Conduit Reference
Types of Electrical Conduit
Every common conduit type, the NEC article that governs it, where it is allowed, and a full fill matrix so you can see at a glance how many wires each holds.
Internal areas from NEC Chapter 9 Table 4; fill limit from Table 1; article numbers from NEC Chapter 3. NFPA 70 2023. Confirm your AHJ’s adopted edition and any local amendments.
The Conduit Types, With Their NEC Articles
| Type | Name | NEC Article | Best for | Locations |
|---|---|---|---|---|
| EMT | Electrical Metallic Tubing | Art. 358 | Dry, exposed indoor and commercial runs | Dry; wet with listed raintight fittings; direct burial with identified fittings and corrosion protection; not where subject to severe physical damage |
| IMC | Intermediate Metal Conduit | Art. 342 | Physical protection, outdoors, hazardous locations; lighter than RMC | All, including wet, underground, and hazardous (with corrosion protection) |
| RMC | Rigid Metal Conduit | Art. 344 | Maximum mechanical protection and hazardous locations | All, including wet, underground, and hazardous (with corrosion protection) |
| PVC | Rigid PVC Conduit (Schedule 40 / 80) | Art. 352 | Wet, underground, and corrosive locations; needs a pulled EGC | Wet, underground, corrosive; Schedule 80 where exposed to physical damage |
| ENT | Electrical Nonmetallic Tubing | Art. 362 | Concealed in walls, floors, and ceilings; concrete-encased | Concealed or protected; not for exposed severe-damage or most plenum uses |
| FMC | Flexible Metal Conduit | Art. 348 | Short connections to motors and fixtures where flexibility is needed | Dry locations; not where liquids are present unless liquidtight |
| LFMC | Liquidtight Flexible Metal Conduit | Art. 350 | Flexible connections in wet or oily areas, outdoor equipment, HVAC | Wet locations; direct burial where listed |
| LFNC | Liquidtight Flexible Nonmetallic Conduit | Art. 356 | Flexible, corrosion-resistant connections in wet locations | Wet and corrosive; needs a pulled EGC |
Conduit Fill by Type: #12 THHN Matrix
How many #12 THHN conductors each conduit type holds at the NEC 40 percent fill limit, every trade size side by side. The pattern holds for other conductor sizes: IMC is roomiest, Schedule 80 PVC tightest, because the ranking is set by each type’s internal area.
| Trade size | EMT | IMC | RMC | PVC-40 | PVC-80 | ENT |
|---|---|---|---|---|---|---|
| 1/2" | 9 | 10 | 9 | 8 | 6 | 7 |
| 3/4" | 16 | 17 | 16 | 15 | 12 | 13 |
| 1" | 25 | 28 | 26 | 25 | 20 | 23 |
| 1-1/4" | 44 | 49 | 45 | 43 | 37 | 42 |
| 1-1/2" | 61 | 66 | 62 | 59 | 51 | 58 |
| 2" | 100 | 109 | 102 | 98 | 86 | 96 |
| 2-1/2" | 176 | 154 | 146 | 141 | 123 | — |
| 3" | 266 | 238 | 225 | 218 | 193 | — |
| 3-1/2" | 347 | 318 | 301 | 292 | 261 | — |
| 4" | 443 | 409 | 387 | 377 | 338 | — |
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Frequently Asked Questions
What are the main types of electrical conduit?
The common types split into rigid metal, rigid nonmetallic, and flexible. Rigid metal is EMT (thin-wall steel, NEC Article 358), IMC (intermediate, Article 342), and RMC (heaviest, Article 344). Rigid nonmetallic is PVC (Article 352). Flexible types are ENT (nonmetallic tubing, Article 362), FMC (flexible metal, Article 348), LFMC (liquidtight flexible metal, Article 350), and LFNC (liquidtight flexible nonmetallic, Article 356). Each has its own NEC article that governs where and how it may be used.
Which conduit holds the most wires for its size?
Of the rigid types, IMC has the largest internal area for a given trade size, so it holds the most conductors, followed by EMT and RMC, with Schedule 40 PVC smaller and Schedule 80 PVC smallest because its thicker wall shrinks the inside. The difference is real but modest: at 3/4 inch, IMC holds a couple more #12 THHN than Schedule 80 PVC. The full matrix on this page shows every trade size at the NEC 40 percent fill limit.
What is the difference between EMT, IMC, and RMC?
All three are steel, but the wall thickness and how you join them differ. EMT is thin-wall and uses set-screw or compression fittings, no threads, and is bent with a hand bender. IMC and RMC are threaded rigid conduit: IMC has a thinner wall than RMC, so it is lighter, cheaper, and roomier inside, while RMC is the heaviest and most robust. EMT is the everyday choice for dry exposed runs; IMC and RMC are used where physical protection or a hazardous-location rating is required, with IMC usually preferred for its lower weight.
Which conduit is used for underground and wet locations?
PVC (Schedule 40 for most direct burial, Schedule 80 where physical damage is a concern) is the usual underground and wet-location choice because it does not corrode. RMC and IMC are also permitted underground and outdoors, typically where extra strength is needed, with corrosion protection. The 2023 NEC also permits EMT for direct burial with fittings identified for the purpose and proper corrosion protection, though PVC and rigid metal remain the practical choices underground. For flexible connections in wet areas, use LFMC or LFNC, the liquidtight types. Always follow the NEC 300.5 burial depths for the wiring method you choose.
Related Tools
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Max THHN per size from #14 to 500 kcmil in one EMT reference table.
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Pick the type, then run the fill.
Once you know which conduit the job calls for, the fill calculator gives the exact conductor count for any size and mix, straight from NEC Chapter 9.