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Flexible raceways are used where a rigid wiring method would be difficult to install or where equipment movement, vibration, alignment, or service access requires flexibility. Common examples include flexible metal conduit, liquidtight flexible metal conduit, and liquidtight flexible nonmetallic conduit.
For the NASCLA Electrical Contractor Exam, you should be able to distinguish the principal flexible raceway systems, identify their NEC articles, determine where they are permitted, apply securing and supporting requirements, understand their limitations, and determine when a separate equipment grounding conductor is required.
Why Flexible Raceway Is Used
Flexible raceways provide a protected wiring path while allowing the raceway to bend, move, or accommodate equipment connections that would be difficult to make with rigid conduit. They are frequently encountered at motors, transformers, HVAC/R equipment, machinery, luminaires, pumps, and other equipment where alignment or vibration must be considered.
Flexibility does not eliminate NEC installation requirements. Each flexible raceway type has its own permitted uses, prohibited uses, fittings, trade-size limitations, securing and supporting requirements, grounding provisions, and environmental limitations.
Know the Flexible Raceway Articles
Several flexible wiring methods are covered in Chapter 3. They may look similar in the field, but their NEC requirements are not interchangeable.
Article 348 — FMC
Flexible Metal Conduit is a flexible metallic raceway commonly used for equipment connections and other dry-location applications where flexibility is useful.
Article 350 — LFMC
Liquidtight Flexible Metal Conduit combines a flexible metallic raceway with an outer covering designed to provide liquidtight characteristics.
Article 356 — LFNC
Liquidtight Flexible Nonmetallic Conduit is a flexible nonmetallic raceway intended for applications requiring flexibility and liquidtight construction.
Article 360 — FMT
Flexible Metallic Tubing is another flexible metallic wiring method with its own permitted uses and limitations and should not automatically be treated as FMC.
FMC
Flexible metal conduit is a helically formed metallic raceway that can be bent by hand and routed where rigid conduit would be difficult to align. Article 348 permits FMC to be installed exposed or concealed when the installation complies with the permitted-use provisions and does not fall within a prohibited use.
FMC is commonly associated with short equipment connections, but the NEC does not define FMC simply as a short piece of conduit. Longer installations are possible when all applicable support, use, fill, grounding, and installation requirements are satisfied.
Flexible Construction
The helically formed metal construction allows the raceway to bend without the field bending procedures required for rigid raceways.
Equipment Connections
FMC is commonly used to connect motors, transformers, luminaires, and other equipment where alignment or vibration makes rigid conduit less practical.
Exposed or Concealed
Article 348 permits FMC in exposed and concealed installations when other applicable conditions are satisfied.
Metallic Raceway
FMC can participate in the equipment grounding path only when the conditions established by Article 250 are satisfied.
FMC Is Not a General Wet-Location Raceway
Standard FMC does not provide the liquidtight outer covering found on LFMC. Where moisture, liquids, or outdoor wet-location conditions are involved, the installer must select a wiring method specifically permitted for that environment.
Do not select FMC simply because flexibility is desired. First determine whether the environmental conditions permit its use.
LFMC
Liquidtight flexible metal conduit is similar in basic concept to FMC but includes an outer liquidtight covering. This allows LFMC to be used in applications involving moisture, liquids, weather exposure, and certain corrosive conditions when the raceway and fittings are suitable for the environment.
LFMC is widely encountered in HVAC/R and industrial installations, particularly at outdoor condensing units, pumps, motors, refrigeration equipment, and machinery where both flexibility and environmental protection are needed.
Flexible Metallic Core
The metallic construction provides flexibility and mechanical protection similar in principle to FMC.
Liquidtight Covering
An outer jacket provides the liquidtight characteristics needed for many wet and outdoor equipment connections.
Listed Fittings
Liquidtight fittings must be appropriate for LFMC and installed so the completed connection maintains the required environmental protection.
Physical Damage Limitation
LFMC is not permitted where subject to physical damage, so another wiring method may be necessary in vulnerable locations.
LFNC
Liquidtight flexible nonmetallic conduit provides flexibility and liquidtight characteristics without a metallic raceway body. Article 356 establishes the requirements for LFNC, including permitted uses, prohibited uses, fittings, bends, securing, supporting, and installation limitations.
Because LFNC is nonmetallic, it cannot serve as a metallic equipment grounding path. Where equipment grounding is required, an appropriate equipment grounding conductor must be installed with the circuit conductors.
Nonmetallic
The raceway material is electrically nonconductive and corrosion resistant in many environments.
Flexible
LFNC can accommodate equipment alignment, vibration, and limited movement where permitted.
Liquidtight
The raceway system is designed for applications in which moisture protection is required when installed with suitable fittings.
Separate EGC
Because the raceway is nonmetallic, a qualifying equipment grounding conductor is required where the circuit or equipment must be grounded.
Flexible Does Not Mean Unsupported
Flexible raceway still requires securing and supporting. The ability of the raceway to bend does not permit it to hang freely from equipment or rest on piping, ceiling systems, ductwork, or other building components unless a specific NEC exception permits the installation.
Always identify the exact raceway type and then use its securing-and-supporting section.
FMC and LFMC Support Rules
Under the normal requirements of 348.30 and 350.30, FMC and LFMC must be securely fastened within 1 foot of each termination and must be secured and supported at intervals not exceeding 4½ feet. Specific exceptions modify these requirements in certain installations.
Because the exceptions are important, an exam question describing a short equipment connection, concealed fishing, an accessible ceiling, or required movement should be read carefully before applying the basic rule.
Identify the Raceway
Determine whether the wiring method is FMC, LFMC, LFNC, or another flexible system.
Locate the .30 Section
Use the securing-and-supporting section of the specific raceway article rather than applying rules from another flexible wiring method.
Check the Basic Rule
For FMC and LFMC, verify fastening near terminations and the maximum support interval.
Read the Exceptions
Determine whether the installation qualifies for a specific exception involving concealed fishing, required flexibility, luminaires, accessible ceilings, or another stated condition.
1 Foot and 4½ Feet
For a standard installation, FMC and LFMC are secured within 1 foot of the termination and supported at intervals not exceeding 4½ feet.
These numbers are useful to recognize, but do not stop reading the Code once you find them. The exceptions immediately associated with the rule can change the requirement for specific installations.
Equipment That Moves or Vibrates
One of the most important reasons to use flexible raceway is to prevent vibration or movement from being transferred into a rigid raceway system. Motors, compressors, pumps, and similar equipment can transmit mechanical vibration through rigid connections.
A short flexible connection can isolate that movement from the rigid raceway system. The raceway must still be installed within the limitations of its article, and the grounding path must remain effective despite the movement.
Motors
Flexible raceways can accommodate motor vibration and make terminal-box alignment easier.
Compressors
HVAC/R compressors and associated equipment can transmit vibration that should not be transferred into a rigid raceway system.
Pumps
Flexible connections can accommodate vibration and small alignment differences between the raceway system and pump equipment.
Movable Equipment
Some equipment requires limited movement after installation, making flexibility an intentional part of the wiring method rather than merely an installation convenience.
Can Flexible Metal Raceway Serve as the EGC?
FMC and LFMC are metallic, but that does not mean they automatically qualify as equipment grounding conductors in every installation. NEC 250.118 establishes specific conditions under which listed FMC and LFMC can serve as an equipment grounding conductor.
These conditions involve factors such as listed fittings, raceway trade size, circuit overcurrent protection, total flexible raceway length in the effective ground-fault current path, and whether flexibility is required because of vibration or equipment movement.
When Flexibility Is Required, Install a Wire-Type EGC
Where FMC or LFMC is used because flexibility is required to minimize vibration or to permit equipment movement after installation, a wire-type equipment grounding conductor must be installed with the circuit conductors.
This is especially important in the equipment connections where flexible raceway is most commonly encountered. Do not assume that the metal spiral alone provides an adequate fault-current path in an installation specifically requiring movement or vibration isolation.
Article 250.118 Matters
Where flexibility is not required, qualifying FMC or LFMC installations can serve as equipment grounding conductors if all applicable 250.118 conditions are satisfied. The limitations are intended to ensure that the flexible metallic path has sufficiently low impedance to carry ground-fault current effectively.
Listed Fittings
The flexible raceway must terminate in fittings suitable for maintaining the required electrical continuity.
Length Limits
The combined flexible raceway length in the effective grounding path is limited when the raceway itself is relied upon as the EGC.
Overcurrent Protection
The permitted use of flexible metallic raceway as the EGC is tied to specified circuit overcurrent-device limitations.
Raceway Size
Trade-size limitations also apply when FMC or LFMC is relied upon as the equipment grounding conductor.
LFNC Requires a Conductive Grounding Path
LFNC cannot carry ground-fault current as a metallic equipment grounding conductor because the raceway itself is nonconductive. Where connected equipment must be grounded, a wire-type equipment grounding conductor or another qualifying grounding means must be provided.
Metal equipment enclosures and boxes connected by LFNC must be bonded to that grounding path so fault current can return to the source and operate the overcurrent protective device.
Flexible Raceway Connections
Flexible raceways require fittings specifically designed and listed for the raceway type. A fitting for FMC is not automatically suitable for LFMC or LFNC, and a fitting that mechanically connects the raceway may still be unsuitable for a wet or liquidtight application.
Raceway Compatibility
The fitting must be listed or identified for the particular flexible raceway type being installed.
Environmental Rating
Where a liquidtight or wet-location installation is required, the fitting must maintain the environmental characteristics of the raceway system.
Mechanical Securement
The fitting must secure the raceway without damaging its flexible construction or allowing the raceway to pull free.
Bonding Continuity
Where metallic flexible raceway is relied upon in the grounding path, the fittings are an important part of maintaining electrical continuity.
Flexibility Does Not Eliminate Bend Limits
Although flexible conduit can be bent without a conventional conduit bender, the bends must not damage the raceway or reduce its internal diameter so severely that conductor installation is impaired.
Flexible raceway articles also limit the total equivalent bends between pull points. For common flexible conduit systems such as FMC and LFMC, the familiar maximum of four quarter bends, or 360 degrees total, applies between pull points.
Do Not Coil Excess Flexible Conduit
Using an unnecessarily long loop of flexible conduit can increase conductor-pulling difficulty, create poor mechanical support, increase impedance in a metallic grounding path, and produce an installation that is easily damaged.
Use the amount of flexibility required for the equipment and installation rather than treating flexible raceway as an unrestricted substitute for a properly planned raceway route.
Choosing Between FMC and Liquidtight Raceway
When equipment is installed outdoors or in another wet location, the raceway selection must account for moisture. Ordinary FMC does not become suitable for a wet location simply because its connection is short.
LFMC or LFNC may be appropriate where permitted because these raceways are designed for liquidtight applications. The fittings, conductors, equipment entries, and enclosures must also be suitable for the wet environment.
FMC
Commonly associated with dry-location flexible equipment connections and other applications permitted by Article 348.
LFMC
Provides a flexible metallic raceway with liquidtight characteristics for permitted wet or moisture-exposed applications.
LFNC
Provides flexible nonmetallic liquidtight construction and requires a separate conductive grounding path where equipment grounding is required.
Flexible Raceway Has Mechanical Limits
Flexible raceways are useful because they bend, but that same characteristic can make them more vulnerable to crushing, impact, abrasion, and mechanical abuse than rigid raceways. The permitted-use and prohibited-use sections of the applicable article must be checked wherever physical damage is a concern.
LFMC, for example, is not permitted where subject to physical damage. A location exposed to forklifts, vehicles, stored materials, tools, or severe impact may therefore require a more robust raceway system.
Rigid Raceway to Flexible Raceway
A common installation uses a rigid raceway system for most of the branch circuit and changes to flexible raceway for the final connection to the equipment. This arrangement combines the strength and support of the rigid system with the movement or alignment capability of the flexible section.
Route the Main Raceway
Use EMT, IMC, RMC, PVC, or another suitable wiring method to approach the equipment area.
Provide a Transition Point
Use a box, enclosure, or listed fitting arrangement appropriate for the wiring methods and environment.
Install the Flexible Section
Use FMC, LFMC, LFNC, or another permitted flexible method based on moisture, vibration, movement, and physical-protection requirements.
Maintain the Grounding Path
Install the required equipment grounding conductor and bonding connections based on the flexible raceway type and the conditions of Article 250.
HVAC/R Equipment Is a Common Example
An outdoor condensing unit may be supplied by a rigid raceway or cable system to a disconnect and then connected from the disconnect to the equipment using LFMC or LFNC. The flexible section accommodates equipment vibration and alignment while the liquidtight construction addresses the outdoor environment.
The installation must still satisfy branch-circuit, disconnecting means, grounding, conductor, wet-location, support, and equipment-specific requirements.
Identify Why Flexibility Is Needed
The reason a flexible raceway is being used can affect the Code answer. A short raceway used merely because it is convenient can have different grounding implications from a flexible raceway specifically needed for vibration isolation or equipment movement.
Identify the Raceway
Determine whether the problem involves FMC, LFMC, LFNC, FMT, or another flexible wiring method.
Identify the Environment
Determine whether the installation is dry, wet, outdoor, corrosive, concealed, exposed, or subject to physical damage.
Determine Why Flexibility Is Required
Look for vibration, movement, equipment alignment, service access, or simply installation convenience.
Check Securing and Supporting
Use the specific .30 section and evaluate any exceptions that fit the installation described.
Check the Equipment Grounding Path
Determine whether the raceway can qualify as the EGC or whether a wire-type equipment grounding conductor is required.
Check Fittings and Location Suitability
Verify that the raceway and fittings are listed and suitable for the environmental conditions.
Do Not Assume Every 6-Foot Flexible Connection Is Automatically Compliant
The NEC contains several important 6-foot provisions involving flexible raceways, but they apply only under specific conditions. A 6-foot length does not automatically satisfy support requirements, grounding requirements, equipment-use limitations, or wet-location requirements.
When you see a 6-foot flexible connection in an exam problem, determine which NEC rule is actually being tested before choosing an answer.
Code Locations to Know
Article 348
Flexible Metal Conduit.
348.30
Securing and supporting requirements for FMC, including the basic 1-foot and 4½-foot provisions and applicable exceptions.
Article 350
Liquidtight Flexible Metal Conduit.
350.30
Securing and supporting requirements for LFMC.
Article 356
Liquidtight Flexible Nonmetallic Conduit.
Article 250
Grounding and bonding requirements that determine whether a metallic flexible raceway can serve as an equipment grounding conductor and when a wire-type EGC is required.
250.118
Identifies recognized equipment grounding conductors and establishes conditions for qualifying FMC and LFMC installations.
300.11
General requirements for securing and supporting raceways, cable assemblies, boxes, cabinets, and associated wiring-system components.
Key Points to Remember
- FMC is covered by Article 348, LFMC by Article 350, and LFNC by Article 356.
- Flexible raceway is commonly used where vibration, movement, alignment, or equipment access makes rigid raceway impractical.
- FMC is metallic but does not provide the liquidtight covering found on LFMC.
- LFMC combines a flexible metallic raceway with a liquidtight outer covering.
- LFNC provides flexible liquidtight construction without a metallic raceway body.
- Flexible raceways still require securing and supporting.
- FMC and LFMC normally must be secured within 1 foot of a termination and supported at intervals not exceeding 4½ feet, subject to specific exceptions.
- The exceptions associated with flexible raceway support rules must be read carefully.
- FMC and LFMC can serve as equipment grounding conductors only when the conditions of Article 250 are satisfied.
- Where flexibility is required for vibration isolation or equipment movement, a wire-type equipment grounding conductor must be installed with the circuit conductors.
- LFNC is nonmetallic and therefore requires another qualifying equipment grounding path where grounding is required.
- Flexible raceway fittings must be listed or identified for the particular raceway and environment.
- Liquidtight raceway installations require fittings that maintain the required environmental protection.
- Flexible raceways are still subject to bend limitations and must not be damaged or excessively deformed.
- LFMC is not permitted where subject to physical damage.
- Outdoor equipment connections commonly use liquidtight flexible raceways because both flexibility and moisture protection are needed.
- A 6-foot flexible connection is not automatically Code compliant simply because of its length.
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