Understanding Type MC-HL Cable: A Guide to Class I, Division 1 Wiring

In heavy industrial facilities—such as petroleum refineries, chemical processing plants, pipeline compressor stations, and offshore drilling platforms—standard commercial electrical wiring methods are strictly prohibited by electrical safety codes.

To meet National Electrical Code (NEC) requirements for hazardous (classified) locations across Class I, II, and III environments, many project engineers and electrical contractors rely on Type MC-HL (Metal-Clad Hazardous Location) cable.

Whether you are designing a power distribution loop for a Class I, Division 1 facility or sourcing replacement inventory for an emergency plant turnaround, understanding MC-HL construction, compliance stamps, and inventory lead times is essential for keeping your job site fully compliant and on schedule.

Type MC-HL Instrumentation Cable: Cross-section showing corrugated welded aluminum armor with a PVC outer jacket, PVC inner protective jacket, overall aluminum/Mylar shield, and individual shielded twisted pairs.

What Does the "HL" Designation Stand For?

While standard Type MC (Metal-Clad) cable is widely used in commercial buildings and light industrial settings, the "-HL" suffix elevates the cable to a specialized code tier:

• Standard Type MC: Typically constructed with Aluminum Interlocked Armor (AIA) spiraled over insulated conductors. Under NEC Article 500/501, standard interlocked AIA cable is generally restricted to non-hazardous locations or Class I, Division 2 areas under specific conditions.

• Type MC-HL: Features a gas-tight, vapor-tight continuous corrugated metallic sheath (usually aluminum) encased inside a heavy-duty PVC or CPE outer jacket. The "-HL" stamp explicitly certifies that the cable is UL-listed (UL 2225) and code-approved for installation in Class I, Division 1 (and Zone 1) hazardous locations.

The CCW Connection: What Is Continuously Corrugated Welded Sheath?

When reviewing submittals, you will often hear Type MC-HL referred to as CCW cable.

• CCW (Continuously Corrugated Welded) describes the physical manufacturing process: a seamless, liquid-tight metal tube is continuously welded and corrugated around the conductor assembly.

• MC-HL is the official NEC/UL code designation printed on the cable jacket that permits its installation in Division 1 classified areas.

Standard Aluminum Interlocked Armor (AIA) allows gases, vapors, and moisture to migrate through the spiraled seams of the metal tape. In a Class I, Division 1 location, explosive vapors could travel inside an interlocked cable directly into non-classified control rooms or electrical switchgear. MC-HL’s impervious CCW sheath stops gas migration entirely.

Class I, Division 1 vs. Division 2: Where is MC-HL Required?

To specify the correct cable, estimators and engineers look directly at the NEC hazardous area classifications:

• Class I, Division 1 (and Zone 1): Flammable gases, vapors, or liquids exist in the atmosphere continuously, periodically, or during normal plant operations.

  • Code Requirement: Rigid metal conduit (RMC) with poured explosion-proof seals OR continuous metal-sheathed cable explicitly listed for Division 1—Type MC-HL.

• Class I, Division 2 (and Zone 2): Volatiles are handled or stored, but are only expected to escape in the event of an accidental rupture, equipment failure, or abnormal operation.

  • Code Requirement: A broader range of cable constructions (including tray cable and standard AIA interlocked armor) are permitted under specific code rules.

Key Physical Construction Layers

• Phase Conductors: Annealed flexible stranded copper (bare or tinned) insulated with high-dielectric XLPE (Cross-linked Polyethylene), PVC or EPR rated for 90°C wet/dry operation.

• Grounding Conductors: Bare or insulated grounding wires—frequently arranged in a 3-ground (split ground) symmetry to balance electromagnetic fields and optimize ground-fault clear paths.

• Continuously Corrugated Welded (CCW) Armor: A seamless, gas- and liquid-tight aluminum tube formed around the internal core assembly (replacing spiraled AIA tape).

• Overall Protective Jacket: A heavy-duty, flame-retardant, sunlight-resistant, and chemical-resistant outer sheath protecting the aluminum armor against direct burial soil chemicals and aggressive plant washdowns.

MC-HL vs. Rigid Metallic Conduit (RMC): Labor & Time Savings

Historically, Class I, Division 1 installations required threading rigid metal conduit (RMC) with explosion-proof seal-offs poured with liquid sealing compound. Replacing rigid conduit with Type MC-HL cable yields massive field installation benefits:

• Up to 50% Lower Installation Labor: MC-HL pulls directly through industrial cable tray systems without pipe bending, threading, or complex pulling stations.

• Elimination of Conduit Seal-Offs: When terminated with listed MC-HL explosion-proof cable glands (such as TMCX fittings with integral sealing compound), installers eliminate the need to thread and pour traditional conduit seal-off fittings (EYS seals) across every pipe run.

• Vibration & Impact Resistance: The corrugated aluminum armor absorbs heavy physical impacts and mechanical vibration from large industrial pumps and compressors better than rigid pipe.

• Direct Burial & Cable Tray Rated: Fully approved for outdoor cable trays, unistrut mounting, direct burial in trenches, and aerial runs.

Critical Installation Rule: Hazardous Location Cable Glands

Having a certified Type MC-HL cable is only half the compliance equation. A hazardous location rating is completely voided if the cable is terminated with standard commercial MC connectors.

To pass job-site inspection and maintain code compliance:

• Approved MC-HL Glands: Installers must use UL-listed MC-HL hazardous location connectors equipped with an elastomeric sealing ring and integral compound chamber (e.g., Crouse-Hinds TMCX series or Thomas & Betts Star Teck® XP series).

• 360° Armor Grounding: The fitting must securely grip the corrugated metallic sheath 360° around its circumference to ensure continuous ground-fault conductivity.

Sourcing Type MC-HL Cable Without Long Factory Delays

Procuring Type MC-HL cable often presents major supply chain challenges. Because manufacturing CCW continuous-welded armor requires specialized production mills, primary wholesalers and factories frequently have 8- to 16-week lead times and forced master reel minimum order quantities (MOQs).

At Wire America, we act as your agile supplying partner:

• Custom Cut-by-the-Foot Lengths: Order the exact footage your cable schedule requires—eliminating expensive job-site scrap and heavy spool handling waste.

• In-Stock Power & Control Sizes: We offer a comprehensive range of MC-HL control cables (16 AWG to 10 AWG) and heavy power feeders (8 AWG to 750 MCM).

• Fast Job-Site Shipping: Rapid dispatch from strategic distribution hubs keeps your turnaround schedule or emergency maintenance build on track.

Need Type MC-HL Cable for an Upcoming Project?

Don't let factory lead times delay your facility upgrade or plant turnaround. Contact the Wire America sales team today to check live inventory, request custom legths, or get a quick competitive quote:

• 📞 Call Us Direct: (833) 268-8644

• ✉️ Email Sales: sales@wireamerica.com

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⚠️ Important Disclaimer: Safety and Compliance

Wire America provides this information as a guide only. Electrical installations must strictly adhere to the National Electrical Code (NEC) and all state, local, and jurisdictional requirements, which vary widely. Always consult a licensed electrician, electrical engineer, or the local inspecting authority before purchasing material or starting any electrical project. Wire America assumes no liability for the installation, use, or interpretation of these guides.