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Ferrules Can Be Used for Better Electrical Connections


If the spread of bare strands of wire is creating a problem in an electrical product, using a ferrule can help make a better connection.

Ferrules offered by Interpower come in two styles—insulated and uninsulated. The insulator, which helps to eliminate arcing in the assembly, is added to the “top” of the ferrule.

Uninsulated Ferrule  Insulated Ferrule  Double-Wire Insulated Ferrule
 82031120_1.5  82031260_6  82031510_10 DBL ferrule

Ferrules are sized by metric measurement, so international wire sizes will fit properly in the ferrules. North American conductors are not sized metrically, so the metric size of North American conductors is approximate. For example, 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 the next size larger will be needed. (See Ferrules for more details.)


Selecting a Ferrule

Consider these factors when selecting the kind of ferrule to use.

  • Determine if insulated or uninsulated is best for the application.
  • Determine if the application requires a double-wire (insulated) ferrule and is designed to accept only two wires.
  • Identify the conductor size. Insulated ferrules are color coded, while uninsulated ferrules are not. The colors correspond to the rated wire size and each code uses different colors for individual sizes.
  • To convert from metric sizes to AWG sizes, see Interpower’s Metric Conversion Guide.


Securing Connections with a Ferrule

Using a ferrule can help ensure all of the individual wire strands will conduct current properly.


If the wire is stranded, the individual strands may move out of the way of the screw as it is tightened. An electrically acceptable connection may or may not exist.   


Crimping the ferrule is one way to ensure a solid electrical connection. The ferrule needs to be sized properly so it slides onto the wire easily. The wire should fill at least 80% of the ferrule.

An insulated ferrule can help minimize the chance of a loose strand causing a short circuit.



For proper installation, Interpower recommends using a tool specifically designed for crimping ferrules.


Additional Resources

For more details, see Ferrules and the Ferrule Selection Guide.

Interpower offers a 1-week U.S. manufacturing lead-time on non-stock Interpower products, same day shipping on in-stock products, and no minimum order or dollar requirements. Blanket and scheduled orders along with value-added services are available. If you have questions, Interpower offers free technical support. You can check the website at, e-mail (United States) or (United Kingdom) or contact Customer Service in the United States at (800) 662-2290 or in the United Kingdom at +44 (0)1908 295300.

Free NEMA Nomenclature Chart

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Interpower Components Ltd.  10 Kelvin Drive  Knowlhill  Milton Keynes  Buckinghamshire  MK5 8NH  United Kingdom

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