A ferrule is an internal component that is used for better electrical contact in applications where the spread of bare strands could cause a problem. Ferrules are types of objects that are used for fastening, joining, sealing or reinforcement. Interpower ferrules come in uninsulated wire ferrules, insulated wire ferrules, or double wire ferrules.
For part numbers see the Ferrule Selection Guide.
Ferrules come in two styles—insulated and uninsulated. The insulator is added to the “top” of the ferrules. The insulator helps to eliminate arcing in the assembly.
|Uninsulated Ferrule||Insulated Ferrule||Double-Wire Insulated Ferrule|
The ferrules are sized by metric measurement, so international wire sizes will fit properly in the ferrules. North American conductors are not sized metrically. 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. The 1.00 size ferrule will allow the 0.82 conductor to fit and permit 80% of the conductor to fill the ferrule space. Metric sizes do not include 2.00mm2. It moves from 1.50 to 2.50mm2. This affects 14 AWG conductors whose measurement is 2.09mm2. The only solution is to use 2.00mm2 ferrule and make do with the crimping.
In selecting the kind of ferrule to use, there are several factors that should be considered.
- It needs to be determined whether it will be insulated or uninsulated for the application.
- It needs to be determined if the application requires a double-wire ferrule, which is an insulated version and is designed to accept only two wires.
- If two AWG wires of the same size are being used, then the correct ferrule size can be determined by increasing the total wire size by three steps. For example, two 20 AWG wires (cross sectional area of 0.519mm2 each) are equivalent to a single 17 AWG/1.04mm2, so a 1.5mm2 capacity ferrule should be specified. In theory, two 20 AWG wires might fit into a 1.0mm2 capacity ferrule, but it is likely to be a tight fit.
- If using two metric wires, two 0.75mm2 wires will fit comfortably into a 2 x 0.75mm2 ferrule.
- The conductor size needs to be identified. There may be a need to convert from metric wire sizes to AWG sizes. (For reference: Metric conversion guide.)
- The length of the barrel needs to be determined. Three lengths are available: normal, medium, and long. The actual length varies, depending on the wire size capacity of the ferrule. Most applications require the normal length; however, longer barrels are available in most sizes. For more details, see the Ferrule Selection Guide.
- Insulation offers the opportunity to color code the connection. Uninsulated versions are not color coded. It is important to make sure to select the correct color coding system. There are three different color coding systems offered by Interpower—DIN, T, and W. The colors correspond to the rated wire size and each code uses different colors for individual sizes. The stock color for the ferrule insulator is based on the DIN (Deutsches Institut für Normung) system. The color coding is arranged according to DIN 46228 Teil 4. Other color schemes are available by special order with a minimum quantity of 1,000 pieces and a lead-time of 4-6 weeks.
- Ferrules are typically made of tin-plated copper and the insulation is a polyamide. The temperature rating is 110°C (230°F).
Although ferrules are commonly used in Europe, they are not well known in North America. Part of the reason is that much of the equipment production in Europe is focused on machinery. Interconnections in machinery are usually based on terminal blocks and other connections that make screw connections desirable. In North America (where electronic equipment production focuses on computers, telecommunications, and medical equipment) interconnections are typically very small and terminal blocks are inappropriate in many cases. These devices are usually approved in Europe as part of the equipment. They do not have separate approvals. In North America, they are also subject to evaluation at the time the equipment is evaluated by UL and CSA for certification.