Box Fill Room
Box fill is a counting exercise tied to Article 314.16. Each conductor, each clamp group, each support, each device yoke, and all grounds get counted, then multiplied by the volume for the largest conductor present. Miss the device count of two or the single ground count and the whole answer moves. Count clean and it holds.
Last reviewed June 2026 · Staff Answer
In a box-fill count, how many conductors does a single device yoke count as?
Pick an answer to see the work and why each wrong choice traps people.
What this room is for
- Counting conductors, clamps, supports, devices, and grounds correctly
- Using the largest conductor volume for the multipliers
- Catching the device-yoke count of two
What not to post
- Asking for quoted 314.16 text. Cite the article and table.
- Posting real exam questions.
- Sharing anything that identifies you.
Answered questions in this room
How do I count devices and grounds for box fill?
A device or yoke counts as two, at the volume of the largest conductor connected to it. All the equipment grounding conductors together count as one, also at the largest ground volume. Those two rules trip up most people. Count each as a unit, multiply by the right volume, and the box fill holds.
What are the steps to calculate box fill?
Count five things, then multiply. Each conductor entering the box counts once, each clamp group counts once, each support fitting counts once, each device yoke counts twice, and all grounds together count once. Multiply that total count by the volume for the largest conductor present from Table 314.16(B), then compare to the box volume.
Room FAQ
What is the Box Fill Room?
Box fill is a counting exercise tied to Article 314.16. Each conductor, each clamp group, each support, each device yoke, and all grounds get counted, then multiplied by the volume for the largest conductor present. Miss the device count of two or the single ground count and the whole answer moves. Count clean and it holds.
What should I do first in this room?
Start with the daily drill. Pick an answer before reading the explanation, then read why the wrong choices trap candidates.
When should I take the full diagnostic?
Take the full diagnostic when you are not sure which NEC area is costing you points, or when the same miss shows up more than once.
Discussions
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Quick back-and-forth with others studying this room. You post under a pseudonym. Be straight, cite article numbers, never copied code.
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