Note: The equipment grounding conductor is intended to serve as the effective ground-fault current path. See 250.2.
Author’s Comment: The effective ground-fault path is an intentionally constructed low-impedance conductive path designed to carry fault current from the point of a ground fault on a wiring system to the electrical supply source. Its purpose is to quickly remove dangerous voltage from a ground fault by opening the circuit overcurrent device [250.2]. Figure 250–84
Figure 250-84
(1) A bare or insulated copper or aluminum conductor sized in accordance with 250.122.
Author’s Comment: Examples include PVC conduit, Type NM cable, and Type MC cable with an equipment grounding conductor of the wire type.
(2) Rigid metal conduit (RMC).
(3) Intermediate metal conduit (IMC).
(4) Electrical metallic tubing (EMT).
(5) Listed flexible metal conduit (FMC) where: Figure 250–85
Figure 250-85
a. The raceway terminates in listed fittings.
b. The circuit conductors are protected by an overcurrent device rated 20A or less.
c. The combined length of the flexible conduit in the same ground-fault current path doesn’t exceed 6 ft. Figure 250–86
Figure 250-86
d. If flexibility is required 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 250.102(E), and it must be sized according to 250.122, based on the rating of the circuit overcurrent device.
(6) Listed liquidtight flexible metal conduit (LFMC) where:
Figure 250–87
Figure 250-87
a. The raceway terminates in listed fittings.
b. For 3⁄8 in. through ½ in., the circuit conductors are protected by an overcurrent device rated 20A or less.
c. For ¾ in. through 1¼ in., the circuit conductors are protected by an overcurrent device rated 60A or less.
d. The combined length of the flexible conduit in the same ground-fault current path doesn’t exceed 6 ft.
e. If flexibility is required 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 250.102(E), and it must be sized in accordance with 250.122, based on the rating of the circuit overcurrent device.
(8) The sheath of Type AC cable containing an aluminum bonding strip. Figure 250–88
Figure 250-88
Author’s Comments:
• The internal aluminum bonding strip isn’t an equipment grounding conductor, but it allows the interlocked armor to serve as an equipment grounding conductor because it reduces the impedance of the armored spirals to ensure that a ground fault will be cleared. It’s the aluminum bonding strip in combination with the cable armor that creates the circuit equipment grounding conductor. Once the bonding strip exits the cable, it can be cut off because it no longer serves any purpose.
• The effective ground-fault current path must be maintained by the use of fittings specifically listed for Type AC cable [320.40]. See 300.12, 300.15, and 320.100.
(9) The copper sheath of Type MI cable.
(10) Type MC cable that provides an effective ground-fault current path in accordance with one or more of the following:
(a) It contains an insulated or uninsulated equipment grounding conductor in compliance with 250.118(1). Figure 250–89
Figure 250-89
(b) The combined metallic sheath and uninsulated equipment grounding/bonding conductor of interlocked metal tape-type MC cable that’s listed and identified as an equipment grounding conductor. Figure 250–90
Figure 250-90
Author’s Comment: Once the bare aluminum grounding/bonding conductor exits the cable, it can be cut off because it no longer serves any purpose. The effective ground-fault current path must be maintained by the use of fittings specifically listed for Type MCAP® cable [330.40]. See 300.12, 300.15, and 330.100. Figure 250–91
Figure 250-91
(c) The metallic sheath or the combined metallic sheath and equipment grounding conductors of the smooth or corrugated tube-type MC cable that’s listed and identified as an equipment grounding conductor.
