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NM stands for non-metallic and refers to a type of electrical cable with a vinyl or PVC outer sheathing. It is the most popular type of wiring in homes and is used for nearly all residential electrical devices. NM cable is also known as Romex, which is a brand name for one type of NM wire. NM wire is lighter than metallic sheathed wiring and easier to unspool and straighten out. It is also cheaper and easier to install than metallic wiring.
| Characteristics | Values |
|---|---|
| Full form | Non-metallic sheathed electrical cable (in North America) |
| Other full forms | Noise margin, Never mind (internet slang), Namma Metro (Bangalore, India), Nao Sena Medal (Indian Navy) |
| Cable type | Non-metallic sheathed electrical cable |
| Cable composition | Two or more insulated conductors contained in a non-metallic sheath |
| Cable coating | Vinyl or thermoplastic |
| Cable colour | Colour-coded outer sheathing to identify wire gauge (white for 14-gauge, yellow for 12-gauge, orange for 10-gauge) |
| Cable insulation | Colour-coded PVC (polyvinyl chloride) |
| Cable usage | Residential electrical wiring, interior residential wiring, within ceiling cavities or walls |
| Cable compatibility | Cannot be used outdoors, underground, or in damp locations |
| Cable rating | 600-volt for exposed and concealed work in normally dry locations |
| Cable temperature rating | 60ºC (140ºF) for Type NM-B, 90ºC (194ºF) for NM-B with "B" suffix |
| Cable security | Secured at intervals not exceeding 4.5 feet and within 12 inches of junction boxes |
| Cable splicing | Allowed but must be done in a code-approved fashion, typically in an accessible electric junction box |
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What You'll Learn
NM cable is non-metallic sheathed electrical cable
NM stands for non-metallic sheathed electrical cable. NM cable, also known as Romex, is the most popular type of wiring in a home. It is used for nearly all residential electrical devices such as GFCI outlets, lights, and wall outlets. It is also used for commercial wiring, such as lighting and outlets in commercial structures.
NM cable is a type of electrical wire with an outermost sheathing made of PVC. The sheathing bundles individual wires into a cable. The wires are copper and are individually coated in plastic. The outer sheathing of NM cable is an extremely tough 30 mil-thick PVC jacket that serves to protect the bundle of individual wire conductors. The sheathing is also colour-coded to quickly identify the wire gauge of the cable. For example, the 14-gauge wires cable has white sheathing and is used for 15-amp circuits, while the 12-gauge wires cable has yellow sheathing and is used for 20-amp circuits.
NM cable is simple to cut with just a set of side-cutting pliers. Once cut, NM cable is easy to rip lengthwise since the sheathing is plastic, not metal. NM wire is also lighter than metallic sheathed wiring, making it easier to unspool and straighten out. It pulls easily through holes in studs because of its smooth sheathing. In the case of Romex, a coating is added that makes the sheathing even more slippery.
NM cable cannot be used in certain situations, such as outdoors or when wiring is exposed along the face of foundation walls. In these instances, the electrical code calls for conduit installations. NM cable also needs some sort of protection in certain applications or when not inside a wall. It is not suitable for outdoor use due to its lack of moisture resistance.
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Used for residential wiring of luminaries, devices and appliances
NM stands for non-metallic and refers to a type of electrical wiring cable with a vinyl or PVC outer sheathing. It is the most common type of wiring used in homes, particularly for residential electrical devices such as GFCI outlets, lights, and wall outlets.
NM cable is also known as Romex, which is the brand name of one type of NM wire made by the Southwire Company. Other brands of NM cable include Encore Wire and Tianjin Feiya Fengda Wire & Cable Technology Co., Ltd. NM cable comes in different forms depending on its intended use. Standard NM cable, also known as NM-8, is suitable for interior residential wiring within ceiling cavities or walls. It is approved for use only in dry areas and cannot be used outdoors or buried underground.
Type NM-B, a non-metallic sheathed cable, is commonly used for residential wiring of luminaries, devices, and appliances. It is rated for 600 volts and can be used in both exposed and concealed work in normally dry locations. NM-B cable may be installed in air voids and joints and in masonry block or tile walls, provided they are not exposed to excessive moisture or dampness. The cable has a white PVC nylon insulation that is resistant to ozone, chemicals, radiation, weather, acids, alkalis, impact, abrasion, industrial solvents, oils, and flames.
NM cable is popular for residential wiring due to its ease of use and cost-effectiveness. It is lighter than metallic sheathed wiring, making it easier to unspool and straighten out. NM wire also pulls easily through holes in studs due to its smooth sheathing. In addition, NM cable is simple to cut and rip lengthwise since the sheathing is plastic. However, NM cable cannot be used in certain situations, such as outdoors or when wiring is exposed along the face of foundation walls. In these cases, the electrical code calls for conduit installations.
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Cannot be used outdoors or buried underground
NM cable, also known as Romex, is a type of electrical wiring commonly used in residential settings. It stands for "non-metallic" sheathed electrical cable, typically made of thermoplastic or PVC. NM cable is popular due to its ease of use, lightweight construction, and smooth sheathing, which makes it ideal for do-it-yourself electricians and professionals alike.
However, NM cable has certain limitations and cannot be used in all situations. One significant restriction is that NM cable cannot be used outdoors or buried underground. This limitation applies specifically to standard NM cable, which is designed for interior residential wiring within ceiling cavities or walls. While it is suitable for dry areas, it is not approved for outdoor exposure or underground burial.
The electrical code requires conduit installations for outdoor applications or when wiring is exposed along the face of foundation walls. NM cable also needs protection in certain situations, such as when it is not inside a wall. Additionally, NM cable cannot be used above drop ceilings in light commercial applications.
For underground applications, a different type of cable is necessary. The UF-B cable is specifically designed for underground use and features wire conductors embedded in solid plastic. This type of cable is typically used to run circuits to outdoor structures like sheds or garages or to power landscape features. It is important to follow the electrical code and choose the appropriate type of cable for each specific application to ensure safety and compliance.
While NM cable has its limitations, it remains a popular choice for residential wiring due to its ease of use and other advantages. However, it is crucial to be aware of the restrictions and select alternative cable types, such as UF-B, for outdoor or underground installations.
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Comes in different forms, including NM-8 and UF-B cable
NM stands for non-metallic cable, which is the most popular type of wiring in a home. It is also known as Romex, which is the brand name of one type of NM wire. NM wire is electrical wire with an outermost sheathing made of PVC. The sheathing bundles individual wires into a cable. The wires are copper and are individually coated in plastic. NM cable is used for nearly all residential electrical devices such as GFCI outlets, lights, and wall outlets. It is used in normally dry installations in residential wiring, as branch circuits for outlets, lighting, and other residential loads.
NM cable comes in different forms, including NM-8 and UF-B cable. Standard NM cable, or NM-8, is suitable for interior residential wiring within ceiling cavities or walls. It is known as NM-8 because it has a color-coded outer sheathing to quickly identify the wire gauge of the cable. For example, the 14-gauge wires cable has white sheathing and is used for 15-amp circuits, while the 12-gauge wires cable has yellow sheathing and is used for 20-amp circuits. This type of cable cannot be used outdoors or be buried underground.
UF-B cable, on the other hand, is a type of NM cable that can be used underground. It is a replacement for NMC and is typically used for underground direct burial installations. UF-B cable is suitable for wet, damp, and dry locations and can be used to distribute power from an existing building to outdoor lighting fixtures, pumps, outbuildings, and other outdoor equipment. It does not have an electrical conduit but is protected by durable rubber sheathing. When installed, UF-B cable must be buried at least 24 inches below the surface.
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NM wire is lighter and easier to unspool than metallic sheathed wiring
NM stands for non-metallic wire, which is an electrical wire with an outermost sheathing made of PVC. NM wire is frequently used in residential structures for interior wiring. It is also used in commercial wiring, industrial automation, telecommunications, and data transfer.
NM wire is lighter than metallic sheathed wiring, making it easier to unspool and straighten out. Its pliable PVC sheathing contributes to its ease of use. NM wire is also more affordable than metallic sheathed wiring, as it requires fewer tools and less labour for installation.
The individual wires within NM cable are typically made of copper, which can be either solid or stranded, and are coated in plastic or rubber. The plastic or rubber insulation prevents electrical currents from leaking out and making contact with other objects. The outermost sheathing of NM cable is made of sturdy and durable materials like PVC or nylon, which protect the cable from external factors such as moisture, heat, and physical damage.
While NM wire is versatile, it has some limitations. It is not suitable for outdoor use or in areas with exposed foundation walls. It also cannot be left exposed in projects such as hanging lighting fixtures. NM wire is also incompatible with heavy-duty applications as extreme temperatures can easily damage it.
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Frequently asked questions
NM stands for non-metallic sheathed electrical cable. It is a type of wiring that is commonly used in residential electrical wiring.
NM cable has an outer vinyl or PVC sheathing. The wires inside are made of copper and are individually coated in plastic.
NM cable is used for residential electrical wiring, such as GFCI outlets, lights, and wall outlets. It is suitable for use within ceiling cavities or walls and is known as NM-8.
