Electrical Reference Library · Measure & Identify

How to Identify Conduit Types

Field identification of EMT, IMC, RMC, PVC, ENT and flexible conduits by wall thickness, threads, markings and fittings, plus the trade-size-to-metric-designator crosswalk.

Ref EL-0066NEC 342NEC 344NEC 352NEC 358NEC 362UL 6UL 797UL 651

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Conduit is the tube or raceway that protects and routes conductors. Each type has its own NEC article and its own product standard. Fittings, supports and permitted uses differ between types, so you need to know the type before you sell couplings, connectors or straps.

How to identify

Magnet test. A magnet sticks to steel EMT, IMC and RMC. It does not stick to aluminum, PVC, ENT or nonmetallic flexible conduit.
Look for threads. RMC and IMC are sold threaded on both ends with a coupling on one end. EMT is never threaded. It joins with set-screw or compression fittings.
Compare wall thickness. Thinnest to thickest: EMT, IMC, RMC. For the same trade size, IMC and RMC have about the same OD, but IMC has a thinner wall and is lighter.
Read the markings. Look for the printed or stamped type (EMT, IMC, RMC or "Rigid", Schedule 40 or 80 PVC), the trade size, the manufacturer and the listing mark. Steel conduit usually carries these on a label or ink line along each length.
Check for flexibility. FMC is bare interlocked metal. LFMC is metal core with a plastic jacket. LFNC is all plastic. ENT is corrugated plastic tubing that bends by hand.

Identification table

Type	NEC article	Material	Joins by	Quick tell
EMT	358	Steel or aluminum, thin wall	Set-screw or compression fittings	Unthreaded, light, bends easily with a hand bender
IMC	342	Steel, intermediate wall	Threaded couplings	Threaded, marked "IMC", lighter than RMC
RMC	344	Galvanized steel, aluminum or stainless	Threaded couplings	Threaded, heaviest wall
PVC Sch 40 / Sch 80	352	Rigid PVC	Solvent-cement couplings and bells	Gray, printed schedule; Sch 80 has a thicker wall
ENT	362	Corrugated PVC	Snap-in or cemented fittings	Pliable corrugated tubing, often blue
FMC	348	Interlocked steel or aluminum	Screw-in or clamp connectors	Bare spiral metal ("Greenfield")
LFMC	350	Metal core with PVC jacket	Liquidtight connectors	Jacketed metal spiral
LFNC	356	Nonmetallic	Nonmetallic liquidtight connectors	All-plastic flexible conduit

Key points

Trade size and metric designator (NEC 300.1(C)): 1/2 = 16, 3/4 = 21, 1 = 27, 1-1/4 = 35, 1-1/2 = 41, 2 = 53, 2-1/2 = 63, 3 = 78, 3-1/2 = 91, 4 = 103.
Trade size is a name, not a measured diameter. Do not size conduit with a tape measure alone. Compare it to a known fitting or read the marking.
EMT fittings do not fit IMC or RMC, because the ODs differ. IMC and RMC share the same thread form.
Some manufacturers sell colored EMT for identifying systems. The color is a product option, not a separate conduit type.

Common mistakes

Calling all metal conduit "rigid".
Selling indoor set-screw EMT fittings for a wet location where raintight compression fittings are needed.
Assuming flexible metal conduit is an acceptable equipment grounding path for any length or size. Check NEC 348.60 and 350.60.

Governing standards: NEC (NFPA 70) Articles 342, 344, 348, 350, 352, 356, 358 and 362, and NEC 300.1(C); UL 6, UL 1242, UL 797, UL 651; ANSI C80.1, C80.3, C80.6.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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