Article 334 of the National Electric Code (NEC) is devoted to installing and using unpleasant cables, including NM species (commercially known as Romex in the United States), NMC and NMS. These cables are used in the residential wire of the branch and lighting circles. Article 334 determines the rules that these cables can be used, how to install, and where they are banned. Below is a comprehensive overview of the most important aspects of NEC 334.
Article 334
Article 334 covers the combined cables with two or more isolated conductors (with or without a ground wire) surrounded by a non -metallic dip (usually PVC or nylon). These cables are intended for use in dry and protected sites in residential and light commercial applications.
Types of the non -average cable (definitions)
Write NM: Standard Romix cable used in the inner dry sites. It has two or more insulated conductors with or without the bare ground wire.
Write NMC: Moisture, corrosion, and fungi resistance; Suitable for wet environments.
Write NMS: It contains energy and signs under the same sheath. This is a rare type of cable that is not widely used today.
Where the NM cable (334.10) can be used
Below is the full list of all sites allowed for non -metal cables:
One housing and two family: Open or hidden.
Multiple family housing (Third Type, Fourth, V Building): Hide in the walls, floors or ceilings with a 15 -minute fire barrier.
Other buildings: Only where it is hidden inside the walls/floors/ceilings with the thermal or explicitly permitted protection.
Cable trays: NMC/NMS only, if not damaged. NM-B is not allowed.
Open work: In garages, lower floors, and crawling spaces if they are closely followed the frame and protection from damage. Also in storage areas of one housing or family.
Where the NM cable (334.12) cannot be used
Sites exposed to material damage
Air processing spaces (His Majesty Makmoura)
Integrated into the coincidence concrete unless it is protected by the channel or the sleeves
Dangerous sites (classified)
Outdoor or in wet environments
Main installation rules
Rulings with a diameter (334.24): Minimum 5 x cable diameter.
Insurance and support (334.30): It should be secured within 12 inches of boxes and support every 4.5 feet. Support options include pins, cable relationships, or tapes that do not harm the closer.
Protection (334.15): Required in the regulations, crawling spaces, and grooves where the cables are detected. Protection means include channels in uninterrupted lower garages or floors, guard ribbons in areas that can be accessed for storage, framing or racing in cultivated areas. It should be protected within 6 feet from the entrance to the attic.
Through holes (334.17): The cable that passes through the wood frame should be 1.25 inches from the edge or a wetter with a steel plate.
The summit of the conductor and the temperature classification (334.80)
Nanometer cable He should Use the ampacity classification of 60 ° C even if the connectors are classified for higher temperatures. Therefore, for example, if the NM cable contains the THN conductor, you still have to rely on 60 ° C. This mandatory deviation is explained by two factors. First, the NM-B Cover often cannot deal with higher temperatures. Second, this is required under fire safety rules and UL menu requirements.
NMC/NMS cable Temperature assessments may be used higher when allowing. You must check the menu to find out for sure this is the case.
Collected cables It should be derived according to NEC 310.15. The combined cables should be extracted under the NEC 310.15 by reducing their permissible capacity based on the number of wires that are assembled together, since tightly packed wires cannot release heat easily and more vulnerable to high temperature.
For example, if you turn on five cables of 12 AWG NM with two wires currently carry each of them, you will have 10 connectors, which requires 50 % of the subscription, which falls from 20 amps to 10 amps only for each conductor.
Building specifications (334.100)
NM cable for internal use only and should remain dry.
It is only allowed to copper connections in the NM cable.
Not suitable for underground operation, outdoor exposure, or concrete inclusion without protection.
The NM cable cannot be parallel to what is not exactly allowed.
Cable Model requirements (334.112)
Cables must be marked:
Cable type (NM, NMC, NMS)
The size of the conductor and its number
Viturable Classification (Usually 600 V)
The name of the manufacturer or the brand
UL menu
Common inspection red flags
watch:
The NM cable works outside (even below the deck) without NMC or sleeves.
NM cable is loose or not supported in crawling or garage spaces.
Bored boredom holes without degrated modifications.
An unprotected cable extends across the floor or below the rafters.
NM cable stuffed in metal boxes without the right clamps or relieving stress.
Why is the NM cable be banned in some areas
The use of NM cable is prohibited to use it by some local restrictions, including:
Chicago:
Its electric code is used, not NEC.
Metal races (EMT, MC) require all wires.
The main factors include firefighting, old law practices, and trade union work standards.
New York City:
NEC depends with large -scale adjustments.
NM cable is not allowed; MC and EMT are required for safety in high buildings and buildings with fire -classified gatherings.
Parts of California:
Seismic activity calls for more flexible and powerful wires (for example, MC).
Easy flammable calm areas are easily flammable, so the use of NM may be completely dangerous.
Local modifications in cities such as San Francisco and Los Angeles restrict NM for MC or channel systems.
In conclusion, Article 334 NEC creates clear guidelines for using unreasonable cables in residential and light commercial applications. Although the NM cable remains an effective and cost -effective option, it should be used within strict limits and is prohibited in many high -risk or high -density judicial states.
Nasso Kabul National NM is compatible with the NEC 334. Always check your local authority that has a jurisdiction (AHJ) before choosing the types of cables for installation.
Below are the most popular cables:
2/14 Nanometer B – For 15A lighting and public outlets.
3/14 Nanometer B -3A 3A lighting circuits.
12/2 Nanometer B – For kitchen, bathroom, and port circles.
3/12 Nanometer B 20A vessels divided and triple switches.
10/2 nm For 30A water heaters and A/C.
10/3 Nanometer B – For 30A electric dryers and small devices.
8/3 Nanometer B – For 40A electrical domains and dryers.
6/3 Nanometer B-50A Furniture, Spanders, and SubPanels.
