Ferrules

  • Ferrules are sold in 100 count boxes
  • Same day shipment on in-stock products


Download a list of Interpower ferrules in a PDF format

Selecting Ferrules

The first step in selecting a ferrule is to select the style that is appropriate for the application and specifically whether the ferrule is to be insulated or uninsulated. Insulated ferrules are slightly more expensive; however, insulated ferrules “capture” strands that do not get correctly inserted into the barrel, thereby reducing the possibility of a short between connections. Insulation also offers the opportunity to color code the connection.

The second step in selecting a ferrule is to identify the conductor size. There may be a need to convert from metric wire sizes to AWG (American Wire Gauge) sizes. See the Metric Conversion Guide for more information.

The third step in selecting a ferrule is to determine how long the barrel should be. Three lengths are available: normal, medium, and long barrels. The actual barrel length varies depending on the wire size capacity of the ferrule. Most applications require the normal length; however, ferrules with longer barrels are available in most sizes.

The fourth step in selecting a ferrule is to select the ferrule color coding system you want to use. There are three different ferrule color coding systems available. Our 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 Teil 4. (Note: Uninsulated ferrules are not color coded.) Other color schemes are available by special order with a minimum quantity of 1,000 pieces and a lead-time of four to six weeks.

The fifth step in selecting a ferrule is to determine if the application requires a double wire ferrule. Double wire ferrules are available only in insulated versions and are designed to accept only two wires. If you are using two AWG wires of the same size in a ferrule, you can determine the correct ferrule size by increasing the total wire size by three steps. For example, two 20AWG wires (cross sectional area of 0.519 mm2 each) are equivalent to a single 17AWG/1.04 mm2. Therefore, you would specify a 1.5mm2 capacity ferrule. In theory, two 20AWG wires might fit into a 1.0mm2 capacity ferrule, however, they are likely to be a tight fit. Per UL 1581, table 20.1

If you are using two metric wires, two 0.75mm2 wires will fit comfortably into a 2 x 0.75mm2 ferrule. The ferrules are made of tin plated copper, and the insulation is a polyamide. The temperature rating is 110°C.

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 centers around 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.

Why use Ferrules Back to top

Screw Connections:
Contacts found in large industrial connectors and many terminal blocks use a screw to secure the connection between the wire and contact (Figure 1).

Easier Insertion:
With ferrules, there is easier insertion of the wire into the female receptacle: individual wire strands will not fray backwards ensuring better guarantee that all strands will be conducting current.

Unsecure Connections:
If the wire is stranded, the individual strands will tend to move out of the way of the screw as it is tightened (Figure 2).

If the wire is just slightly smaller than the opening in the contact, the screw will usually clamp several of the strands securely while the others move up along-side the screw. However, if the wire normally fills two-thirds or less of the opening in the contact, the screw may bottom out with none of the strands securely gripped. At this point, an electrically acceptable connection may exist, at least long enough for the device to be tested and shipped to the customer. However, the slightest vibration may allow the screw to back out enough that the impedance of the connection increases so that excess heat is generated. The connection could become intermittent.

Some contacts are designed to address this issue by including a contact tang (Figure 3). This type of contact will normally assure that all strands are captured and are in contact with the screw connection. If the contact does not offer a contact tang, a crimp ferrule is the best way of assuring a solid contact (Figures 4 and 5). The ferrule should be sized properly so that it slides onto the wire easily. However, the wire should fill at least 80% of the ferrule. The ferrule is then crimped and inserted into the contact and the screw tightened. An insulated ferrule minimizes the chance that a loose strand can cause a short circuit.

Back to top