Liquidtight flexible metal conduit may serve as a grounding means in sizes up to and including

Code Change Summary: Changes were made regarding the size of flexible metal raceways permitted to be used as an equipment grounding conductor.

Not all equipment grounding conductors (EGC’s) in the NEC are required to be of the wire type. Often, a metal raceway itself can serve as the EGC without the need to pull an additional wire type EGC through the raceway.

There are several flexible and non-flexible metal raceways recognized in 250.118 as an EGC. Section 250.118(5) is all about listed flexible metal conduit or (FMC). In the 2014 NEC, in order to use a length of FMC as the sole EGC for the circuit, 4 rules must be followed:

• The conduit must be terminated in listed fittings.
• The circuit conductors contained in the conduit must be protected by an overcurrent device rated at 20 amperes or less.
• The combined length of FMC, flexible metallic tubing and liquidtight flexible metal conduit in the same ground-fault current path cannot exceed 6 feet.
• If used to connect equipment where 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 must be installed.

In the 2017 NEC another rule was added:

• The size of the FMC cannot exceed 1 ¼ inches.

This change was to align with the performance testing required in the UL Standard for Flexible Metal Conduit. Currently, the UL Standard evaluates FMC as to its ability to maintain a suitable equipment grounding path only for sizes up to 1 ¼ inch. Anything larger is not evaluated for grounding. For some reason, the 1 ¼ inch maximum size restriction has been a part of the UL Standard for quite some time but the NEC has never mentioned it as a requirement.

Below is a preview of Article 250. See the actual NEC text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2017 NEC edition of NFPA 70.

2014 Code Language:

250.118 Types of Equipment Grounding Conductors.

(5) Listed flexible metal conduit meeting all the following conditions:

1. The conduit is terminated in listed fittings.
2. The circuit conductors contained in the conduit are protected by overcurrent devices rated at 20 amperes or less.
3. The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground-fault current path does not exceed 1.8 m (6 ft).
4. If used to connect equipment where 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 shall be installed.

2017 Code Language:

250.118 Types of Equipment Grounding Conductors.

(5) Listed flexible metal conduit meeting all the following conditions:

1. The conduit is terminated in listed fittings.
2. The circuit conductors contained in the conduit are protected by overcurrent devices rated at 20 amperes or less.
3. The size of the conduit does not exceed metric designator 35 (trade size 1 ¼).
4. The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground-fault current path does not exceed 1.8 m (6 ft).
5. If used to connect equipment where 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 shall be installed.