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Can Romex® Be Used In A Commercial Building? Full Guide

A man installing wired in a newly built building.

Building codes are regularly re-evaluated to cater to new products or as new hazards are identified. An example of this is that for many years Romex® non-metallic (NM) sheathed electrical cable was not permitted to be used in commercial buildings; however, this position has changed.

Romex® non-metallic (NM) sheathed electrical cable can be used as the branch wiring in commercial grade in Type III, type IV, and Type V buildings. Romex® cannot be used in structures higher than three stories and must always be protected from fire with a fifteen-minute rated barrier.

Romex® non-metallic (NM) sheathed electrical cable is a lower-cost wiring product sold on Amazon that can be used for both branch wiring circuits and some applications where conventional metal-clad cable may traditionally be used.

The caveat is that it must always be used in conduits like this one on Amazon, and be protected from heat.

Romex® Can Be Used In Commercial Buildings, With Provisions

Romex® is a brand name for a non-metallic sheathed electrical cable assembly, which is manufactured in Carrollton, Georgia.

Like other products such as Hoover vacuum and Kleenex tissues, the brand name Romex® has become the generic name for non-metallic sheathed electrical cable.

Note: This post may contain affiliate links which will take you to online retailers that sell products and services. If you click on one and buy something, I may earn from qualifying purchases. See my Affiliate Disclosure for more details.

Romex® wire provides electrical energy to power lighting and communications circuits.

Romex® cables generally consist of several (up to three) thermoplastic high-heat, nylon-coated wires (THHN), which are bundled together and sheathed in polyvinyl chloride (PVC).

THHN wires can be used in isolation or grouped within a Romex® wire cable.

Romex® cable is manufactured to handle the following specifications:

  1. A maximum voltage of 600 volts.
  2. Able to conduct the maximum ampacity limit of up to 140 degrees Fahrenheit.
  3. It can operate in temperatures up to 190 degrees Fahrenheit in dry environments.

Romex® cable is manufactured in seven gauges with two or three conductors inside:

  1. 14 gauge
  2. 12 gauge
  3. 10 gauge
  4. 8 gauge
  5. 6 gauge
  6. 4 gauge
  7. 2 gauge

The different categories of Romex® are identified by the:

  • color jacket
  • gauge
  • number of conductors contained within
CodeAmerican Wire Gauge (AWG)Number of Conductors
White Romex® 14/3143
White Romex ® 14/2142
Yellow Romex® 12/3123
Yellow Romex® 12/2122
Orange Romex® 10/3103
Orange Romex® 10/2102
Gray Romex® 8/383
Gray Romex® 8/282
Gray Romex® 6/363
Gray Romex® 6/262
Gray Romex® 4/343
Gray Romex® 4/242
Gray Romex® 2/323
Gray Romex® 2/222

Romex® Nonmetallic Sheathed Cable meets all the standards required by the following safety bodies:

  1. REACH stands for the Registration, Evaluation, Authorization, and Restriction of Chemicals.
  2. RoHS is the body controlling the Restriction of Hazardous Substances.
  3. NFPA the National Fire Protection Agency is responsible for setting the building codes related to fire hazards.
  4. ASTM is the acronym for the American Society for Testing and Materials.
  5. UL stands for Underwriters Laboratory standards number 83 and 719.

What Are The Different Kinds Of Cable Assemblies?

There are six types of cable assemblies most sold on Amazon that I’ve linked to where available, which are optimized for different wiring arrangements, as follows:

  1. (Types NM, NMC, NMS).
  2. Armored cable (type AC).
  3. Metal-clad cable.
  4. Mineral-Insulated, Metal-Sheathed Cable (Type MI Or MIMS).
  5. Service-Entrance Cable (Types SE, SER or SEU).
  6. Underground Feeder And Branch-Circuit Cable (Type UF).
Several colors of cables being installed in a newly built building.
There are several types of cable assemblies

Romex® Nonmetallic Sheathed Cable NMS (Types NM, NMC)

Romex®  Nonmetallic sheathed cable may be used for electrical installations in residential and light commercial buildings.

  1. The wiring type NM is sheathed in a non-metallic jacket.
  2. The wring-type NMC is sheathed in a corrosion-resistant, non-metallic jacket.

Non-metallic sheathed cables can be used in the following building types:

Type III Buildings

Type III buildings have exterior walls constructed from:

  • brick
  • masonry
  • concrete block
  • precast panels
  • other non-combustible materials

Type IV Buildings

Type IV uses nonstandard construction materials for the external walls and heavy timber for the interior walls.

The timber framing used for the beams and girders in Type IV  buildings is heavier and thicker, providing greater fire resistance than traditional timber-framed houses. While this timber will char and smolder, it provides the occupants with sufficient time to escape from the building.

Type V Buildings

Type V buildings are built using wood and have no fire retardant rating.

Type V buildings tend to be smaller than the other grades of construction; however, the building material is used for small commercial structures such as restaurants and smaller office buildings.

The types of buildings in which Romex® Nonmetallic sheathed cable may be used are:

  1. One- and two-family dwellings.
  2. The attached or detached garages at one- and two-family dwellings.
  3. Storage buildings at one- and two-family dwellings.
  4. Dwellings are designed to house more than one family as long as they are of Types III, IV, and V construction.
  5. Any other structures are classified as Types III, IV, and V construction.

Romex® Nonmetallic sheathed cable may not be used in residential or commercial constructions higher than three stories.

There are two provisions regulating the use of Romex® Nonmetallic sheathed cable:

  1. The Romex® Nonmetallic sheathed cable must be concealed within walls, floors, or ceilings and protected in conduit.
  2. The Romex® Nonmetallic sheathed cables are protected by a thermal barrier material that will survive for at least fifteen minutes as specified in the listings of fire-rated assemblies.

The Romex® Nonmetallic sheathed cable can be used in locations that are:

  • dry
  • moist
  • damp
  • corrosive

The following Romex® non-metallic sheathed cable categories will be used in a standard building:

Service Entrance Cable

A two-wire Romex® non-metallic sheathed cable will be used as the service entrance cable.

Branch Line Cable

A three-wire Romex® non-metallic sheathed cable will be used in the branch line circuits of the electrical installation, which allows for the ground wire to be incorporated for most electrical consumers. This will be set up as a 15 Amp circuit that leads to one or two separate switches.

Armored Cable (Type AC)

Where necessary, armored cables are used for the branch-circuit connections from the main circuit board to the various branch lines within a building.

The branch circuits are 120-volt lines used to power the lights and other low-power energy drawing equipment, or they are 240-volt lines dedicated to certain high-draw equipment, such as stoves or air conditioners.

A metal sheath or aluminum armor cable is typically used for projects and can be used in these branch lines:

  • institutional
  • industrial
  • commercial

If an armored cable is not required, Romex® cable may be used for branch line circuits.

Cables buried underground running through the dirt.
Underground cables must run through a conduit or be metal-clad

Metal-Clad Cable

Metal-clad cables are used for underground wiring for installations.

The most commonly used product consists of three wires (two circuit conductors and a green equipment grounding conductor) encased in a flexible metal covering, most commonly made from aluminum.

NOTE: If metal box fittings for switches and plugs are used, only metal-clad cables may be used.

The aluminum shroud around the cables is flexible but holds its shape while being installed, making it an easy product to work with. The metal-clad cable can be buried directly underground or run through a conduit.

Mineral-Insulated, Metal-Sheathed Cable (Type MI Or MIMS)

A mineral-Insulated electrical cable is manufactured by placing copper conductors within a copper sheath which is then insulated using inorganic magnesium.

MIMS cable is used in these environments:

  • harsh
  • high-wear
  • high-temperature

The copper (or other metal) sheath protects the conductor wires from oxidation if used in wet or chemical environments. MIMS is used in nuclear power plants to wire the equipment used to measure the core temperatures.

The mineral casing is a barrier to:

  • oils
  • solvents
  • water
  • other chemicals

Service-Entrance Cable (Types SE, SER Or SEU)

The power utilities use service entrance cables to carry current into the building. There are two categories of service entrance cables:

  1. Service-Entrance Cable (SER).
  2. Service-Entrance Cable (SEU).

Service-Entrance Cable (SER)

SER cables are made from copper or aluminum and have a reinforcing tape.

Service-Entrance Cable (SEU)

SEU cable is not reinforced and is generally used in protected spaces, such as in a loft or within the circuit box, to carry power from the main switch to the branch lines.

Both categories of service-entrance cable should be rated:

  1. 120 v and 240 v and can be rated up to 600 volts.
  2. Temperatures of 194 degrees F
  3.  90 Amps (CMR) or 60 Amps (CM).

NOTE: Romex® cable can be sued for the service-entrance cable.

A man installing wiring in a newly built building.
SEU cables run to the branch lines

Underground Feeder And Branch-Circuit Cable (Type UF)

Underground feeder cables have many similarities with Romex® cables. The main difference is that Underground feeder cables have a stronger and more durable outer sheath.

The strength and durability of the outer sheath give the underground feeder the designation UF which means that the wire is more suitable for use underground or in damp areas.

One or more conductor wires are sheathed in a covering of non-metallic, flame-retardant material that is resistant to:

  • moisture
  • fungus
  • corrosion

Underground feeder wires can be used in the following applications.

  1.  Underground, including direct unprotected burial.
  2. As single-conductor cables.
  3. For wiring in wet, dry, or corrosive locations.
  4. Installed as nonmetallic-sheathed cable.
  5. A single conductor is used as the non-heating lead for heating cables.

The gauge conductors used in an underground cable are: 

  • 14 AWG copper
  • 12 AWG aluminum
  • copper-clad aluminum through 4/0 AWG


The most suitable cable Romex® non-metallic (NM) sheathed electrical cable may be used within a commercial building. The provisions are that a fifteen-minute heat-resistant barrier must protect it and be used in conduit.

It can be used in Type III, IV, and Type V buildings; however, it is not permitted in buildings with more than three stories.

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