and REACH compliant. For proper installation, Interpower recommends using a tool specifically designed for crimping ferrules onto wires.
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Insulated Ferrule |
Double-Wire Insulated Ferrule |
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Ferrules are sized in millimeters for international wire sizes to fit properly into the ferrules. North American conductors are sized in American Wire Gauge (AWG), so the metric size of North American conductors is approximate. For example, an 18 AWG conductor is approximately 0.82mm². The size is between the metric 0.75 and 1.00mm². A ferrule meant for 0.75 will be too small, so a larger size will be needed. (See Ferrules for more details.)
Selecting a Ferrule
In selecting the right type of ferrule there are several factors to consider:
- Does it need to be insulated or uninsulated for the application?
- Does the application require a double-wire ferrule? This is an insulated version designed to accept only two wires.
- The conductor size needs to be identified. There may be a need to convert from metric to AWG sizes. See the Metric Conversion guide for more information.
Insulated ferrules can be color coded while uninsulated ferrules cannot. The colors correspond to the rated wire size, and each code uses different colors for individual sizes. Interpower stock color for the ferrule insulator is based on the DIN (Deutsches Institut fur Normung) system. The color-coding is arranged according to DIN 46228 Part 4.
Securing Connections with a Ferrule
Using a ferrule can help ensure all individual wire strands will be conducting current properly.
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If the wire is stranded, the individual strands may tend to move out of the way of the screw as it is tightened. An electrically acceptable connection may or may not exist.
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One way to ensure a solid electrical connection is to crimp the ferrule. It is important that the ferrule is sized properly so that it slides onto the wire easily. The wire should fill at least 80% of the ferrule.
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An insulated ferrule can help minimize the chance of a loose strand causing a short circuit.
