How Do You Connect Wires to Terminal Blocks?

Wiring terminals on a terminal block appears easy, however getting it right is important when it comes down to wiring Terminal Blocks properly. A loose connection between terminals or not having the appropriate connectors for your application will result in intermittent connections to ground causing potential overheating of the equipment, as well as problems with signal transmission, potentially creating issues that could cause your equipment to fail completely. The advantage when wiring Terminal Blocks correctly is you can create a more dependable connection once you know the basics of how to wire Terminal Blocks, making wiring easier!

Control panels, power supplies, and automation equipment use terminal blocks. You will find these types of products (and a multitude of others) when you look for a pcb connector. This guide has been prepared to assist you in making the right decision when comparing terminal blocks with common Wire-To-Board Connectors such asmolex connectors or JST connectors.

What Is a Terminal Block?

An electric terminal block is a connecting device to combine electrical wires in an organized way without any danger of shock. Terminal Blocks feature insulated plastic outer casings and are typically composed of a metal element on the inside that holds the wires securely in place, allowing electricity or signals to flow through both of the connections present within each terminal block.

You can have a cleaner and more serviceable connection using a terminal block compared to twisting or permanently soldering wires. If you need to replace the wire, check a circuit, or perform maintenance on your equipment at some point in time, you should be able to easily disconnect that particular piece of wire from the entire assembly without having to destroy the entire assembly.

This is the reason terminal blocks are found at a high frequency in industrial control cabinets, machinery, power modules, lighting systems, and on Printed Circuit Boards.

How Do You Connect Wires to Terminal Blocks?

When it comes to connecting your wires to a terminal block, you must start with the appropriate terminal block and move on to stripping, inserting, tightening/clamping, and verifying that the connection is secure. All five steps are important; if you make an error during any of these steps, it could result in a poor-quality (weak) connection.

Step 1: Choose the Right Terminal Block

Before connecting wires to Terminal Blocks, ensure that they are appropriate for your application by checking the following attributes: Voltage Rating (V), Current Rating (A), Wire Size Range, Number of Positions on the Terminal Block, Pitch (or Size), Temperature Rating (C°), and Mounting Style.

An example of this is that a small signal wire will require a different kind of connector than a high-current power wire. Additionally, terminal block connectors on a printed circuit board (PCB) will have different connector requirements than the same type of connectors on a din rail mounted inside an electrical enclosures.

A WTB wire terminal or connector WTB is likely a more appropriate method of connecting a cable harness to a PCB than using a government or normal style terminal strip. Many engineers and purchasers are comparing parts from various competitors including Molex, JST, TE Connectivity, Phoenix Contact, and the numerous compatible connector manufacturers to determine the most economical option based on product availability and design criteria.

Step 2: Turn Off the Power

Before starting to work on wires, it is essential to turn off the power. It might seem obvious at first glance, but this is one of the most critical aspects of safety. Utilize an appropriate tester after turning off the power to verify that the circuit has no voltage present.

This is critical for control panels, power supplies, wires in buildings and other types of equipment that have very high current draw. A low voltage DC systems can cause damage to componentry just from the wires accidentally connecting to the wrong terminal.

Step 3: Strip the Wire Properly

Use the correct tool for the job when stripping wire insulation (i.e., a wire stripping tool), and only strip off as much insulation from the end of the wire as necessary to make the connection. Do not strip off too little insulation (unfitting). Do not strip off too much insulation (excessive).

It's important to trim the wire ends so that they are appropriate for the terminal block. This will help ensure that you have good connection within the terminal while at the same time not having exposed bare copper on the outside of the terminal block. Exposed bare copper could create short circuit problems.

Although there are many types and brands of terminal blocks, many of them require a strip length between 5 and 10mm. It is important to find out the proper strip length; the best way is to check the datasheet or the labeling on the connector body when available.

Step 4: Use Ferrules for Stranded Wire When Needed

Ferrules are small metal sleeves, which fit on the stripped ends of stranded wire, to provide a cleaner connection and give better mechanical strength to the overall electrical connection. The ferrule is placed over the stranded wire prior to terminating onto the electrical terminal.

Ferrules will prevent individual strands from fraying and provide a better, more firm connection to the terminal. In addition to these benefits, ferrules can be helpful for minimizing loose copper strands, ensuring you have a proper connection, and providing a solid surface for connecting/disconnecting wires at screw terminal blocks in industry control wiring applications.

While certain spring and push-in terminal blocks can take in stranded wires directly, letting them connect to a facility might help create a clean and more reliable connection with ferrules.

Step 5: Insert the Wire Fully

Insert the stripped conductor completely into the terminal by inserting the metal conductor into the clamping area and verifying that the insulation is not pinched between the clamp and the terminal.

When covering the insulation rather than the copper conductor, it will appear to be an acceptable connection, yet fail once current is delivered through them. When using a wire that is too short for this application, the wire may come loose or create intermittent faults after repeated usage.

Whenever you are connecting a PCB connector or pluggable terminal block, please verify that the polarity and terminal number are correct prior to applying power to the circuit. If they are connected in reverse, it may destroy your electronic parts.

Step 6: Tighten, Clamp, or Lock the Wire

There are different types of terminals used to hold wires in place. A screw terminal holds the wire using a screw to secure it. A spring clamp terminal holds the wire using a spring-loaded clamp. A push-in terminal allows you to insert both solid and ferruled stranded wires directly into the terminal. A pluggable terminal allows you to wire the plug first before connecting it to the PCB header.

It is important that you secure the screw terminals properly by making sure to neither over-tighten nor under-tighten them. A screw that is too loose may not be able to hold sufficient pressure on your conductor. Conversely, by using too much torque while tightening down your screw terminal, you may run the risk of damaging the head of your screw, collapsing your conductor or cracking your plastic housing.

As far as manufacturing tasks go, using a torque screwdriver is an excellent solution to having uniform connections for all assembly connections.

Step 7: Check the Connection

Once connected, gently pull the wire back to ensure it is secure. Look closely at the terminal to check that there's no loose strands, no exposed copper out of the protected area and that there is no damage to the insulation around the wire.

Testing for continuity and voltage drop and inspecting for excessive heat while under load, or performing vibration tests are common practices for critical pieces of equipment. This applies to industrial, automotive, and safety-related industries.

Common Types of Terminal Blocks

Terminal blocks come in different styles. Which type of terminal block is best for your application will be determined by how you plan to use it; how frequently you need to do maintenance on it; the amount of space available for installation; and how quickly you must assemble it.

Screw Terminal Blocks

The most popular type of terminal block is a screw terminal block. You insert the wire and use a screw to hold it in place. Common applications for screw terminals are power supply connections, control panels, alarm systems, and industrial equipment.

They're straightforward however! The biggest point is that the screws should be installed and tightened correctly, as failing to do so could result in a loss of ability for the unit to function properly. Be sure to perform a verification at the time of design and throughout your maintenance schedule if your installation is subject to high-vibration conditions.

Spring Clamp Terminal Blocks

Because spring clamps apply spring action against the wire, they are suitable for use in applications that vibrate since the constant pressure from the spring ensures the conductor stays secure within the terminal block connection.

They are commonly used in automation systems, rail machinery, control cabinets and many other situations where a dependable, long lasting product is needed.

Push-In Terminal Blocks

The push-in terminal block is great for making wiring simple and fast as all you need to do is push the solid conductor or ferrule terminated stranded conductor directly in. This feature may save time in production or when connecting numerous conductors together.

They are popular when speed, neat wiring, and repeatable assembly are important.

Plug Terminal Blocks

The two components of plug terminal blocks are a plug and the header mating to it. You can attach the cables onto a plug, then that plug will fit into the header on the PCB. As a result, it will be easier to install and maintain these types of connectors.

Plug terminal blocks are commonly found in LED drives; controllers; inverters; communications devices and power modules etc. Therefore, when comparing plug terminal blocks with wire-to-board connectors, people frequently compare both of them as they can both provide a means to connect wires to a printed circuit board.

Terminal Blocks vs. Wire-to-Board Connectors

Both of these devices can be used to connect wires onto a circuit board, but they may not serve the same function.

A terminal block is an excellent choice for installers who have to connect wires in an application where they can do the wiring in the field. Terminal blocks are easy to wire, easy to inspect, and easy to service, which is why they are popular in control panels and equipment that require maintenance.

Generally speaking, when connecting a pre-made cable assembly to an electronic device, a wire-to-board style of connector is preferred due to it being compact, tidy, and good for mass production. This type of connector is manufactured by several different companies although the two most popular would have to be the Molex and JST brands; these connectors can be found in virtually every type of consumer electronics, battery packs, smart devices, appliances, automotive modules, and industrial equipment.

If your product requires a detachable cable harness, a locking mechanism, and a compact PCB design, you might want to select a Molex®, JST® or equivalent manufacturer to supply a wire-to-board connector; if you need quick field wiring with a screwdriver, lever, or push-in terminal, a terminal block may be more practical.

How to Choose the Right Connector

It is important to select the correct connector based upon several factors other than simply physically fitting with the other end. You must also consider the end use of the connector.

Begin with determining the product's rated current and voltage ratings; then check all wire gauges; contact resistance; operating temperature; cable type; pitch; locking structure; mating cycles'; and by their standards; if an international product specifies that UL, IEC, RoHS, REACH or similar compliance documents are required.

Branding can also play an important role. Many buyers prefer to use trusted brands such as Molex or JST due to their consistent high level of quality, extensive product selection, and detailed technical information. That being said, a considerable number of buyers are also trying to find compatible products to lower their total costs or speed up their production timelines or to support their custom cable assembly projects.

When selecting an additional supplier, ensure that they are able to supply samples, drawings, test reports and consistently produce the same quality of product. A low cost will not benefit you if the connector fails in the end product.

Practical Tips for Better Wire Connections

Both a good connector and a proper installation will ensure proper connectivity. If a wire isn't properly prepared, or an incorrect-sized wire is used, even the highest quality terminal block could potentially fail.

• Use the correct wire gauge for the terminal block or connector.
• Follow the recommended strip length.
• Use the correct tightening torque for screw terminals.
• Use ferrules for stranded wire when recommended.
• Do not leave loose copper strands outside the terminal.
• Do not put insulation under the clamp.
• Check polarity before powering the circuit.
• Use locking connectors when vibration or movement is expected.

Before making bulk orders for production connectors, request for datasheets, samples, and test results. For custom wire harnesses, confirm the wire length, pinout, crimping standard, pull force requirement, and packaging method prior to ordering.

Common Mistakes to Avoid

A frequent error is using a connector with a capacity that does not match the current being supplied to it. If the current is too great, the connector could become excessively hot. Over time, this heat may degrade the connector housing, compromise the integrity of the contact points or present a safety hazard.

Another mistake is to cut wire incorrectly when stripping it. A lot of exposed copper wire is unsafe. Similarly, too little exposed copper can lead to poor electrical contact; for these reasons, it is essential to provide a clean and precise crop length when stripping wires because this alone will make a major difference in how your wiring will perform.

Sometimes people use stranded wires to connect to the terminal without checking that there are no loose strands of wire. A single loose strand may contact the next terminal and create a short circuit. This is one reason why ferrules are commonly recommended when using stranded wiring.

A connector purchased solely for its low price is a poor choice, even though cost is an important consideration. Reliability is more important when selecting a connector than the cost. A defective connector can result in costly returns, repair time, equipment failure, or customer dissatisfaction.

Where Molex and JST Fit in Wire Connection Solutions

A cable harness commonly connects wires to printed circuit boards (PCBs) using a soldered terminal, a plastic housing piece, and a setup header; however, there are alternative methods for connecting via a soldered connection. Examples of two other connectors that perform this function are JST and Molex.

JST connectors are widely found in battery packs, LED items, electronics, appliances, and small PCB assemblies. Molex has a significant selection of connector systems suitable for consumer products, industrial equipment, automotive applications, data devices, and power supplies.

When replacing a terminal block by using either a Molex or JST connector, you should not just measure the spacing between the pins (pitch) but also verify current capacity, wire size range, design of the pin locking mechanism and the maximum allowable height of mating pins, temperature ratings, and any applicable testing standards.

This is a place where a professional connector supplier can assist buyers. A professional connector supplier will provide recommendations for standard parts, alternative parts that work together, and custom cable assemblies using your actual application.

FAQ

Are splices legal in an electrical panel?

Most locations allow for splicing inside an electrical panel if the splice uses a connector that meets the requirements of the local governing electrical code, is installed properly, remains accessible and will comply with all local electrical codes/customs etc. However, there are differences from one area to another, both nationally and locally, regarding approval of splices and how to make them. For any building wiring or electrical panels always be sure you are following the proper code and having a qualified electrician do the work.

What are the three types of connectors?

The most common connector types include wire-to-wire (the connection of two cables or wires), wire-to-board (the attachment of wires directly to a printed circuit board), and board-to-board (the attachment of two circuit boards together). Another type of connector that can be used for wire connections is terminal blocks, which are often found in Industrial and field wiring applications.

Can you put two wires into one terminal block?

Terminal blocks can only be fitted with two wires if they are designed and rated for such applications. Most terminals are designed to be used with only one conductor. If you inject two conductors into a terminal that is not designed for it, one conductor may not be adequately clamped due to its weight causing it to become overheated or loose connections will occur which could result in failure. When distribution of power or signal is required, make use of a suitable distribution terminal, jumper, or multi-wire terminal block.

Do terminal blocks require ferrules?

Ferrules do not always need to be used with stranded wire, as they are primarily used to maintain a uniform size of the stranded wires, and therefore maximize the amount of contact area. Ferrules are also often used with screw terminals and in wiring that connects industrial equipment to each other. Some spring-clamp and push-in terminals may allow you to use stranded wire without attaching ferrules; however, you should always confirm that you are following the instructions from your connector manufacturer.

Is a terminal block better than a soldered connection?

The choice of connection type depends on the application. A soldered connection is solid, permanent and small; however, it is more difficult to service than a terminal block. Terminal blocks are easier to connect/disconnect, inspect, and replace, therefore if field serviceability is a concern, terminal blocks are normally more feasible than soldered connections or WTB connectors or crimp connectors for compact electronic devices.

When Should You Contact a Connector Supplier?

It is often wise to get in touch with your connector supplier early on before you decide between using a terminal block, connector (e.g., molex), connector (JST), or custom WTB solution so that you can solicit their expertise and avoid design changes later. It may also save you valuable development time by promoting good communication between parties.

A supplier is able to assist customers in verifying the current rating, pitch, wire size, mating direction and locking style of connectors as well as providing information on PCB dimensions, cable length and assembly type. If you need custom wire harnesses, unique pinouts, manufacturer specific alternatives or develop a replacement part that is more economical, providing drawings, pictures or sample components along with an electrical requisition will help to speed up the recommendation process.

While it is not hard to connect wires to terminal blocks, having quality wiring depends on doing the above-mentioned elements correctly. This includes: choosing the appropriate connector, stripping the wire correctly, inserting completely, clamping securely and inspecting the connection. Whether using a screw terminal block, a spring terminal, a pluggable terminal block, a Molex connector, a JST connector or a WTB wire connector, the end goal remains the same - to achieve a reliable and easily maintained electrical connection.