314.16(B)(6) Terminal Block Fill.

A terminal block in a box counts for a single volume allowance in accordance with Table 314.16(B)(1). This is for each terminal block assembly based on the largest conductor terminated to the assembly.
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A terminal block in a box counts for a single volume allowance in accordance with Table 314.16(B)(1). This is for each terminal block assembly based on the largest conductor terminated to the assembly.

Code Change Summary: New code section on terminal block volume in a box.

Terminal blocks are not typically used in outlet or device boxes but when they are, they can occupy a lot of space.

Terminal blocks are different than typical wire splicing devices such as a wire nut since wire nuts are intended for single-polarity connections whereas terminal blocks have no such restriction and are often used to terminate several conductors, often having different polarity.

In the 2023 NEC®, a public input was accepted to ensure that a terminal block assembly is counted when calculating box fill. Where a terminal block is present in a box, new Section 314.16(B)(6) requires a single volume allowance in accordance with Table 314.16(B)(1) to be made for each terminal block assembly based on the largest conductor terminated to the terminal block assembly.

Most terminal blocks are not listed (certified by a Nationally Recognized Testing Laboratory) (NRTL) such as UL. Most terminal blocks are recognized components and do not have a stand-alone listing.

Recognized components are incomplete in certain constructional features or restricted in their performance capabilities and are intended to be used as components of complete equipment that is submitted to the NRTL for investigation rather than for direct separate field installation. Field installing recognized components often results in the electrical inspector requiring a field evaluation of the complete installation which can be costly for the electrician.

Below is a preview of the NEC®. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2023 NEC® edition of NFPA 70.

2020 Code Language:

This code section did not exist.

2023 Code Language:

N 314.16(B)(6) Terminal Block Fill. Where a terminal block is present in a box, a single volume allowance in accordance with Table 314.16(B)(1) shall be made for each terminal block assembly based on the largest conductor(s) terminated to the assembly.

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314.16(B)(6) Terminal Block Fill.

Below is a Real Question from our Electrical Continuing Education Courses for Electrical License Renewal:

Based on the 2023 NEC, which of the following is true?

A: Each terminal block assembly counts as a single volume allowance in accordance with Table 314.16(B)(1), based on the largest conductor terminated to the terminal block assembly.
B: Each terminal block assembly counts as 2 volume allowances based on the largest conductor terminated to the terminal block assembly.
C: Each terminal block assembly counts as 3 volume allowances based on the largest conductor terminated to the terminal block assembly.
D: Each terminal block assembly counts as 4 volume allowances based on the largest conductor terminated to the terminal block assembly.
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