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Grounding screws are often color-coded green and, when used on consumer electronics, often have a washer with gripping "teeth", to ensure better connections. Spring clamp terminals use a spring-operated clamping mechanism to hold the conductor in place. A screwdriver is inserted into the terminal, the wire is inserted and when the clamp is released it holds the wire in place. These types of terminals are very secure and ideal in environments subject to high vibration. Push-in connection This is simply a metal tube (sometimes insulated) in which you place the stripped end of one wire in one end of the tube, crimp it, and repeat for the other wire on the other side. Bullet connectors Figure 3: A spade terminal. The color of the insulation indicates the wire gauge to be used. There are many variations of insulation, from none to completely covered. There are also many manufacturers. This is a Panduit DNF18-250-M. (Source: Digi-Key online catalog) This article does not cite any sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.
I also quite like the single ended screw connectors that are a cross between eurostrip and wire nuts: Depending on the voltage and the current, there are standards that govern these connections. These standards are there for a reason, and you ignore them at your peril — sometimes in unexpected ways. For example, a friend had pot lights installed by some contractor at the lowest price. An insurance claim for an unrelated fire was rejected by the insurance company because the pot light installation was not to code. Bearing all of this in mind… In-line connectors They come in 2 and 3 pin versions. 2 pin connectors must not be used on 3 core appliances. There are also a few different pin configurations that have seen popular use over the years, so not all connectors are compatible with others. Many such connectors are only rated at 5A, a 5A connector is good for a 1kW motor. Let me make a disclosure here: I once worked for a large German connector company, and my current employer is a spin-off that maintains close “connections” with said company. I documented tidbits that I gleaned on connectors working on several projects in the industrial sphere over the years in two blogs: “ Which PCB Connectors Are Best?” and “ Unusual connectors.” The point is that this kind of exposure may possibly limit my knowledge as to all of the different ways there are to connect two (or more) ends of wire. Based on this, I hope that other members of the EEWeb Community will add their suggestions in the comments below. Soldered joints are permitted in both accessible and inaccessible locations. Practically you need to provide some sort of strain relief for the joint, as solder is very weak. The cable ends should always be twisted together before soldering, otherwise even very small movements during assembly can cause the bond to fracture. Twist at least a couple of full turns, otherwise some movement can still occur, and the joint break.
Types of Terminal Blocks
The main weakness of these is that they can sometimes loosen in time, creating a fire risk. This makes them forbidden for inaccessible locations, such as under tiling etc. Also many screw connectors are found that haven't been tightened up enough, creating reliability and fire risks. (Connector failure due to overtightening is far less common.)
As an aside (pun intended, as you will see), sometimes you just want to tap onto an existing wire. I suppose that you could cut the wire and make a three-way connection. Also, I have to admit to the very inelegant practice of whittling away a small segment of insulation on the wire and wrapping/soldering the tap. But there is a much better way, termed a wire-splice connector (Figure 7). Flex ends need twisting and folding over before use, and should not go in the same hole as cable, or the flex connection can be weak and electrically inadequate. Lone cables going into a connector terminal are bent double to ensure good grip. You take the two stripped ends of wire, insert them into the cone, and twist.The wire nut will, in fact, allow grossly mismatched wire gauge, a mix of solid-core and multi-strand wire, and allow you to join two, three, or even four wires. Provided that the bared portions of the wires are within the insulated cone, there is complete isolation. However, the joint itself is not very strong and tugging can cause it to come apart, which means that you should consider if mechanical stress is likely to occur in your application. On the plus side, it can also be unscrewed to allow for modifications. This connector has two channels. You slide the main wire along one channel and the tap (unstripped) into the second channel and close the assembly. It may require a pair of pliers to force a metal blade through the insulation of both wires (this technique is known as insulation displacement technology, or IDT) that remains in position, shorting the cables together. Butt-splice connectors with IDTJust because you can connect two wires together, it doesn’t mean that you should, but if you need to, then here’s how. There is a very cheap version of the wire nut that uses a small metal helmet instead of the insulator conical form. You insert the wires and then crimp them all together. However, I have been unable to tease an example out of the Digi-Key ether. Spade terminals Crimped flex ends can be safely used in mains plugs and other screw connectors. Ideally the flex should be twisted before the bootlace ferrule is applied, to avoid concentrating stresses on a small number of strands. The aforementioned butt-splice connection is forever. However, there is a cross between the butt-splice and flying blade approaches that is often referred to as a “bullet” connection (Figure 6). Choosing the right type of connector for your application, you should consider current requirements, voltage requirements, wire being used, mechanical strength and the environment.
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