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NM cable means nonmetallic-sheathed cable: insulated electrical conductors and an equipment-grounding conductor contained together in a nonmetallic outer jacket. NM-B is a common type for residential branch circuits, including outlets and switches, but it is intended for dry locations. The exact cable and installation rules depend on the product listing and the electrical code adopted where the work is done.
What does NM stand for?
NM stands for nonmetallic, describing the cable’s outer sheath. It identifies a cable type, not a particular wire size or conductor arrangement. NM-B is a widely used form of NM cable for residential branch-circuit wiring.
What is NM-B cable used for?
Southwire identifies its copper NM-B cable for outlets, switches, and other loads in exposed or concealed work in dry locations. The exact permitted applications and installation requirements must be checked against the locally adopted electrical code, including any local amendments.
What is NM-B cable made of?
In Southwire’s copper NM-B specification, insulated bare-copper conductors and a solid bare-copper equipment-grounding conductor sit beneath a PVC outer jacket. The insulated conductors use PVC insulation with a nylon sheath. These construction details describe that manufacturer’s specified product, not every cable sold as NM.
#1 Best Overall
- Wire Specification: Solid Indoor 14/2 NMB cable 100ft coil; Coated in Cable Jacket for easier pulling; stripping; and installation
- Wire Application: Energeaster Type NM-B (non-metallic 90° C) Copper Building Wire is commonly applied in residential building wiring as a branch circuit for switches and outlets and indoor applications inside wall cavities and attics
- Wire Power Rating: The voltage rating of the cable is 600 volts
- Wire Caution: NM-B cable may be run in air voids of masonry block or tile walls where such walls are not wet or damp locations
- Durable & Safer: 2 conductor, 14 gauge solid construction has the insulated conductors (Black and White) parallel; The ground wire is wrapped with fire-retardant paper and laid parallel between the insulated conductors; Ground wire is 14 gauge solid also; The jacket is white on 14 gauge NM-B wire
The number and colors of insulated conductors depend on configuration. In the cited Southwire specification, 2-conductor cable has black and white conductors; 3-conductor cable has black, red, and white; and 4-conductor cable has black, red, blue, and white. The product’s voltage rating is 600 volts.
Where can NM-B be used?
Southwire specifies its NM-B cable for exposed or concealed work in dry locations. Its specification also allows air voids in masonry-block or tile walls only when those spaces are not wet or damp. That is not permission to use NM-B wherever a cable is concealed: the location, exposure, protection, and local code requirements all matter.
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- Wire Specification: Solid Indoor 10/2 NMB cable 100ft coil; Coated in Cable Jacket for easier pulling; stripping; and installation
- Wire Application: Energeaster Type NM-B (non-metallic 90° C) Copper Building Wire is commonly applied in residential building wiring as a branch circuit for switches and outlets and indoor applications inside wall cavities and attics
- Wire Power Rating: The voltage rating of the cable is 600 volts
- Wire Caution: NM-B cable may be run in air voids of masonry block or tile walls where such walls are not wet or damp locations
- Durable & Safer: 2 conductor, 10 gauge solid construction has the insulated conductors (Black and White) parallel; The ground wire is wrapped with fire-retardant paper and laid parallel between the insulated conductors; Ground wire is 10 gauge solid also; The jacket is orange on 10 gauge NM-B wire
For a project in a potentially damp or wet area, do not assume NM-B is suitable. Check the product listing and the locally adopted code for a wiring method permitted in those conditions.
What do the temperature ratings mean?
Southwire states that the conductor insulation is rated 90°C, but that NM-B ampacity is limited to the value for 60°C conductors under the NEC. The 90°C insulation rating therefore does not, by itself, authorize using a higher ampacity when sizing or protecting a circuit. Conductor size and overcurrent protection must be determined for the specific application under the applicable code.
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- UL Listed - Meets UL83 and UL719 standards with a verifiable UL E-file number.
- NEC Residential Use - Suitable for indoor branch circuits and household wiring in dry locations.
- Solid Bare Copper - Two insulated 12 AWG copper conductors plus bare ground; no CCA.
- Durable NM-B Jacket - Yellow sheath resists abrasion and includes clear printed markings.
- Easy Installation - Smooth jacket and easy-to-strip insulation reduce installation time.
Can NM-B conductors be separated from the jacket?
No. Southwire says the individual conductors in its Type NM-B cable are not separately listed or marked as THHN, and are not permitted to be installed apart from the complete cable. Conductors routed inside boxes or panelboards for termination are treated as part of the complete cable assembly; that exception is not permission to strip out and use the conductors as a separate wiring method.
How should you identify the right NM cable?
Do not select cable by jacket color alone or assume a familiar configuration is correct for a particular circuit. Verify the cable’s listing and product specifications, then confirm the circuit requirements and local code before purchase or installation.
Rank #4
- UL Listed - Meets UL83 and UL719 standards with a verifiable UL E-file number.
- Residential NEC Use - Ideal for indoor branch circuits, switches, outlets and household wiring in dry locations.
- Solid Bare Copper - Two insulated 10 AWG copper conductors plus bare ground; no CCA.
- Durable NM-B Jacket - Industry-standard orange thermoplastic sheath with clear printed markings for easy identification.
- Easy Installation - Smooth jacket and easy-to-strip insulation help reduce install time.
- Conductor size: must suit the circuit’s required ampacity and applicable code.
- Conductor count: check the number of insulated conductors and whether the cable includes an equipment-grounding conductor.
- Material and length: confirm the conductor material and the amount needed for the project.
- Location and protection: check whether the cable is suitable for the actual environment and whether protection from physical damage is required.
- Listing and local rules: verify that the product and wiring method are allowed under the locally adopted code and amendments.
What does the NEC say about NM cable?
Code requirements depend on the NEC edition adopted by the local jurisdiction and any amendments. An NFPA CMP-6 Preliminary First Revision Report contains proposed Article 334 text, including the draft sentence, “The ampacity of Types NM and NMC cable shall be determined in accordance with 310.14.” The report is preliminary and marked subject to revision, so it is context for proposed language—not a statement of final code requirements or proof of what a jurisdiction has adopted.
Quick Recap
Best Value
- UL Listed - Meets UL83 and UL719 standards with a verifiable UL E-file number.
- NEC Residential Use - Suitable for indoor branch circuits and household wiring in dry locations.
- Solid Bare Copper - Two insulated 12 AWG copper conductors plus bare ground; no CCA.
- Durable NM-B Jacket - Yellow sheath resists abrasion and includes clear printed markings.
- Easy Installation - Smooth jacket and easy-to-strip insulation reduce installation time.
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