Side-by-Side Comparison
Electrical & Wiring
Electrical Boxes vs. Wire Ampacity Ratings
Comparing 2 standards across 20 specifications. 20 key differences identified.
Comparing:
Electrical Boxes
Wire Ampacity Ratings
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).
National Electrical Code (NEC) Table 310.16 establishes allowable conductor ampacities based on conductor material (Copper vs Aluminum), ambient temperature, and insulation thermal ratings (60°C TW/NM-B Romex, 75°C THWN, 90°C THHN).
Specification Comparison Table
20 Parameters| Parameter / Spec | ||
|---|---|---|
|
Governing Standards
|
NEMA OS 1 / NEC Article 314.16 | — |
|
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 | — |
|
Governing Code
|
— | NFPA 70: National Electrical Code (NEC) Table 310.16 |
|
Small Conductor Overcurrent Rule (NEC 240.4D)
|
— | 14 AWG Cu: Max 15A | 12 AWG Cu: Max 20A | 10 AWG Cu: Max 30A |
|
14 AWG Copper (NM-B / Romex)
|
— | 15 Amps (60°C column applied per NEC 334.80) |
|
12 AWG Copper (NM-B / Romex)
|
— | 20 Amps (Standard residential branch circuit) |
|
10 AWG Copper (NM-B / Romex)
|
— | 30 Amps (Clothes dryers, 30A water heaters) |
|
8 AWG Copper (75°C THWN / NM-B)
|
— | 40A (NM-B 60°C) / 50A (THWN 75°C conduit) |
|
6 AWG Copper (75°C THWN / NM-B)
|
— | 55A (NM-B 60°C) / 65A (THWN 75°C conduit) |
|
4 AWG Copper (75°C THWN)
|
— | 85 Amps (Residential subpanel feeder) |
|
2 AWG Copper (75°C THWN)
|
— | 115 Amps (100A subpanel / main feeder) |
|
4/0 Aluminum (75°C XHHW / SE)
|
— | 180 Amps under standard NEC Table 310.16 ampacity; commonly used as the minimum conductor for a 200A dwelling service under NEC's separate service-conductor allowance (Table 310.12, formerly 310.15(B)(7)) |