Avid DIYer or not, most people have dealt at one time or another with installing a new light fixture, a dimmer switch, a movement sensor, and for the more involved, installing a light switch or maybe a fan switch activated by virtual assistance technology.
In any such cases, electrical devices that come with 3 or more wires attached are complemented with instructions and wire nuts to complete the installation and make all the necessary connections. The wire nuts supplied, however, are usually a cheaper version of the twist-on cone-shaped wire nuts.
Twist-On Connectors or Marrettes
Also known as wire nuts, cone connectors, thimble connectors, or in Canada, as Marrettes (named after its inventors regardless of the product’s brand), the twist-on connectors are widely used in North America and several European countries in residential, commercial as well as industrial wiring (Figures 1, 3, and 4).
Their means of connection is a tapered metal coil inserted inside a conical plastic insulated casing (Figure 2).
By twisting such a connector onto the stripped ends of two or more wires, the metal coil threads itself around the stripped wire ends drawing them together and squeezing them together tightly to make a positive and direct electrical connection.
They can however be easily undone by untwisting or turning counterclockwise to allow easy removal for future wiring modifications.
Some of those connectors are serrated with external grooves to provide a non-slip twisting torque (Figure 1), while on others the casings are molded in a hexagon shape (Figure 3) for optional use with a special tightening tool when doing larger jobs requiring a lot of the repetitive twisting movement, thus reducing wrist and arm fatigue.
Another special model made for use with heavier gauge wires is the twist-on connector molded with two wings (Figure 4), so that they can be twisted on as a wing nut with the ability to provide the motion with more torque while tightening it by hand.
Specialty Twist-On Connectors
There are some twist-on connectors with a ceramic casing instead of plastic, designed to sustain high-temperature applications. They offer a better solution when used for connections inside heating appliances.
There are also some specially designed twist-on connectors offering an additional connection at the top of the insulated cone-shaped casing. They can come as a special push-in connection through an opening at the top of the connector to allow for a single-conductor bare wire to be pushed in and secured, such as a ground wire.
A similar connector with a permanently attached “pig-tailed” wire protruding from the top is also available and offers the same benefits as the push-in connector. While one type is usually referred to as “screw-on grounding connectors” and color-coded green, another also comes color-coded white for splicing “neutral” wires while providing an extra wire for a pigtail connection to a device such as a receptacle’s neutral terminal.
3. Water Resistant
The common twist-on connectors don’t rate as water or moisture resistant and consequently shouldn’t be used for exterior or underground use.
Extra protection can be added with heat shrink tubing, resin packs, and possibly tape, but careful considerations should be taken before opting for such resolve, as a weatherproof twist-on connector pre-filled with a silicone-based sealant can provide extra protection against moisture and corrosion, providing a safe and durable connection in harsh environments.
4. Conductive Gel
Although twist-on connectors are not recommended for use with aluminum wires in the United States, the type containing a conductive gel is approved for use on residential aluminum wiring in Canada, even when copper wiring is combined with aluminum wiring.
Ease of Application
Those twist-on connectors or Marrettes are typically installed by hand and easy for a non-professional to do while requiring no more than a wire stripper or utility knife to perform a splice. They’re usually color-coded by the size and capacity of wires they can accept in multiple sizes and numbers.
They’re usually not used for wires larger than AWG #10 because of the wire’s rigid and inflexible properties making it practically impossible to achieve a positive, reliable, and solid connection, where crimp connectors, set-screw connectors, or other special clamping devices can offer a much more secure connection on wiring designed for such large current carrying capabilities.
Installing Twist-On Connectors
1. Plan Scale
The first thing to do is take into consideration the extent of your project and what it involves—the sizes of the wires you’re working with, how many wires will be inside each connector if the installation is going to be submitted to humid or corrosive environments.
You can subsequently determine if ordinary connectors or weatherproof are required (no sense in increasing the cost if there’s no need), how many connectors for each cluster size you have, and from there determine how many of each size or of which color-coded connector you have to get.
2. Turn Off Circuit Breaker
With your connectors on hand, a pair of long-nose pliers, and a wire stripper handy you can proceed to locate the circuit breaker assigned to that particular circuit and switch it off.
3. Open Terminal Box
You can now go to your terminal box and consider what is to be done. If it concerns a brand new installation with all new wires or an older installation onto which you’re adding a new branch, a fixture, or a switch, look at what you have in the box with all the wires in and how they will be regrouped in clusters.
If you're installing a new fixture, a switch, or an outlet, you might want to add jumper wires to properly connect them to the circuit, thus adding to each cluster of wires.
4. Check Wire Ends
Check the end of your wires to make sure their insulation is stripped to a proper length as instructed by the manufacturer or if that’s not available, the standard recommendation is to remove 1/2 to 5/8 of an inch (12 to 15 mm) of insulation—just keep in mind that this can vary.
Note: When splicing a stranded wire with a solid wire, it’s always better to strip the stranded wire longer than the solid by about 1/8-inch (3 mm) to enable you to hold the stranded wire so that it extends past the solid wire by that same length.
This compensates for the more flexible and soft stranded wire’s tendency to wrap around the solid wire as you turn the wire nut.
5. Clean Wires
Make sure all the wire endings are straight and clean, especially when redoing older jobs where the wires could be twisted or corroded or both.
6. Line Up Wires
Place all the wires for the same connection parallel and pointing in the same direction making sure they make even contact. All the ends of the solid wires should come up in perfect alignment with the stranded wire’s end protruding 1/8-inch (3 mm).
7. Insert and Twist
Holding the wires firmly so that they don’t move position, insert them firmly inside the wire nut and start turning the twist-on connector clockwise to begin the screwing action of the spiral insert threading its way in as it pulls in the wires.
As it moves forward onto the wires it gradually applies an increasing squeeze as the wire nut is torqued in by hand until it is very tight and the bare wire ends are all concealed inside the connector.
8. Test Connection
The last step is one of the most important and consists of testing the solidity of your joint by tugging on each wire to try and find or pull out a loose one from the connector. If any wire is not or doesn’t feel perfectly secure, the connection should be undone and started over.
It is important to note, though, that there are many different types of wire connectors. Some crimp-on, while others are simply slide-in or push-on, and lever types. It is therefore advisable to do some inquiring while choosing the right connector for specific projects.