Raceway Types Compared (RMC, IMC, EMT, FMC, LFMC, PVC)
Summary: This guide compares RMC, IMC, EMT, FMC, LFMC, and PVC in NEC 2017—where each is used, grounding, fittings, support, bending, and tips.
1) Quick Reference Table
| Raceway | Material | Typical UL | Dry/Damp/Wet | Grounding Path | Fittings | Common Use |
|---|---|---|---|---|---|---|
| RMC (Art. 344) | Steel/stainless/aluminum | UL 6 | All (with coatings) | Yes* | Threaded | Harsh/industrial, services |
| IMC (Art. 342) | Steel | UL 1242 | All | Yes* | Threaded | RMC-like with less weight |
| EMT (Art. 358) | Steel/aluminum | UL 797 | Dry/damp/wet (listed fittings) | Yes* | Compression/set-screw | Commercial interiors |
| FMC (Art. 348) | Flexible metal | UL 1 | Primarily dry | Limited* | FMC connectors | Short whips, vibration |
| LFMC (Art. 350) | Liquidtight flex metal | UL 360 | Dry/damp/wet | Limited* | Liquidtight connectors | Outdoor equipment |
| PVC (Art. 352) | Nonmetallic | UL 651 | Dry/damp/wet/corrosive | EGC required | Solvent-cement | Underground, coastal |
2) Overview by Article (NEC 2017)
- Art. 342 — IMC: Intermediate Metal Conduit.
- Art. 344 — RMC: Rigid Metal Conduit.
- Art. 358 — EMT: Electrical Metallic Tubing.
- Art. 348 — FMC: Flexible Metal Conduit.
- Art. 350 — LFMC: Liquidtight Flexible Metal Conduit.
- Art. 352 — PVC: Rigid Polyvinyl Chloride Conduit.
3) Grounding & Bonding (EGC)
Metal raceways (RMC/IMC/EMT) can serve as the equipment grounding conductor when continuous and with listed fittings.
Flexible systems (FMC/LFMC) may need a separate EGC for reliable fault current return. PVC requires an EGC.
4) Securing & Supporting
Secure near boxes and at regular intervals as specified in each Article (e.g., 342.30, 344.30, 348.30, 350.30, 352.30, 358.30).
Size, orientation, and occupancy affect spacing and exceptions—verify the exact clause before installation.
5) Bending, Threads & Fittings
- RMC/IMC: Field thread/cut; use sealing fittings where required in hazardous locations.
- EMT: Hand/machine bends; use listed fittings rated for environment.
- FMC/LFMC: Maintain minimum bend radius; avoid excessive torsion.
- PVC: Solvent-cement; heat-bend per manufacturer; provide expansion fittings for thermal movement.
6) Field Applications & Tips
- Use coated RMC/IMC or PVC in corrosive/coastal environments; bond transitions.
- LFMC is common at rooftop equipment; check UV/sunlight and temperature ratings.
- EMT is typical for protected commercial interiors; ensure fittings are listed for any wet areas.
- PVC is prevalent underground; follow burial and backfill requirements and add expansion couplings for long runs.
7) FAQ
Q1: Can EMT be used outdoors?
A: Yes—if the EMT and fittings are listed for wet/corrosive exposure.
Q2: Do I need a separate EGC with FMC/LFMC?
A: Often yes; check the specific limits and install a separate EGC as needed.
Q3: Does PVC need expansion fittings?
A: For long exterior runs or large temperature swings, yes—per manufacturer and Art. 352 guidance.