What Are Flexible Metallic Conduit?

Flexible metallic conduit is a helically formed metal raceway designed to protect insulated conductors while allowing bends and movement that would be difficult with rigid metal conduit, EMT, or PVC. In trade use, FMC is often called metal flex or simply flex. It is commonly supplied in coils and terminated with dedicated flex connectors and couplings. Compared with liquidtight flexible conduit systems, standard FMC is generally chosen where liquid ingress is not the main concern. Compared with armoured cable, FMC is a raceway, so the installer pulls in separate conductors sized for the circuit and application.

Where Are Flexible Metallic Conduit Used?

FMC is widely used for final connections to vibrating or movable equipment, including fans, unit heaters, pumps, compressors, machine tools, and HVAC equipment. It is also common above suspended ceilings, in commercial tenant improvements, and in retrofit work where existing building conditions make straight raceway runs difficult. Short whips from a junction box to equipment are one of the most common applications. In industrial and commercial settings, FMC can also help when alignment is uncertain until equipment is set in place. It is less attractive for long exposed runs where a more rigid raceway gives cleaner support, easier pulling, and often lower installed cost.

How To Choose Flexible Metallic Conduit

Start with the conductors. Determine conductor size, quantity, insulation type, and whether a bonding conductor is required. Then choose a conduit trade size that gives workable fill and does not make pulling unnecessarily difficult. Next, review the route: short offsets and equipment whips favour FMC, while long runs with many bends may be better served by another raceway. Confirm the location conditions, especially dry versus damp or wet exposure, oil, washdown, corrosion, and mechanical abuse. Then match the fittings to the box type, knockout size, and bonding method. Finally, check whether the installation needs standard straight connectors, 45 deg or 90 deg fittings, insulated throat fittings, anti-short protection where applicable, or specific connector styles for equipment enclosures.

Trade Rules Of Thumb

For many equipment whips, electricians try to keep FMC runs as short and direct as practical to reduce sagging, simplify support, and make grounding continuity easier to manage. As a typical rule of thumb, flex is most attractive where a small amount of movement or misalignment exists, not as a substitute for planning an entire branch circuit raceway. Another practical rule is to leave enough slack for service access without creating loops that interfere with equipment removal or ceiling space. When pulling conductors, a slightly upsized raceway can save time if the run has several bends or if larger stranded conductors are used. These are practical trade guidelines only and are not a substitute for code tables, permitted-use rules, or manufacturer instructions.

Sizing Guidelines

FMC sizing is normally based on conductor count, conductor size, insulation type, and allowable raceway fill. As a practical buying guide, small control or branch-circuit whips often fit in smaller trade sizes, while motor feeders, multiple current-carrying conductors, or installations needing easier pulling may justify moving up one size. If the raceway will contain larger stranded conductors, compact bends, or several changes in direction, avoid sizing so tightly that pulling damages insulation or wastes labour. Also review fitting throat size and box entry space, because a raceway that technically fits the conductors may still be awkward at the terminations. Final sizing and conductor derating must be verified using the applicable Canadian code tables and the actual conductor data.

Common Installation Practices

Typical installation practice is to cut FMC cleanly, install listed fittings matched to the conduit type and trade size, secure the raceway to boxes and enclosures without distortion, and support it according to code and site conditions. Electricians often use FMC for short motor or HVAC whips where vibration isolation matters and where rigid raceway right at the equipment would be awkward. Good practice includes protecting conductor insulation at cut ends, avoiding over-tight bends that flatten the conduit, and keeping the route clear of sharp equipment edges. Where bonding continuity through the raceway is part of the design, fittings and installation quality matter. Where there is any doubt, many installers prefer to include an appropriately sized bonding conductor and verify continuity during testing.

Common Mistakes

One common mistake is using standard FMC where the environment really calls for a different wiring method, such as a liquidtight system or a more corrosion-resistant raceway. Another is undersizing the conduit, which turns a simple whip into a difficult pull and can damage conductor insulation at the fittings. Installers also run into trouble when they assume all flex fittings are interchangeable across conduit types or brands without checking listing and compatibility. Excessive unsupported length, sharp bends near connectors, and poor bonding continuity are other recurring issues. On retrofit jobs, a frequent purchasing mistake is ordering only the conduit and forgetting locknuts, bushings, bonding fittings, reducing washers, or angle connectors needed to finish the installation cleanly.

Brand Comparisons

Bridgeport is well known in the trade, especially for fittings and connection hardware, and is a sensible choice when you want a familiar brand for standard commercial and industrial flex terminations. Wheatland, T&B, and Atkore are also commonly specified or cross-shopped in metal raceway systems, often depending on distributor availability, project standards, and what is already installed on site. In many jobs, matching the existing fitting ecosystem or approved material list matters more than chasing a nominal brand preference. If the project already uses one of the major raceway systems throughout, staying consistent can simplify approvals and field installation. Bridgeport is a practical option for many standard applications, while some buyers may still prefer another market leader when they are matching an installed base, a consultant spec, or a contractor standard.

Related Products

Flexible metallic conduit is commonly purchased with flex connectors, couplings, locknuts, insulated bushings, bonding bushings, reducing washers, straps, hangers, junction boxes, device boxes, and pull conductors. Depending on the application, buyers may also need anti-short protection, angle connectors, grounding conductors, wire lubricant, and identification materials. For equipment connections, related items often include disconnects, cord grips, liquidtight fittings where conditions require them, and box supports for rooftop or mechanical room work. If the installation is part of a motor or HVAC connection, it is worth reviewing the full bill of material before ordering so the crew has the right fittings and support hardware on site.

Frequently Asked Questions

Is flexible metallic conduit the same as liquidtight conduit?

No. FMC and liquidtight flexible conduit systems are different products. Standard FMC is generally selected for dry indoor applications unless the complete assembly is specifically suitable for the actual environment. If moisture, oil, washdown, or outdoor exposure is involved, review whether a liquidtight wiring method is required.

When is FMC a better choice than EMT?

FMC is often the better choice for short equipment connections, vibration areas, and retrofit routing where rigid tubing would require more offsets and fittings. EMT is often more economical and cleaner for longer straight runs with regular support points.

Can FMC be used for grounding and bonding?

It can be part of the bonding path in some installations, but that depends on the complete wiring method, fittings, conductor sizes, and applicable code rules. Do not assume the raceway alone is acceptable in every case. Verify the bonding method for the specific installation and inspection authority.

How do I choose the right trade size?

Start with the number and size of conductors, then check raceway fill and pulling practicality. If the run has tight bends or larger stranded conductors, moving up one trade size may make installation easier. Final sizing must be confirmed from the applicable code tables and actual conductor specifications.

What fittings are usually needed with FMC?

Most installations need listed flex connectors or couplings matched to the conduit size and box entry, plus locknuts and sometimes insulated bushings or bonding hardware. Angle fittings, reducing washers, and straps may also be needed depending on the equipment and mounting arrangement.

Is Bridgeport a good choice for flexible conduit installations?

Yes, especially where Bridgeport fittings align with the job requirements and the contractor wants a widely recognized trade brand. It is a practical option for many standard commercial and industrial applications. If the site already uses another approved system, matching that installed brand may still be the better purchasing decision.