ENT Conduit Fill Chart
Electrical nonmetallic tubing (Smurf tube) wire capacity, computed from NEC 2023 Chapter 9 Tables 1, 4 and 5.
This is the complete ENT wire fill chart, computed live from NEC 2023 Chapter 9 Tables 4 and 5. Choose an insulation, filter by wire size, then export as CSV or print. For a raceway carrying several conductor sizes, use the interactive conduit fill calculator.
- 1/2" ENT8 wires
- 3/4" ENT15 wires
- 1" ENT25 wires
- 1-1/4" ENT43 wires
- 1-1/2" ENT59 wires
- 2" ENT99 wires
| TRADE → WIRE ↓ | 1/2" | 3/4" | 1" | 1-1/4" | 1-1/2" | 2" |
|---|---|---|---|---|---|---|
| 14 AWG | 11 | 21 | 34 | 60 | 82 | 135 |
| 12 AWG | 8 | 15 | 25 | 43 | 59 | 99 |
| 10 AWG | 5 | 9 | 15 | 27 | 37 | 62 |
| 8 AWG | 3 | 5 | 9 | 16 | 21 | 36 |
| 6 AWG | — | 4 | 6 | 11 | 15 | 26 |
| 4 AWG | — | 2 | 4 | 7 | 9 | 16 |
| 3 AWG | 1 | — | 3 | 6 | 8 | 13 |
| 2 AWG | 1 | — | 3 | 5 | 7 | 11 |
| 1 AWG | 1 | 1 | — | 3 | 5 | 8 |
| 1/0 | 1 | 1 | — | 3 | 4 | 7 |
| 2/0 | — | 1 | — | 2 | 3 | 6 |
| 3/0 | — | 1 | 1 | — | 3 | 5 |
| 4/0 | — | 1 | 1 | — | 2 | 4 |
| 250 | — | — | 1 | — | — | 3 |
| 300 | — | — | 1 | 1 | — | 3 |
| 350 | — | — | 1 | 1 | — | 2 |
| 400 | — | — | — | 1 | 1 | — |
| 500 | — | — | — | 1 | 1 | — |
| 600 | — | — | — | 1 | 1 | — |
| 700 | — | — | — | — | 1 | 1 |
| 750 | — | — | — | — | 1 | 1 |
| 800 | — | — | — | — | 1 | 1 |
| 900 | — | — | — | — | 1 | 1 |
| 1000 | — | — | — | — | — | 1 |
ENT — Electrical Nonmetallic Tubing × THHN (90°C dry) · NEC 2023 Ch.9 Tables 4 & 5 · 40% (3+), 31% (2), 53% (1)
NOTES & CONTEXT
How to use the ENT fill chart
Each row is a trade size of electrical nonmetallic tubing. Interior cross-sectional areas come from NEC 2023 Chapter 9 Table 4 and conductor areas from Table 5. NEC Chapter 9 Table 1 fixes the allowable fill: 53 % for a single conductor, 31 % for exactly two, and 40 % for three or more. ENT is tabulated only through 2 in, so the chart stops there.
What is ENT?
ENT is electrical nonmetallic tubing under NEC Article 362 — the corrugated blue raceway most electricians simply call “Smurf tube.” It is a pliable, corrugated, nonmetallic tube that bends by hand without tools, uses solvent-cement or snap fittings, and is popular for its speed of installation. Because it is nonmetallic it needs a separate equipment grounding conductor pulled with the circuit.
Where ENT is allowed and its use limits
ENT is common inside concrete slabs, inside masonry and stud walls, and above suspended ceilings used as a return-air plenum only where specifically listed. NEC 362.10 and 362.12 spell out where it may and may not go: it is generally required to be concealed, is restricted in buildings exceeding certain height thresholds unless encased in concrete, and is not permitted in areas of physical damage or in direct sunlight unless listed for it. Its corrugated wall gives it a smaller interior than a smooth raceway of the same trade size. For flexible metal alternatives, see the flexible conduit fill chart.
Common ENT scenarios
- Homeruns embedded in a poured concrete floor slab before the pour.
- Branch circuits fished inside stud walls in residential and light commercial work.
- Feeds concealed above accessible ceilings on a fast-track tenant build-out.
- Wall stub-ups from a slab to device boxes, cemented into a smooth transition coupling.
Reading the fill limits
ENT uses the standard NEC Chapter 9 Table 1 fill: 53 % for one conductor, 31 % for two, and 40 % for three or more. Because the wall is corrugated, ENT's interior at a given trade size is smaller than a smooth-wall raceway such as EMT, so the same conductor bundle may need a larger ENT trade size. The corrugations also add friction on a long pull, which is another practical reason to stay comfortably under the 40 % ceiling rather than fill to the exact limit.
Grounding in ENT
ENT is nonmetallic and cannot serve as an equipment ground, so NEC 362 requires a separate equipment grounding conductor with every circuit. That conductor is part of the fill total and must be counted before you check the chart. On a typical three-wire branch circuit with ground, you are filling for four conductors and applying the 40 % column. Leaving the ground out of the count is the most common way an ENT run ends up over the Table 1 limit.
Heat de-rating note
This is a fill chart, not an ampacity chart: it tells you how many conductors physically fit under NEC Chapter 9, not the current they may carry. When more than three current-carrying conductors share the tubing, apply NEC 310.15(C)(1): 80 % ampacity for 4 to 6, 70 % for 7 to 9, and 50 % for 10 to 20 current-carrying conductors. Conductors installed in concrete or below grade can also see the raceway treated as a wet location, which affects insulation choice and may push you toward a wet-rated type such as THWN-2. The chart shown here assumes every conductor is 12 AWG THHN; changing size or insulation changes the Table 5 area and therefore the count in every row. Check your specific conductor mix in the conduit fill calculator before ordering.