How to Properly Use a Terminal Block

Three green terminal blocks against a white background.
  • 1 hours
  • Beginner
  • 35
What You'll Need
Wire strippers
Terminal block

A terminal block is one method of connecting a selection of different electrical wires. They come in a variety of shapes and sizes so you can normally find one that will be compatible with whatever project you are carrying out. However, the difference between blocks can lead to problems if an incorrect type is used or if it is not connected properly. Follow the advice below so you never have to worry about encountering these issues.

Step 1 - Terminal Block Type

Look at the electrical equipment you are working on to see what type of connection it requires; normally you will have either a screw-in or plug-in connection. Screw-in wires are placed inside the terminal block and screwed into position, and they are most common for equipment that does not require high voltage protection. A variation on the screw-in connection is one held in place by a spring mechanism. This connector can reduce the time spent on the job because you simply clip it into place instead of removing and replacing the screw.

A plug-in connection has a male terminal at the end of the wire. This terminal is connected to the female port on the terminal block and forms a secure connection. Plug-in blocks are commonly used in the fuse boxes of automobiles.

Step 2 - Choose Terminal Block

Once you know the type of connection that is required, you need to find a terminal block that fits the rest of your requirements. Consider what space you have for the connection and how many wires need to be connected. Terminal blocks are supplied in a variety of shapes and sizes, so you should be able to find one that suits your needs.

Next, choose the correct rating. Three, five, 15, or 30 Amp terminal blocks are widely available, and you'll want to buy the one that meets the highest current level it will conduct in order to allow the most powerful piece of equipment to function.

Step 3 - Secure Screw-in Connection

Always make sure that any electrical equipment is turned off before beginning work. For a screw-in connection, you will need to strip a small amount of the insulation from the end of the wire. Normally, around 1/2 inch is sufficient but this will depend on the component. Unscrew the retaining screw from the terminal block then insert the wire into the hole. Tighten the screw into place. Make sure it is fully tightened because if the wire is left loose, it will begin to heat up and melt the insulation. Over time, this could result in a fire so take a little extra time to make sure it is secure.

Step 4 - Secure Plug-in Connection

Position the terminal block and run the electrical wires to it, connecting the male terminal to the female port. Press firmly to ensure the connection is secure and won't come loose in the event of any subsequent movement.

Step 5 - Test Equipment

Once you have made all the connections to the terminal block, test your equipment to make sure it works correctly. Afterward, check the terminal block and the connections to make sure there is no excessive heat build-up and the wires are still securely in place.