Installing Flexible Conduit: NEC Code Requirements You Need to Know

Electrical failures, increased fire risks, compromised system integrity—so much can go wrong when you don’t install flexible conduit correctly.

Non-compliance with the National Electrical Code (NEC) not only jeopardizes a project’s safety but can also lead to significant setbacks, such as costly rework, failed inspections, legal liabilities and damage to your professional reputation.

Whether it’s exceeding a conduit’s bend radius, neglecting grounding requirements or using the wrong type of electrical conduit for a particular environment, even small mistakes can have big consequences.

That’s why electricians, contractors and installers should have a thorough understanding of the NEC’s requirements for flexible electrical conduits to reduce these risks.

That’s what we’re here to discuss.

This blog explores the critical guidelines for flexible conduit installations, offering insights into conduit types, installation standards and best practices to ensure safety, compliance and repeat business.

NEC Guidelines for Flexible Conduits

The NEC provides detailed requirements for flexible electrical conduits across several key articles. They include:

• Article 348 governs Flexible Metal Conduit (FMC), commonly used for dry applications requiring a flexible connection.
• Article 350 covers Liquidtight Flexible Metal Conduit (LFMC), specifying its use in environments requiring moisture protection.
• Article 356 focuses on Liquidtight Flexible Nonmetallic Conduit (LFNC) and highlights its corrosion-resistant, nonmetallic properties for specific applications.

One thing to keep in mind: A recent update to the NEC permits the use of stainless steel for flex conduit when installed with a separate grounding conductor or bonding jumper, broadening its application scope.

How to Choose the Right Conduit for the Job

The choice of flexible conduit depends on the specific needs of the installation.

Flexible conduits, like FMC, are ideal for general dry locations, while LFMC offers added protection in environments exposed to moisture or liquids.

LFNC, being non-metallic, is suited for applications requiring resistance to corrosion.

Flexible conduits are particularly useful in scenarios where a rigid conduit system would be impractical, such as in motor connections, vibrating equipment, or installations in confined spaces.

The NEC underscores the importance of using listed conduits for all flexible applications to ensure safety and compliance. For example, LFMC is preferred for environments requiring additional protection against liquids or hazards. However, the final application of a flexible conduit depends on various factors, including environmental conditions and specific project requirements. 

Installation Standards: Ensuring Proper Use

Proper installation of flexible conduits is critical for compliance and safety. The NEC outlines standards that cover everything from minimum bend radius to support spacing and slack considerations.

One key factor is adhering to the conduit’s minimum bend radius to prevent damage and maintain its structural integrity. Contractors should also ensure the conduit is adequately supported at regular intervals as specified by the NEC, which helps maintain its alignment and functionality.

Additionally, allowing for sufficient slack during installation prevents undue tension and preserves flexibility.

When installing flexible conduit, contractors should account for the conduit’s inherent flexibility to avoid cutting lengths too short or tight. For example, conduits may contract or stretch slightly, so leaving extra slack is a practical approach to ensure a secure fit without over-stressing the conduit.

Safety and Grounding Requirements for Flex Electrical Conduit

The NEC emphasizes the importance of grounding and bonding to maintain electrical safety in flexible conduit installations.

Listed FMC and LFMC conduits have specific grounding requirements that vary based on factors like the length of the conduit and the application type. These requirements ensure the flex conduit system remains safe and functional under various conditions.

In hazardous environments, such as those defined under Articles 501, 502 and 503, the NEC permits using listed conduits depending on the specific hazard criteria. However, it’s important to note that flexible electrical conduits are not rated for Class 1, Division 1 explosion-proof applications. Contractors must always verify the suitability of a product for hazardous locations before installation.

Regional and Local Considerations

While the NEC provides a national standard, regional and local amendments may impose additional requirements.

For instance, Chicago mandates specific conduit types, such as Plenflex, for certain applications. Contractors working in different jurisdictions should collaborate with local electricians or authorities having jurisdiction (AHJ) to ensure compliance with regional codes.

Preparing for Inspections

NEC compliance is typically verified during inspections, where inspectors ensure proper installation and application of listed flexible conduits.

Inspectors often check for specific markings on conduit jackets, which indicate their listing and suitability for particular uses. To streamline the inspection process, contractors can proactively consult with inspectors before starting an installation. This approach ensures compliance and helps avoid potential delays or costly rework due to unforeseen issues.

Being prepared with accurate documentation and following NEC guidelines can make inspections for flex conduit more efficient and successful.

Best Practices for Flexible Conduit Installation

While the NEC provides the minimum standards for flex electrical conduit installations, adhering to best practices can further enhance safety and performance.

For example, never flex a conduit beyond its marketed bend radius, and carefully consider the role of connectors and angled connections in the overall installation. Allowing for flexibility and slack is also essential to avoid unnecessary tension in the system.

Following the NEC and consulting with inspectors and local AHJs remain the most reliable strategies for ensuring compliance and avoiding mistakes. To achieve the best results, contractors should approach flexible conduit installations with precision and attention to detail.

Key Takeaways for Installing Flex Conduit

Understanding and applying the NEC requirements for flexible electrical conduit is essential for safe and effective electrical installations. You can ensure compliance and safety by familiarizing yourself with the relevant articles, choosing the appropriate conduit for the job and adhering to installation standards.

Best tip: Always refer to the NEC, stay updated on revisions and collaborate with inspectors to ensure durable conduit installations that meet standards and drive repeat business.