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NEC Article 314.16(B)Worked ExampleElectrical

NEC Box Fill Calculation: Six 12 AWG, Internal Clamps, One Device

Calculate minimum metal device box cubic inch volume for six 12 AWG conductors, internal clamps, and one duplex receptacle under NEC 314.16.

Direct Answer
22.50 cu. in. Minimum Box Volume (e.g., 4 x 4 x 1-1/2 square box with plaster ring)

Calculated strictly in accordance with NEC Article 314.16(B).

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Given Scenario Parameters

conductors1 conductors
conduit TypeBox Fill

Interactive Calculator (Pre-filled)

Adjust inputs to evaluate variations of this NEC code scenario.

Conduit Cross-Section CAD Blueprint

Trade Size: 1/2″ EMT

SAFE CODE CAPACITY
123456Fill: 26.25% (NEC Max 40%)Wire Area: 0.0798 in² / Total Area: 0.304 in²
Conductors: 6 Total
Conduit Size1/2″ EMT
Fill Area0.0798 in²
Fill %26.25%
01

Conduit & Wire Schedule

Quick Presets:
Conductor Wire List (6 Wires)
Conduit Sizing Schedule & Trade Size
26.3% Fill (Limit 40%)
Recommended Trade Size
1/2EMT
6 Conductors • Total Wire Area: 0.0798 sq in
Raceway Fill Telemetry
Conduit Internal Area:0.3040 sq in
Max Code Fill Capacity:40%
Actual Fill Utilization:26.3%

Step-by-Step Solution

Formal engineering derivation citing applicable National Electrical Code articles.

Governing Code Equation
Volume = Sum of Volume Allowances * 2.25 cu in
Citing NEC Article 314.16(B)
1

Conductor volume factor for 12 AWG per NEC Table 314.16(B) = 2.25 cu. in. per conductor.

2

Count conductors: 6 circuit wires = 6 volume units.

3

Internal cable clamps: Add 1 volume unit for one or more internal cable clamps.

4

Duplex receptacle device: Add 2 volume units for device strap.

5

Equipment grounding wire: Add 1 volume unit for grounding conductors.

6

Total volume units = 6 + 1 + 2 + 1 = 10 units.

7

Total box volume required: 10 * 2.25 cu. in. = 22.50 cubic inches.

Conclusion: 22.50 cu. in. Minimum Box Volume (e.g., 4 x 4 x 1-1/2 square box with plaster ring)
NEC Article 314.16(B)