Flexible Conduit: Tips on Construction and Material Choices

Flexible conduits are essential components in many electrical systems, offering protection and flexibility in various environments. However, electricians, contractors and installers often struggle to select the appropriate conduit that balances flexibility, durability and regulatory compliance. Choosing incorrectly can result in costly rework, system failures or even safety hazards in commercial applications.

Understanding the nuances of flexible conduit construction and material selections is essential for seamless installations and long-term reliability.

The four primary types of flexible conduits available in the market include:

• Jacketed Metallic Conduits: These conduits combine metal strength with a protective outer jacket, suitable for environments requiring both durability and protection against moisture and chemicals.
  
  
• Unjacketed Metallic Conduits: These are purely metallic conduits without an external jacket, offering excellent flexibility and mechanical protection. They are ideal for indoor applications where additional chemical or moisture protection is unnecessary.
  
  
• Nonmetallic Conduits: Made from materials like PVC, these conduits are lightweight and corrosion resistant. They are typically used in environments where metal conduits are too heavy, or corrosion is a significant concern.
  
  
• EMI/RFI Shielded Conduits: These conduits protect sensitive electronic equipment from electromagnetic interference (EMI) and radio-frequency interference (RFI), making them essential in applications like communications and military installations.

Core Construction: Squarelock vs. Interlock

The main differences between squarelock and interlock core constructions lie in their design and functionality.

Squarelock cores allow for the inclusion of packing materials like copper-clad aluminum or nylon within the convolutions, enhancing the physical properties based on product type.

In contrast, interlock cores lack this packing material, and their construction style is determined by the product’s trade size, type, and listed status.

The Role of Trade Sizes in Flexible Conduit Selection

Trade sizes significantly impact the selection of flexible conduits for various applications. The conduit size must be large enough to meet the maximum wire fill percentage and flexible enough to accommodate the specific installation requirements.

For instance, larger trade sizes might be necessary for applications involving a high volume of wires or cables, whereas smaller sizes may suffice for simpler installations.

Specific trade size considerations should be made based on the type of installation or environment. For example, space-constrained environments might require smaller conduits, whereas areas needing significant wire capacity would benefit from larger trade sizes. It is important to note that NRTL listings are unavailable for conduits above a 4” trade size, limiting the options for large installations.

Choosing the Right Core Material for Flexible Conduits

The core materials used in flexible conduits are crucial in determining their performance and durability. Common materials include:

• Hot-Dipped Galvanized Steel: This material is widely used for listed conduits because it is known for its durability and corrosion resistance under normal conditions.
  
  
• Aluminum: Preferred for applications where overall weight is a concern, aluminum offers good corrosion resistance but lacks the strength of steel.
  
  
• Stainless Steel: Highly valued for its strength and superior corrosion resistance, stainless steel is ideal for demanding environments.

The choice of core material affects the conduit’s performance, with considerations such as weight, strength, and corrosion resistance influencing the decision based on the installation’s specific needs.

Which Jacketing Material is Best for Flexible Conduits?

The jacketing material of a conduit provides additional protection and impacts its flexibility, temperature resistance, and environmental protection. Common jacketing materials include:

• PVC: An all-purpose material resistant to most chemicals and environmental conditions like UV exposure and oil. It is versatile and commonly used in various applications.
  
  
• Food-Grade PVC: Similar to standard PVC, it also meets food-grade standards, offering antimicrobial properties for use in food processing environments.
  
  
• Polyurethane: Known for its low smoke, zero halogen properties, and resistance to chemicals and environmental conditions. It is ideal for applications requiring stringent safety standards.

The choice of jacketing material influences the conduit’s flexibility and suitability for specific environmental conditions. For instance, TPR jackets are ideal for extreme temperature ranges, while PVC jackets offer broad chemical resistance.

The Benefits of Colored Conduit Jacketing

Colored conduit jacketing provides functional benefits, including easy identification and organization of building systems.

Specific colors denote distinct functions or systems, such as red for fire or emergency systems and blue for data centers or food-grade applications. This color coding helps streamline maintenance and enhances safety by distinguishing different system components.

Three Levels of Shielding Effectiveness

Flexible conduits can be equipped with additional shielding options to protect against electromagnetic and radio-frequency interference. Some are better than others.

Three common shielding types include:

• Good Shielding—SLA (Tinned Copper Braided): Type SLA, UL Listed like standard Type LA conduit, is enhanced with a tinned copper shielding braid over the inner steel core and under the PVC jacket. It operates from -30°C to 80°C (dry), 60°C (wet), and 70°C (oil) and provides at least 90% shielding coverage.
  
  
• Better Shielding—EMS (Bronze Core): Type EMS offers superior shielding compared to Type SLA and operates from -55°C to 105°C. It features a fully interlocked bronze strip core without a braided shield, covered by an all-temperature PVC jacket, creating a sealed, waterproof raceway when used with liquidtight fittings.
  
  
• Best Shielding—EMCS (Bronze Core with Tinned Copper Braid): Type EMCS combines the bronze core and PVC jacket of EMS with the tinned copper braid of SLA, providing additional screening. It offers the same working temperatures as EMS.

Shielding enhances the performance and safety of conduit systems by protecting sensitive electronic circuits from outside noise and emissions.

Types of Nonmetallic Conduit Construction

Nonmetallic conduits come in two main types:

• Type A: Constructed from a two-layer extrusion of flexible PVC, this type is best suited for indoor applications with minimal risk of mechanical damage.
  
  
• Type B: This product features a flexible PVC construction with a rigid PVC spine, which provides additional mechanical strength and makes it suitable for outdoor and buried applications.

Choosing between Type A and Type B depends on the specific environment and application needs. Type A is ideal for dynamic flexing, while Type B offers more robust protection.

Regulatory and Standards Compliance Requirements

Flexible conduits must comply with various standards, laws and regulations, such as UL, CSA, and NEC requirements.

These standards dictate acceptable wiring methods and product types, ensuring safety and performance in different applications. Compliance with these standards influences material and construction choices, guiding manufacturers to meet specific regulatory requirements.

Get Expert Recommendations

When selecting flexible conduits, customers often overlook critical factors like listing requirements and application-specific variables. Ensuring maximum performance and safety requires double-checking specifications and considering each installation’s unique needs.

Be sure to consult experts and follow best practices for optimal results, performance and safety. Contact us to learn more about selecting the proper flexible conduits for your specific needs.