Terminals & Connectors

Today we will be taking a look at some of the different types of terminals and connectors commonly used in 12 volt electrical installations. Often overlooked, these are one of the most important items of your system as they allow you to transfer power from one cable to another, so making sure you have the correct one can save you time, money and problems in the long run. With so many types, styles and variations however, it can be difficult to determine what terminal you need. In this guide, we will walk you through the options to help you better understand this critical component in 12 volt electrical systems. 

Terminal or connector?

Firstly, let's understand the terminology. The terms 'terminal' and 'connector' are often used interchangeably, but we prefer to think of a terminal as something that fits to the end of a cable and enables that cable to be connected to a piece of equipment, whereas a connector is something that enables two cables to be joined together (i.e. it fits to the ends of two cables).

The different types of terminals and connectors

There are a number of different options when it comes to terminals and connectors and in this section we will explain the different types. Each type will have different characteristics that will make it best suited to specific applications, so you should consider carefully what's required of the connection what environment it will be used in. The table below shows the different types of terminals and connectors typically seen in cars, campervans, motorhomes, caravans, canal boats, yachts, off-grid & other 12 volt applications, together with an image and a brief description.

	Type of terminal / connector	Description
	Insulated terminals & connectors	Fitted with a hard PVC insulation, these terminals are colour coded to help with selecting the correct size to fit your cable.
	Non-insulated terminals & connectors	Typically made of brass, with or without a tin coating, these terminals have no insulation over them, enabling you to inspect the quality of the crimp before fitting a separate insulting sleeve or cover. Male and female blades are also available in 'locking' versions that have a small tab on the rear that latches them into place in relay sockets, connector blocks etc. and prevents them being pulled back out. Brass 'bullets' are crimped to the cable and then inserted into sleeved 'connectors' to join them together, using friction to hold them in place.
	Adhesive-lined heatshrink terminals & connectors	Fitted with an adhesive-lined, polyolefin heatshrink sleeving, these terminals create strong environmentally sealed connections that provide excellent cable strain relief. These are superior to standard pre-insulated terminals, making them the best choice when you need maximum protection for your electrical connections, particularly in harsh environments.
	Copper tube terminals and connectors.	Suitable for cables carrying large currents such as battery cables or power feeds. Made of pure copper with a tin plating to help prevent against corrosion.

The different styles of terminal ends

Although the characteristics of the terminal types differ, you will notice that the ends of them, i.e. the part that connects to a piece of equipment, are often common or standardised. This is essential so that you can connect different terminal types to the same piece of equipment. These standardised end connections come in the form of 'push-on' connections, that rely on friction between the connecting parts to hold the terminal in place, or 'bolt-on' connections, that rely on the terminal being clamped in place with a nut over a threaded stud, or with a screw.

Some terminal types are available with different styles of end connection whilst others are only available with one style. In the table below we show a range of end connection styles that are available, using our insulated terminal type as an example. 

	Style	Description
	Butt connector (aka in-line connector)	Used for permanently connecting one length of cable to another of the same gauge and often used to extend cable or splice in a new section. These connectors don't have an end-connection style as such, since they are just intended to join cables together and don't connect to any other equipment.
	Female blade terminal (aka 'half-insulated' terminal) Push on	Probably the most common style of end connector available, allowing you to connect to fuse boxes, switches, relays & other equipment fitted with matching male terminals. Can also be used with male blade terminals to join two lengths of cable together in applications where you need a removeable connection. These female blades are available in standardised widths of 2.8, 4.8, 6.3 and 9.5mm (these sizes are derived from imperial equivalents) and have insulation over the crimp section only.
	Male blade terminal - push on (aka 'spade' terminal) Push on	Can be used with female blade terminals to join cables together, or with piggyback terminals to create a shared power connection. These male blades come in standardised widths of 2.8, 4.8 & 6.3mm (these sizes are derived from imperial equivalents)
	Piggy-back terminal Push on	Used to create 3-way connections to provide power to two outputs, or to enable a 'splice' to take power off part way along a cable run.  Can be used in combination with female & male blade terminals. Normally only available in standardised 6.3mm width.
	Fully insulated female blade terminal Push on	As per the female blade terminal above, but with insulation extending over the connecting end to provide extra protection. These are available in standardised widths of  4.8, 6.3 and 9.5mm (these sizes are derived from imperial equivalents). Again, typically used on equipment or components fitted with matching male terminals.
	Male bullet terminal Push on	Typically used with the female version (see below) to make removeable connections when joining cable together. Bullet diameters are normally 4 or 5mm
	Female bullet terminal Push on	Typically used with the male version (see above) to make removeable connections when joining cable together.
	Fork terminal Bolt/screw on	Used to attach to screw or bolt connections such as those found on fuse boxes, busbars or battery terminal clamps. Available with a large range of fork widths from 3mm upwards.
	Ring terminal (aka eyelet terminal) Bolt/screw on	Used to attach to screw or bolt connections, offering a more complete and secure connection than fork terminals. Typically used for fuse boxes, busbars or battery terminal clamps. Available with a large range of hole diameters from 3mm upwards.

Fitment for different cable sizes

As well as catering for different connection end styles, terminals and connectors need to accommodate different cable sizes that you might need to fit them to. All the above terminals and connectors use crimping to secure the cable, which means that the part of the terminal surrounding the cable has force applied to it by a crimp tool to deform it, trapping the cable under pressure and ensuring good mechanical and electrical connections. But to ensure this is successful with different cable sizes the cable-end of the terminals needs to be slightly different depending on the cable size being used.

For insulated terminals and adhesive-lined heatshrink terminals, the colour of the insulating sleeve acts as a quick reference guide to identify what cable size range it suits, which is as follows:

• Red: 0.5-1.5 mm² cable
• Blue: 1.5-2.5 mm² cable
• Yellow: 3-6 mm² cable

For non-insulated terminals the fitment range is typically the same as for insulated terminals (i.e. 0.5-1.5mm², 1.5-2.5mm², 3-6mm²) but since there's no colour coding and the terminals are rarely marked it's difficult to work out what cable size a particular terminal suits just be looking at it. For this type of terminal, your retailer should indicate on the packaging what cable size they are to be used with.

Copper tube terminals are used with larger cable sizes and a particular terminal will generally only fit one cable size rather than a range (e.g. 10mm², 16mm², 25mm² etc.). The cable size and connecting hole diameter are normally stamped onto the the terminal and will be shown as 25-6, for example, which means it suits 25mm² cable and has a 6mm dia. connecting hole hole. This makes for easy identification.

What size should I pick?

So now you know how to choose the correct terminal based upon the cable size you want to use, how do you know what end connections type and size to pick? Well you simply need to measure the matching connector on the piece of equipment you're connecting to.  As we can see from above, blade, fork & ring terminals are available in various sizes of blade/fork width or ring diameter to suit most applications. If you are unsure, you can use calipers to measure the connection point on the equipment, for example the width of the matching blade or the diameter of the bolt.

If you're creating your own connection with, say, male and female blade terminals, or male and female bullet terminals, you would just need to make sure that both terminals have matching widths/diameters.

Should I crimp or solder?

We always recommend crimping for most applications, especially automotive, because solder can work-harden and crack over time when subject to vibrations experienced in vehicles. This can lead to poor electrical connection, increased electrical resistance and eventual failure of the solder joint. Soldering can be used where there is no alternative (e.g. the connection point is designed to be soldered) and it can sometimes be useful to solder in addition to crimping (e.g. for added mechanical strength and improved electrical conductivity), but in most cases crimping alone is perfectly adequate, as long as you use a good quality crimping tool.

To learn more about this you can read our crimping tool guide here

So how do I pick the best terminal for me?

From the above we can see that selecting the best terminal really comes down to two key considerations which are the size of cable you're crimping to and the style/size of the connection point on the piece of equipment you're connecting to. If you're creating a connection between two cables then it would be down to a choice between a permanent or removeable connection and the style of terminal (e.g. butt connector, blade, bullet). You might also want to consider factors such as whether you want to inspect the crimp, whether it needs to be protected from the environment etc. as these might influence your decision.

We hope you have found this article helpful. If you have any further questions please contact our support team. 

Disclaimer - The information contained in these articles is provided in good faith and we do our best to ensure that it is accurate and up to date, however, we cannot be held responsible for any damage or loss arising from the use or mis-use of this information or from any errors or omissions. The installer is ultimately responsible for the safety of the system so if you are in any doubt, please consult a qualified electrician.