Alexei Volkov
Romex, or NM, wiring is a type of non-metallic cable commonly used in electrical work. When working with Romex wiring, it is important to secure the cable to electrical boxes to protect the wiring connections and prevent damage to the cable sheathing. While metal electrical boxes are often considered stronger and more secure, plastic electrical boxes are also commonly used with Romex wiring. This introduction will discuss how to secure Romex wiring in a plastic box, including the use of clamps, connectors, and other methods to ensure a safe and secure installation.
| Characteristics | Values |
|---|---|
| Cable type | Nonmetallic (NM) or Romex |
| Cable clamps | Required for two-gang and bigger boxes; can be plastic tabs or NM clamps |
| Grounding | Metal-sheathed wiring requires bonding with a metal electrical box for grounding; NM cables require internal bare copper wire to be attached to a screw inside the box |
| Box material | Metal boxes are stronger, fireproof, and more secure than plastic boxes; plastic boxes are easier for DIYers to work with |
| Box attachment | Metal boxes provide stronger attachment to studs with screws; plastic boxes come with pre-attached nails for nailing into studs |
| Knockout holes | Metal boxes have knockouts that require removal and supplementary clamps; plastic boxes have built-in spring tabs that secure the cable |
| Cable length | At least 6 inches of free wire should extend into the box; 8-10 inches is better |
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What You'll Learn
Plastic boxes with built-in spring tabs
It is important to note that the spring tabs should not be punched out entirely. Instead, the Romex cable should be pulled and pushed through the tabs, allowing them to spring back and hold the wire in place. This prevents the cable from being pulled back out. If the tabs are punched out completely, they may become loose or separate, reducing their effectiveness.
Some plastic boxes, such as the Carlons brand, have plastic tabs that you push the cable past as it enters the box. These tabs then spring back and grab the cable. However, it is important to handle these tabs with care, as they can be fragile and prone to breaking. Leaving the tabs intact is crucial to maintaining the integrity of the wiring installation.
When working with plastic boxes, it is recommended to follow code requirements for securing the cable. For example, the National Electrical Code specifies that the cable should be fastened to a stud within a certain distance of the box, typically within 8 inches if there is no clamp and within 12 inches if a box clamp is used. This ensures that the cable is securely held in place.
While plastic boxes with built-in spring tabs offer a convenient way to secure Romex cable, some professionals still prefer metal boxes for their perceived higher quality and solidity. Metal boxes typically require additional clamping methods, such as removing knockouts and using cable clamps, to secure the cable. However, the choice between plastic and metal boxes ultimately depends on personal preference and the specific requirements of the electrical project.
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Plastic push-in connectors
One version of the plastic push-in connector includes a small gate piece that slides down into a slot and is then clamped down with pliers to secure the cable. Another type of plastic push-in connector is the plastic tab, which the cable is pushed past as it goes into the box, and the tab then springs back to grab the cable.
Some plastic boxes have built-in spring tabs that secure the cable as it is pushed into the box. These tabs are designed to be pushed in and pulled out, leaving them in place to prevent the cable from being pulled out.
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Plastic box clamps
Most plastic boxes have built-in spring tabs that secure the cable as it is pushed into the box. These tabs act as clamps to hold the cable securely in place. It is important to note that the cable clamp should not directly contact the wires themselves but rather the outer cable sheathing. This ensures that the clamp does not compress and damage the insulation around the individual wire conductors.
Some brands of plastic boxes, such as Arlington fiberglass boxes, have unique designs that secure the cable. For example, the Arlington box features a plastic insert that makes the cable bend sharply as it enters the box, providing a secure connection.
For larger boxes, cable clamps are typically required. Carlon and some other brands use plastic tabs that the cable is pushed past as it enters the box. These tabs then spring back and grab the cable, providing a secure hold.
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Plastic vs metal boxes
Plastic electrical boxes, typically made from PVC, have become increasingly popular, especially for residential wiring. They are lightweight, affordable, and much easier to install than metal boxes. They are also fire-rated. Plastic boxes are typically used for Romex construction, with non-metallic (NM) cable. Most plastic boxes have built-in spring tabs that secure the cable as it's pushed into the box.
Metal electrical boxes, on the other hand, have been the industry standard for years due to their strength, durability, and fire resistance. Metal boxes are made from steel or aluminium and are often recommended for commercial projects, although they are also used in residential settings under certain circumstances. Metal boxes are very strong and virtually impossible to bend, warp, twist, or crush. They are also more suitable for exposed applications, such as unfinished basements, garages, or outdoor areas, where they can withstand the elements and mechanical stress. Metal boxes are also required when using metal-sheathed cable (also called BX cable) or metal conduit, as the metal box is needed for proper grounding.
When it comes to securing Romex in a plastic box, it is important to note that the cable must be secured to the box at the point where the cable enters to protect the wiring connections and prevent damage to the sheathing. While most plastic boxes have built-in spring tabs, some also have plastic tabs that you push the cable past, which then spring back and grab the cable. There are also plastic push-in connectors that snap into the knockout hole in the box, with the cable inserted through and secured with a spring tab or other devices.
In some cases, clamps may be required for plastic boxes, especially for two-gang and bigger boxes. Cable clamps can be purchased separately, although some boxes come with pre-attached clamps. It is important to ensure that the cable is held securely and that the clamp does not compress and damage the insulation around the individual wire conductors.
Overall, the choice between plastic and metal boxes depends on the specific requirements of the project, including the type of wiring, installation environment, and cost considerations.
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Grounding Romex in plastic boxes
Use a Ground Clip:
An approved method is to use a ground clip, which slides onto the edge of a metal box. This anchors the equipment-grounding conductor tightly against the metal. However, this method is not suitable for plastic boxes.
Connect to Devices:
While plastic boxes themselves cannot be grounded like metal boxes, it is essential to bring the equipment-grounding conductor into the enclosure to ground devices such as switches and receptacles. Connect the bare or green wire directly to the green screw on the device.
Use a Green Grounding Screw:
For metal boxes, a green grounding screw is typically inserted into the threaded hole in the back of the box. The equipment-grounding wires are then connected to this screw, integrating the metal box into the grounding system. However, this method may not be applicable to plastic boxes.
Special Precautions for Romex or NM Wiring:
When using Romex or NM wiring with plastic boxes, special precautions must be taken to ensure proper grounding. Unlike metal-sheathed wiring, which depends on bonding with a metal box for grounding, Romex or NM wiring requires additional grounding measures to prevent a severed ground, which can be highly dangerous.
Clamping Methods:
To secure Romex or NM cable in a plastic box, clamping methods are often used. Some plastic boxes have built-in spring tabs that secure the cable as it is pushed into the box. Other boxes feature plastic tabs that the cable is pushed past, which then spring back to grab the cable. It is important to note that these tabs should not be punched out entirely; instead, the cable should be pulled through while leaving the tab in place to prevent the cable from being pulled out.
When working with plastic boxes and Romex or NM cable, it is crucial to follow electrical codes and guidelines to ensure proper grounding and safety.
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Frequently asked questions
Most plastic boxes have built-in spring tabs that secure the cable as it's pushed into the box. You can also use a plastic electrical box clamp or a plastic push-in connector.
It is recommended but not required. Romex wiring can be used with metal electrical boxes by attaching the bare or green grounding wire to the box with a screw.
Plastic boxes are inexpensive and easy for DIY home remodelers to work with. They come with pre-attached nails for nailing into studs.
Plastic boxes are weaker than metal boxes and may not resist damage as well. They are also not suitable for use in an attic unless your local electrical code permits it.
