06.07.2022

In both home and industrial wiring, it’s necessary to stick stranded cables into screw terminals or spring connectors. For industrial equipment, hundreds, or even thousands of these connections may be required to automate a task. If just one of these wires comes loose or breaks, you're most likely in for a bit of costly downtime.
Each connection is therefore critical. While the flexibility of stranded wire allows for much easier routing than can be expected from solid-core wire, the ends tend to splay apart. This makes the actual connection to a screw or spring connector a bit of a dicey proposition. In a perfect world, you’d have wire that’s stranded in the middle, and solid on the ends.

Sound like an impossible task? It’s actually possible and easy to implement with the use of ferrule connectors.

Broadly speaking, ferrules are any sort of ring used to either reinforce a shaft or bind together strands of a material. In the context of wiring, a ferrule is a small deformable metal tube, generally made out of tin plated copper. This short tube (or long ring) is placed over a section of stranded wire extending from stripped insulation, then compressed with a crimping tool to hold the strands together. Ferrules discussed here also feature a flared portion on one end, which serves to guide the strands into the main crimped section and provide strain relief.

What Does a Ferrule Do?

Once crimped, the bundle is transformed into what, for practical purposes, acts as the end of a solid-core wire. The addition of the ferrule presents several advantages, including the aforementioned strain relief and the fact that every strand of a wire can now be inserted into a connector, without the fear of a few being displaced to the sides upon insertion. Ferrules greatly reduce the contact resistance between the wire and connector, and even help cut down on the oxidation in the strands because of the lack of air space between them.

Wire Ferrule Color Coding

Ferrules come in a wide variety of different sizes, depending on the wire that you need to crimp, with color codes on the shoulder portion that indicate the size. One possible issue here is that there are at least three different ferrule color codes, which can lead to confusion if different types are mixed. Ideally, you would keep ferrules in the container they came in until used, such the ferrule kit in the above image, removing any doubt about what you’re using.

Know how - Bootlace Ferrules
Using bootlace ferrules is an easy way to improve the reliability of electrical connections when terminating stranded wires. Here's what you need to know from colour codes to types and tips on where to use them.

A ferrule is a tinned copper sleeve which captures the individual strands of a stranded wire. By adding a ferrule to a wire termination, you are essentially giving a stranded conductor the properties of a solid conductor and therefore enabling a more reliable electrical connection. An alternative to using ferrules would be tinning wires with solder. However, the soldering process can damage wire insulation, and is a risky process to perform on-site or alongside other electrical assemblies.

By capturing and fixing the strands together, you can reduce the potential to damage the conductor by screw terminals. Ferrules also make sure all fine strands of copper make it into the connector. By using a defined ferrule pin length conductors can be prepared to the same length required by a chosen connector.

FFerrule colour codes can be very confusing. There are two manufacturer led systems the French system, initially developed by Telemecanique (T), and the German system by Weidmuller (W). Both of these are in everyday use alongside an official German DIN standard.

The Ultimate Guide to Terminal Block Selection
A terminal block consists of a modular housing with an insulated body that secures two or more wires together. Terminal blocks—also referred to as terminal connectors, connection terminals, or screw terminals—are used in a wide array of applications where electrical systems need to be safely connected. They are ideal for designs requiring secure, well-organized, and semi-permanent wire connections that can be easily swapped out for inspection or repair in the field.

There are various types of terminal blocks that can be used in a design. These are some of the most common:

PCB Mount

Often referred to as Eurostyle or wire-to-board terminal blocks, PCB mount terminal blocks work by inserting bare wires into the module where a clamp secures the wire in the housing. The housing is then soldered to a PCB in common footprints. PCB mount terminal blocks can be single, dual, or multi-level modules.

Barrier Strips

These terminal blocks have a screw down terminal where a ring or spade terminal is attached to the wire and then inserted onto the screw and tightened into the housing. Barrier strips are commonly used where vibration is a concern.

Feed-Through

Feed-through terminal blocks are used to connect two wires together for wire-to-wire connections. This terminal block type has one input and one output contact where two distinct wires are fed into opposite sides of the housing. Like PCB mount versions, these can also be single, dual, or multi-level modules.

Key Terminal Block Electrical Considerations

When designing a system that will utilize a terminal block, you will likely know your overall system voltage and current requirements. While these are very important, there are other factors to consider in your design as detailed below.

Current Rating

The current rating is often the most important parameter to consider in terminal block designs. The current rating is based on the conductivity of the terminals, cross-sectional area, and the corresponding heat rise. Operating at too high of a current can cause overheating and damage of the terminal block, leading to major safety concerns. It is best practice to use a terminal block that is rated for at least 150% of the max current that is expected in the system.

Voltage Rating

The voltage rating is in part determined by the dielectric strength and pitch of the terminal block housing. The maximum system voltage of the application must be less than the voltage rating. Any voltage surges in the system should also be evaluated when selecting the terminal block.

What is Ground in Electronic Circuits?
When you start learning about circuits, you’re bound to ask “what is ground?” at one point or another. Are you actually suppose to connect your circuit into the ground??

First of all: grounding in electronics is different from the earth connection in wall outlets (although they sometimes are connected).

I got an email from a reader a little while back:

«The ground symbol keeps appearing at different points in a circuit and I could not understand why a particular place was chosen for grounding. What is ground?»

Grounding something simply means connecting it to ground.

And in electronics, ground is just a name we give to a certain point in the circuit.

For example, in a circuit with one battery (with a positive and a negative terminal), we usually refer to the negative terminal as ground.

And to simplify drawing the circuit, we use a symbol.

So instead of drawing lines to all the places that should be connected to minus, you instead place the ground symbol there. This makes the circuit diagram much cleaner when there are a lot of connections to minus.

To see how the current flows in a circuit diagram with ground symbols, just connect all the points that have ground symbols. That is what you do when you build the circuit.

An Easy-To-Use Combination Four-Terminal-Pair/Two-Terminal-Pair AC Transformer Bridge
A new four-terminal-pair bridge, capable of achieving a relative standard uncertainty of 1×10−9, was constructed at the National Institute of Standards and Technology by converting a two-terminal-pair bridge. The conversion requires only the addition of components which are easily removed if two-terminal-pair measurements are to be made. The design and testing of this bridge is described. The new four-terminal-pair bridge requires fewer auxiliary balances than the present four-terminal-pair bridge employed at NIST, which makes it much easier to use. This new design can be used to compare capacitance, resistance, and inductance standards.

Four-terminal-pair measurements can be made with low uncertainty, (e.g., 0.009 μpF/pF) for a wide range of impedance values. To achieve the same results with two-terminal-pair bridges, extrapolation techniques must be used. Even then, the equivalent uncertainty can only be attained for large impedances, e.g., 10 pF to 1000 pF at 1592 Hz . Four-terminal-pair measurements have the advantages of reducing the effects of parasitic impedances and diminishing the sensitivity to variations in series impedances and shunt admittances in the leads. This is especially important when measuring small impedances. Each four-terminal-pair standard has four terminal-pairs at which certain conditions must be met. A terminal-pair is an associated pair of accessible terminals such as an input pair, an output pair, and the like . In this case, the terminal-pair is the conductor and its shield of a coaxial connection. The four-terminal-pair standard is defined by the ratio of the open circuit voltage V at terminal-pair 2 to the current I at terminal-pair 4 (Iin = Iout at pair 4) when the current at terminal-pair 2 is zero and both the voltage and current at terminal-pair 3 are zero. This creates a well-defined standard which can be moved between different bridges and still give the same value.

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