30 CFR § 7.305 - Critical characteristics.

---
identifier: "/us/cfr/t30/s7.305"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "30 CFR § 7.305 - Critical characteristics."
title_number: 30
title_name: "Mineral Resources"
section_number: "7.305"
section_name: "Critical characteristics."
chapter_name: "MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR"
subchapter_number: "B"
subchapter_name: "TESTING, EVALUATION, AND APPROVAL OF MINING PRODUCTS"
part_number: "7"
part_name: "TESTING BY APPLICANT OR THIRD PARTY"
positive_law: false
currency: "2026-03-24"
last_updated: "2026-03-24"
format_version: "1.1.0"
generator: "[email protected]"
authority: "30 U.S.C. 957."
regulatory_source: "53 FR 23500, June 22, 1988, unless otherwise noted."
cfr_part: "7"
---


# 7.305 Critical characteristics.

The following critical characteristics shall be inspected on each motor assembly to which an approval marking is affixed:

(a) Finish, width, and planarity of surfaces that form any part of a flame-arresting path.

(b) Clearances between mating parts that form flame-arresting paths.

(c) Thickness of walls, flanges, and covers that are essential in maintaining the explosion-proof integrity of the enclosure.

(d) Spacing of fastenings.

(e) Length of thread engagement on fastenings and threaded parts that assure the explosion-proof integrity of the enclosure.

(f) Use of lockwasher or equivalent with all fastenings.

(g) Dimensions which affect compliance with the requirements for packing gland parts in § 7.304 of this part.