As electricians, one of our most common tasks is to pull and terminate wires (conductors) from a source of power to a piece of equipment or device to utilize it. While for many circumstances we can accomplish this task as an uninterrupted wire run from breaker to outlet, there are many instances where we will need to make splices in those cables. At those joints, we are required to join the cables in some fashion to make them electrically continuous — or in other words, as if the wire wasn’t spliced.
Originally, when electricity was in its infancy, this was accomplished several ways. You could install the wires, clean and twist them together, dip them into molten solder, wait for them to cool, then tape up the joint. However, this was a time consuming and reasonably dangerous operation. There had to be a way to keep the molten solder just that — molten. That required a constant source of heat, which risked catching surrounding items on fire. The molten solder itself was a risk as well; an electrician could potentially spill an open pot or container of it on themselves or someone else, which would result in some pretty wicked burns. In addition to the risk of injury, it was not very practical to have to carry a pot of molten metal up into an attic or somewhere to attempt to make a splice in a box with several splices in it already! Another method (which still can be seen today, although rarely) would be to use a crimped ferrule to hold the splice together, and then tape the joint or install some type of insulated cover over it.
So in the early 1930s, patents were issued for something we would consider today to be a wire nut. The concept for all pressure-type wire nuts is reasonably similar. Two or more wires are stripped and then a wire nut is twisted on all of them together, making the joint electrically continuous and providing an insulating cap on the end of said joint. This means that it won’t short against ground or the conductor next to it, and the electrician (or anyone touching the joint really) is protected from being shocked. Another added benefit to the wire nut is that they can be reusable, to a point. So if an additional conductor needs to be added or if something needs to be rewired, the connector doesn’t need to be cut off and disposed of. It can be reused, provided it is of a size large enough to accommodate the new splice being made.
Following are the current 2020 NEC articles pertaining to wire splicing, and summaries of the information contained within them.
110.14 Electrical Connections.
110.14(B) “Splices. Conductors shall be spliced or joined with splicing devices identified for the use or by brazing, welding, or soldering with a fusible metal or alloy. Soldered splices shall first be spliced or joined so as to be mechanically and electrically secure without solder and then be soldered. All splices and joints and the free ends of conductors shall be covered with an insulation equivalent to that of the conductors or with an identified insulating device.
“Wire connectors or splicing means installed on conductors for direct burial shall be listed for such use.”
110.14(C)(2) “Separate Connector Provisions. Separately installed pressure connectors shall be used with conductors at the ampacities not exceeding the ampacity at the listed and identified temperature rating of the connector.”
300.13 Mechanical and Electrical Continuity — Conductors.
300.13(A) “Conductors in raceways shall be continuous between outlets, boxes, devices, and so forth. There shall be no splice or tap within a raceway unless permitted by 300.15, 368.56(A), 376.56, 378.56, 384.56, 386.56, 388.56 or 390.56.”
300.15 Boxes, Conduit Bodies, or Fittings — Where Required. In summary, this article says that you shall have a box at all splice points.
376.56 Metal Wireways: Splices, Taps & Power Distribution Blocks. In summary, this article states that you can make splices within a wireway, provided they are accessible and do not exceed 75% fill at that point.
378.56 Nonmetallic Wireways: Splices and Taps. In summary, this article states that you can make splices within a wireway, provided they are accessible and do not exceed 75% fill at that point.
384.56 Strut-Type Channel Raceway: Splices and Taps. In summary, this article states that you can make splices within a strut-type channel raceway, provided the raceway has a removable cover, it doesn’t exceed 75% fill at that point and the splices are made by approved methods.
386.56 Surface Metal Raceways: Splices and Taps. In summary, this article states that you can make splices within a surface metal raceway, provided the raceway has a removable cover accessible after installation, it doesn’t exceed 75% fill at that point and the splices are made by approved methods.
388.56 Surface Nonmetallic Raceways: Splices and Taps. In summary, this article states that you can make splices within a surface nonmetallic raceway, provided the raceway has a removable cover accessible after installation, it doesn’t exceed 75% fill at that point and the splices are made by approved methods.
390.56 Underfloor Raceways: Splices and Taps. For underfloor raceways, you may only make splices in junction boxes. There is an exception for trench-type flush raceways — you may make splices provided that the raceway has a removable cover accessible after installation and that it doesn’t exceed 75% fill at that point.
392.56 Cable Trays: Splices and Taps. In summary, you may make splices within cable trays provided they are made and insulated by approved methods and they are accessible. In addition, where not subject to physical damage, those splices are permitted to project above the side rails.
Today, there are many different manufacturers of the wire nut. While the number of wire nut manufacturers is almost endless, some of the bigger manufacturers are 3M, Ideal, and Buchanan to name a few.
As with anything, we are required to follow the manufacturer’s instructions on how to use their individual products. However, the process of installing a wire nut is pretty much the same from manufacturer to manufacturer. Strip approximately three quarters of an inch from the end of the wires you want to terminate (the actual length will vary according to the size of the wire nut, the number of wires, etc). Place the wires together by holding them between your fingers, making sure that the stripped ends are all even at the end. Place the wire nut onto the exposed end of the stripped wires and twist, making sure that all of the conductors are being twisted together for a few turns under the wire nut. It’s preferable to give the conductors a final tug to ensure that they were all captured in the joint.
There are a few different general types of wire nuts available. The standard wire nut is usable in most indoor applications where you are trying to splice two or more wires together. If you are in an outdoor environment (or an environment where condensation may be an issue — say, on the exterior of a commercial freezer or refrigerator) you will want to use below-grade wire nuts for your splices. These connectors are filled with some type of water repelling/anti oxidizing compound (like a type of silicone) that staves off the effects of moisture. For high temperature applications, there are ceramic wire nuts. These operate the same as a standard wire nut, but instead of the plastic cap it has a ceramic one which won’t melt in the heat being generated by the connected equipment. For grounding purposes in residential applications, there are a couple different flavors available. The first one looks just like a standard wire nut, but has a small hole opposite the open end. This is designed for one of those grounding wires to be left longer than the others. That conductor passes through the hole and after you twist like normal, it leaves you with a single grounding conductor to attach to your device. Another variant of this is the pigtail wire nut. It has a built-in wire tail opposite the open end. Once you spin your joint, it leaves you a pigtail to attach to your device.
Lastly, there are push-in type wire connectors. A standard wire nut requires you to twist your wires together to get connection, whereas the push-in types allow you to just push the wires into the connector. A spring-type metal bar holds them together to form the electrically continuous joint. They are sized by both the amperage of the joint as well as the number of wires. So for example, a two-port, 20 amp connector will hold two 12-AWG conductors. In addition, relatively new to the market are lever-lock-type wire connectors. They operate much the same as a standard push-in type wire connector, but instead of using force to push the stripped end into the metal pressure connector, it is lever operated. Simply put the stripped ends into the wire connector and pull down the lever, and they’re held in place. The good thing about these is that they make it easy to remove a wire — simply pull up on the lever, and your wires will pull right out. But as with most things that we use for efficiency, this type of wire connector is definitely more expensive than a standard wire nut.
Wire nuts are sized according to the number and size of wires they are intended to connect. Most manufacturers use the following coloring protocol: gray is the smallest, ranging between 16-22 AWG. Blue is the next largest, at 14-22 AWG. Orange is 14-18 AWG. Yellow connectors can splice between 10 AWG and 18 AWG, and red wire connectors the same. There are some available above red wire connectors, but these will vary from manufacturer to manufacturer. As for the number of wires allowed into any given wire connector, as well as the sizes, make sure to consult the wire connectors’ packaging. It is important to remember that just because one manufacturer allows two or three of one size wire in a particular wire nut, it doesn’t necessarily mean that other manufacturers will.
Wire connectors range in price from a few pennies each for the smaller ones to a dime or so for some of the larger wire connectors. Specialty wire connectors (like the underground or high temperature ones) will easily go above that per unit. Pricing is very broad and will vary from manufacturer to manufacturer. In addition, typically, the more you buy at once, the cheaper per unit the price will be.
In summary, we are required to use a wire splicing method and materials that are approved and rated for the purpose we are trying to serve. With so many variants of the wire connector available to us, there is bound to be one out there for the application that you face.