Chapter 3 Requirements

Figure 01

Note: This article is based on the 2020 NEC.

How well you implement Chapter 3 requirements directly affects how well you implement Article 250.

Chapter 3 covers conductors [310], cabinets and meter socket enclosures [312], and boxes, conduit bodies, and handhole enclosures [314]. The remaining articles are specific to individual wiring methods such as cables [320 through 340], raceways [342 through 390], and cable tray [392].

Article 300
Article 300 contains the general requirements for NEC wiring methods. However, Article 300 does not apply to signaling and communications systems, which are covered in Chapters 7 and 8unless Article 300 is specifically referenced nor to integral parts of equipment [300.1(B)].

Conductors
You must install single conductors in a Chapter 3 wiring method [300.3(A)]. All conductors of a circuit, including the neutral and equipment grounding conductors (EGCs), must be in the same raceway, cable, trench, cord, or cable tray; except as permitted by 300.3(B)(1) through (B)(4) [300.3(B)].

Metal raceways, cable armor, and other metal enclosures must be metallically joined into a continuous electrical conductor to provide effective electrical continuity [300.10 and 250.4(A)(3)]. This establishes the effective ground-fault current path necessary for the circuit overcurrent protective device to operate in response to a ground fault [250.4(A)(5)].

Ex 1: Short lengths of metal raceways to support or protect cables don’t have to be electrically continuous or connect to an EGC [250.86 Ex 2 and 300.10 Ex 1].

Article 314
Article 314 contains the installation requirements for boxes, conduit bodies, and handhole enclosures.

You can use nonmetallic boxes only with nonmetallic cables and raceways [314.3], unless the raceways and cables are bonded together in the nonmetallic box. You must connect metal boxes to an EGC per 250.148 [314.4].

Each box must have a cover, faceplate, fixture canopy, or similar device [314.25]. Metal covers must be connected to an EGC in accordance with 250.110.

Metal covers and exposed conductive surfaces of handhole enclosures containing branch-circuit and feeder conductors must be bonded to an equipment grounding conductor sized in accordance with 250.96(A).

Article 320 Armored Cable (Type AC)
AC cable is an assembly of insulated conductors individually wrapped in wax paper (jute) and contained within a flexible spiral metal sheath. The metal sheath of Type AC cable provides an adequate path for fault current and can serve as an EGC [250.118(8)].

Article 330 Metal-Clad Cable (Type MC)
Type MC cable encloses insulated conductors in a metal sheath of either corrugated or smooth copper or aluminum tubing, or in spiral interlocked steel or aluminum.

A variation of this cable combines the metallic sheath with an uninsulated aluminum grounding/bonding conductor and is listed and identified as an EGC [250.118(10)b]. Figure 01. But traditional interlocked MC cable cannot serve as an EGC; therefore it must contain an EGC of the wire type per 250.118(1) and comply with 250.118(10)(a) and 250.122 [330.108].

Article 334 Nonmetallic-Sheathed Cable (Type NM)
NM cable provides minimal physical protection for the conductors, so the installation restrictions are stringent. Its low cost and relative ease of installation make it a common wiring method for residential and commercial branch circuits.

NM cable encloses two or more insulated conductors within a nonmetallic jacket [334.2]. It must have an EGC of the wire type [334.108].

Article 348 Flexible Metal Conduit (Type FMC)
FMC (“flex”) is a raceway of circular cross section made of a helically wound, formed, interlocked metal strips, listed for the installation of electrical conductors [348.2].

If flexibility is necessary to minimize the transmission of vibration from equipment, or to allow for equipment that requires movement, an EGC of the wire type must be installed with the circuit conductors per 250.118(5)(e) [348.60].

If flexibility is unnecessary, the metal armor of FMC can serve as an EGC if the circuit conductors contained in the raceway are protected by an overcurrent protective device rated 20A or less, and the combined length of the raceway in the same ground-fault return path does not exceed 6 ft [250.118(5)].

The equipment bonding jumper can be installed inside or outside the FMC. Where installed outside the FMC, the equipment bonding jumper can’t exceed 6 ft and must be routed with the FMC per 250.102(E)(2).

Article 350 Liquidtight Flexible Metal Conduit (Type LFMC)
LFMC is a flexible raceway of circular cross section, having an outer liquidtight, nonmetallic, sunlight-resistant jacket over an inner flexible metal core, with associated connectors and fittings, listed for the installation of electrical conductors [350.2].

LFMC is a commonly used for the same reasons as FMC, except you also want protection from liquids and some corrosive effects.

If flexibility is necessary to minimize the transmission of vibration from equipment, or to provide flexibility for equipment that requires movement after installation, an equipment grounding conductor of the wire type must be installed with the circuit conductors in accordance with 250.118(6).

If flexibility is not necessary after installation, and vibration is not a concern, the metal armor of liquidtight flexible metal conduit can serve as an equipment grounding conductor if the circuit conductors contained in the raceway are protected by an overcurrent protective device rated 20A or less, and the combined length of the raceway in the same ground-fault return path does not exceed 6 ft in accordance with 250.118(6).

Article 352 Rigid Polyvinyl Chloride Conduit (Type PVC)
PVC is a rigid nonmetallic, circular raceway with integral or associated couplings, listed for use with electrical conductors [352.2].

PVC provides many of the advantages of rigid metal conduit, while allowing installation in wet or corrosive areas. It is inexpensive, easily installed, lightweight, easily cut and glued, and relatively strong. However, PVC is brittle when cold and sags when hot.

If equipment must connect to an EGC, a separate EGC of the wire type must be installed inside the raceway [352.60]. Note that this provision applies to all non-metallic raceways.

Section 352.60 Ex 2: An equipment grounding conductor is not required in a service PVC conduit where the neutral is bonded to the equipment as permitted in 250.142.

Article 356 Liquidtight Flexible Nonmetallic Conduit (Type LFNC)
LFNC is a listed, circular raceway with an outer liquidtight, nonmetallic, sunlight-resistant jacket over an inner flexible core with associated couplings, connectors, and fittings [356.2].

An EGC is not required in a nonmetallic raceway supplying nonmetallic equipment because there is nothing in the nonmetallic box that requires a connection to an EGC.

Article 358 Electrical Metallic Tubing (Type EMT)
EMT is a lightweight, unthreaded thinwall circular metallic raceway. It is relatively easy to bend, cut, and ream [358.2]. When joined with listed fittings and enclosures as a complete system, it reliably provides physical protection for conductors and an effective ground-fault current path.

Because EMT is not threaded, all connectors and couplings are of the threadless type (either set-screw or compression). These provide for quick, easy, and inexpensive installations as compared to other metallic raceway systems.

Couplings and connectors must be made up tight to maintain an effective ground-fault current path to safely conduct fault current per 250.4(A)(5), 250.96(A), and 300.10 [358.42]. EMT can serve as an EGC [250.118(4)].

All Chapter 3 conduits have the word “conduit” in the name. EMT is tubing, not conduit.

Article 386 Surface Metal Raceways
Using a surface metal raceway is a common method of adding a raceway when exposed traditional raceway systems are unacceptable and concealing the raceway is economically infeasible. They come in several colors and are available with colored or real wood inserts designed to make them look like molding rather than raceways.

They are available in different shapes and sizes. They can be mounted on walls, ceilings, or floors. Some have separate compartments that permit separating power and lighting conductors from low-voltage or limited-energy conductors or cables (control, signaling, and communications cables and conductors) [386.70].

A surface metal raceway that is listed for grounding is suitable as an equipment grounding conductor in accordance with 250.118(14). To serve this purpose, fittings must be mechanically and electrically joined in a manner that does not subject the conductors to abrasion. Surface metal raceways that allow a transition to another wiring method, such as knockouts for connecting raceways, must have a means for termination of an EGC.

Article 392 Cable Trays
A cable tray is not a raceway, it is a support system for cables and raceways. Cable tray systems include ladder, ventilated trough, ventilated channel, solid bottom, and other similar structures. They are manufactured in many forms—from a simple hanger or wire mesh to a substantial, rigid, steel support system. Cable trays are designed and manufactured to support specific wiring methods, as identified in 392.10(A).

Metal cable trays can be used as EGCs where the conditions of 392.60 are met. For example, the trays and fittings are identified as an equipment conductor.

Needed for bonding
Chapter 3 provides specific installation requirements for conductors, cables, boxes, raceways, and fittings. You must get these right to create an effective equipment grounding (bonding) system.