UL Standard Flexible Metal Conduit

Material Type

Description

Common Applications

Standards

Galvanized Steel

Carbon steel coated with zinc for corrosion resistance.

Indoor/outdoor wiring, general-purpose use.

UL 1, NEC Article 348

Stainless Steel

Higher corrosion resistance, suitable for harsh environments.

Chemical plants, marine, food processing.

UL 1, NEC Article 348

Aluminum (Less common)

Lightweight and corrosion-resistant, but not as common as steel.

Specialized applications where weight matters.

UL 1 (if listed)

Trade Size (Inch)

Metric Equivalent (mm)

Inner Diameter (Approx.)

Outer Diameter (Approx.)

Common Applications

UL Standard

3/8"

12 mm

~0.36" (9.1 mm)

~0.50" (12.7 mm)

Small wiring, control circuits, lighting

UL 1

1/2"

16 mm

~0.49" (12.4 mm)

~0.62" (15.7 mm)

Branch circuits, motors, appliances

UL 1

3/4"

20 mm

~0.70" (17.8 mm)

~0.82" (20.8 mm)

Larger power circuits, HVAC, industrial

UL 1

1"

25 mm

~0.95" (24.1 mm)

~1.10" (27.9 mm)

High-current wiring, feeders, machinery

UL 1

1-1/4"

32 mm

~1.25" (31.8 mm)

~1.44" (36.6 mm)

Industrial power distribution

UL 1

1-1/2"

40 mm

~1.48" (37.6 mm)

~1.68" (42.7 mm)

Heavy-duty applications, large cables

UL 1

2"

50 mm

~1.95" (49.5 mm)

~2.18" (55.4 mm)

Large feeders, data centers, substations

UL 1

Application

Usage Description

Key Benefits

Limitations

Commercial Wiring

Power and lighting circuits in offices, retail spaces, and commercial buildings.

Easy installation in tight spaces.

Not suitable for wet/damp locations.

Industrial Machinery

Protecting wiring in motors, control panels, and automated equipment.

Handles vibration and movement.

Requires grounding for NEC compliance.

HVAC Systems

Routing wiring for heating, ventilation, and air conditioning units.

Flexible for bends around ductwork.

May need additional sealing in moist areas.

Data/Telecom Installations

Shielding low-voltage cables (e.g., Ethernet, fiber) in raised floors or ceilings.

EMI/RFI protection (if properly grounded).

Limited fire resistance vs. rigid conduit.

Theatrical/Lighting Rigging

Temporary wiring for stage lighting, events, and movable fixtures.

Lightweight and adjustable.

Not for permanent outdoor use.

Appliance Connections

Wiring for industrial appliances, ovens, and HVAC units.

Resists physical damage.

Must comply with NEC fill capacity rules.

Retrofit/Renovations

Upgrading old wiring where rigid conduit is impractical.

No threading needed; cuts easily.

Less crush-resistant than rigid conduit.