30 CFR § 18.50 - Protection against external arcs and sparks.
---
identifier: "/us/cfr/t30/s18.50"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "30 CFR § 18.50 - Protection against external arcs and sparks."
title_number: 30
title_name: "Mineral Resources"
section_number: "18.50"
section_name: "Protection against external arcs and sparks."
chapter_name: "MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR"
subchapter_number: "B"
subchapter_name: "TESTING, EVALUATION, AND APPROVAL OF MINING PRODUCTS"
part_number: "18"
part_name: "ELECTRIC MOTOR-DRIVEN MINE EQUIPMENT AND ACCESSORIES"
positive_law: false
currency: "2026-04-05"
last_updated: "2026-04-05"
format_version: "1.1.0"
generator: "[email protected]"
authority: "30 U.S.C. 957, 961."
regulatory_source: "33 FR 4660, Mar. 19, 1968, unless otherwise noted."
cfr_part: "18"
---
# 18.50 Protection against external arcs and sparks.
Provision shall be made for maintaining the frames of all off-track machines and the enclosures of related detached components at safe voltages by using one or a combination of the following:
(a) A separate conductor(s) in the portable cable in addition to the power conductors by which the machine frame can be connected to an acceptable grounding medium, and a separate conductor in all cables connecting related components not on a common chassis. The cross-sectional area of the additional conductor(s) shall not be less than 50 percent of that of one power conductor unless a ground-fault tripping relay is used, in which case the minimum size may be No. 8 (AWG). Cables smaller than No. 6 (AWG) shall have an additional conductor(s) of the same size as one power conductor.
(b) A means of actuating a circuit-interrupting device, preferably at the outby end of the portable cable.
The frame to ground potential shall not exceed 40 volts.
(c) A device(s) such as a diode(s) of adequate peak inverse voltage rating and current-carrying capacity to conduct possible fault current through the grounded power conductor. Diode installations shall include: (1) An overcurrent device in series with the diode, the contacts of which are in the machine's control circuit; and (2) a blocking diode in the control circuit to prevent operation of the machine with the polarity reversed.