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Octagon Box 2-1/8" Deep

Deep octagon box for ceiling installations requiring more conductor capacity.

21.5

cu.in. Volume

10

Max 14 AWG

9

Max 12 AWG

4" Octagon x 2-1/8"

Dimensions

Conductor Capacity per NEC 314.16

Maximum number of conductors that can fit in this 21.5 cu.in. box based on wire gauge (not accounting for devices, clamps, or grounds).

Wire GaugeVolume EachMax Conductors*
18 AWG1.5 cu.in.14
16 AWG1.75 cu.in.12
14 AWG2 cu.in.10
12 AWG2.25 cu.in.9
10 AWG2.5 cu.in.8
8 AWG3 cu.in.7
6 AWG5 cu.in.4

*Theoretical maximum for conductors only. Actual capacity will be less when including devices, clamps, and grounding conductors.

Common Applications

Heavy ceiling fixtures
Ceiling fans
Multiple circuits

Calculate Box Fill for Octagon Box 2-1/8" Deep

Use our free calculator to verify your Octagon Box 2-1/8" Deep meets NEC 314.16 requirements.

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Similar Box Types

4" Square x 1-1/4" Deep

4" x 4" x 1-1/4" • 18 cu.in.

4" Square x 1-1/2" Deep

4" x 4" x 1-1/2" • 21 cu.in.

4" Square x 2-1/8" Deep

4" x 4" x 2-1/8" • 30.3 cu.in.

4-11/16" Square x 1-1/4" Deep

4-11/16" x 4-11/16" x 1-1/4" • 25.5 cu.in.

About the Octagon Box 2-1/8" Deep

The Octagon Box 2-1/8" Deep provides 21.5 cubic inches of volume for electrical connections. This metal box is commonly used for heavy ceiling fixtures, ceiling fans, multiple circuits. With dimensions of 4" Octagon x 2-1/8", it offers adequate space for most residential and light commercial applications.

Box Fill Calculation Example

For a typical installation using 14 AWG conductors:

  • Box volume: 21.5 cu.in.
  • 14 AWG conductor volume: 2.00 cu.in. each
  • Maximum conductors (theoretical): 10

Remember to account for devices (2× conductor volume each), internal clamps (1× conductor volume), and equipment grounding conductors (1× conductor volume for all grounds combined).

Practical Example: Receptacle Installation

Installing a duplex receptacle with two 14/2 NM cables in this box:

  • 4 × 14 AWG conductors = 4 × 2.00 = 8.00 cu.in.
  • 2 × grounds (count as 1) = 1 × 2.00 = 2.00 cu.in.
  • Internal clamps = 1 × 2.00 = 2.00 cu.in.
  • 1 × receptacle = 2 × 2.00 = 4.00 cu.in.
  • Total: 16.00 cu.in.

Result: 16.00 cu.in. ≤ 21.5 cu.in. = COMPLIANT

Related Resources

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