Side-by-Side Comparison
Electrical & Wiring
Electrical Conduit Fill Capacity vs. Electrical Boxes
Comparing 2 standards across 17 specifications. 17 key differences identified.
Comparing:
Electrical Conduit Fill Capacity
Electrical Boxes
Electrical conduit fill capacity is strictly regulated under the National Electrical Code (NEC Chapter 9, Tables 1, 4, and 5) limiting total conductor cross-sectional area to 40% of internal conduit area for three or more wires, preventing heat buildup and insulation damage during wire pulls.
Standard electrical outlet and junction boxes are specified by trade dimensions and minimum internal cubic inch volume, including 4-inch square boxes (1900/1920 boxes, 21.0–30.3 cu in), 4-inch octagon ceiling boxes (15.5–21.5 cu in), and single-gang device boxes (18.0 cu in).
Specification Comparison Table
17 Parameters| Parameter / Spec | ||
|---|---|---|
|
Governing Standards
|
NFPA 70 (NEC) Chapter 9 / Annex C (Conduit Fill Tables) / NEMA Standards | NEMA OS 1 / NEC Article 314.16 |
|
The NEC 40% Fill Rule
|
1 Conductor: 53% max | 2 Conductors: 31% max | 3 or More Conductors: 40% max cross-sectional fill | — |
|
1/2" EMT Conduit (Trade Size 16)
|
Internal Area: 0.304 sq in | 40% Fill: 0.122 sq in | Max 9× 14 AWG, 6× 12 AWG, or 4× 10 AWG THHN wires | — |
|
3/4" EMT Conduit (Trade Size 21)
|
Internal Area: 0.533 sq in | 40% Fill: 0.213 sq in | Max 16× 14 AWG, 10× 12 AWG, or 7× 10 AWG THHN wires | — |
|
1" EMT Conduit (Trade Size 27)
|
Internal Area: 0.864 sq in | 40% Fill: 0.346 sq in | Max 26× 14 AWG, 16× 12 AWG, or 12× 10 AWG THHN wires | — |
|
1-1/4" EMT Conduit
|
Internal Area: 1.496 sq in | 40% Fill: 0.598 sq in | Ideal for 100A subpanel feeds (3× 1 AWG + 6 AWG ground) | — |
|
2" EMT Conduit
|
Internal Area: 3.356 sq in | 40% Fill: 1.342 sq in | Standard 200A residential service mast (3× 2/0 Cu or 4/0 Al) | — |
|
Conduit Types
|
EMT (Electrical Metallic Tubing), Schedule 40 PVC, Schedule 80 PVC (Thick wall), Rigid Metal (RMC) | — |
|
4" Square Box (1-1/2" Deep–1900 Box)
|
— | 4.0 × 4.0 × 1.5 in (102 × 102 × 38 mm) | 21.0 cu in (344 cm³) |
|
4" Square Box (2-1/8" Deep–1920 Box)
|
— | 4.0 × 4.0 × 2.125 in (102 × 102 × 54 mm) | 30.3 cu in (496 cm³) |
|
4" Octagon / Round Ceiling Box
|
— | 4.0 × 4.0 × 1.5 in (102 × 102 × 38 mm) | 15.5 to 21.5 cu in |
|
Handy / Utility Box (Surface 2×4")
|
— | 4.0 × 2.125 × 1.875 in | 13.0 to 14.5 cu in |
|
Single-Gang Plastic Device Box
|
— | Standard 18.0 to 22.5 cu in (supports up to 9 × 14 AWG conductors) |
|
Double-Gang Plastic Device Box
|
— | Standard 32.0 to 35.0 cu in |
|
Volume Allowance per 14 AWG Conductor
|
— | 2.00 cu in (32.8 cm³) per wire |
|
Volume Allowance per 12 AWG Conductor
|
— | 2.25 cu in (36.9 cm³) per wire |
|
Volume Allowance per 10 AWG Conductor
|
— | 2.50 cu in (41.0 cm³) per wire |
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