PART 18-JUNCTION BOXES AND ELECTRIC MOTOR-DRIVEN MINE EQUIPMENT

Sec. 18.2

Conditions under which approvals may be granted. [Amended] 18.3 Detailed requirements for Class 1 parts. [Amended]

18.6 Character of tests. [Amended] 18.7 Inspection and test of parts supplied by other manufacturers. [Revised] AUTHORITY: §§ 18.2 to 18.7, appearing in this Supplement, issued under 37 Stat. 681, as amended; 30 U.S.C. 3.

SOURCE: §§ 18.2 to 18.7, appearing in this Supplement, contained in Regulation, Director, Bureau of Mines, approved by the Assistant Secretary of the Interior, effective Oct. 21, 1947, 12 F.R. 7285.

(4) Drawings and specifications required. The Bureau will not undertake the inspection and test of equipment until a set of legible drawings, bill of material, and specifications sufficient in number and detail to identify the parts fully have been delivered to the Supervising Engineer, Electrical-Mechanical Section, at the Central Experiment Station. The nature of the drawings and specifications required is described in subsequent paragraphs of this section. No drawings or specifications should be sent to the Washington Office of the Bureau. Drawings should be numbered and dated to facilitate identification and reference in records. The complete rating of each motor shall be specified, and the capacity of all fuses and the setting of overload protective devices shall be given. All drawings are to be handled as strictly confidential by the Bureau.

The set of drawings shall include the following: [Introductory text amended]

(ii) A drawing or drawings that shall specify the material and detailed dimensions of all parts that make up explosionproof enclosures for units included under Class I, § 18.2 (b) (1), also of those parts that form any portion of the joints through which possible flames might escape. Upon request, the manufacturer shall specify the material and dimensions for such other parts as the Bureau considers necessary for proper record. [Subdivision (ii) amended]

(b) If full detailed dimensions are not given for all parts, this drawing (or drawings) may show the assembled motor in section, Provided, The section or sections show the parts in their correct proportions and location with respect to each other. A skeleton drawing shall not cover more than one motor-frame diameter. It is recommended that information covering the ratings, range of voltages, speeds, and frequencies for which the motor will be available in this frame be included on the skeleton drawing. Each frame shall have a suitable designation for purposes of reference and identification. [Inferior subdivision (b) amended]

(b) General requirements. (8) Grounding.

When the grounding conductor is one of several making up a portable cable or a connecting cable, the size (cross-sectional area) of the grounding conductor (or conductors) shall be determined in accordance with the following:

(i) If the size of the power conductor is No. 6 or larger, the cross-sectional area of the grounding conductor shall not be less than 50 percent of that of the power conductor, except that in no case shall the grounding conductor be less than No. 8.

(ii) If the size of the power conductor is smaller than No. 6, the cross-sectional area of the grounding conductor shall not be less than that of the power conductor. [Subparagraph (8) amended]

(10) Portable cables. Every machine operated from an external source of power shall have a portable cable of adequate length and current-carrying capacity. This cable shall have an outer sheath of rubber or equivalent material that is highly resistant to abrasion, moisture, and flame. The cable shall meet the flame-resistance test outlined in § 18.6 (c). The conductors shall have high-grade insulation of rubber or its equivalent. The use of colored insulation or other suitable markers is recommended for identifying individual conductors to facilitate proper connections and splicing according to polarity. The number of conductors in the portable

cable should be kept to the minimum necessary for feasible operation of the machine.

Suitable provision shall be made to facilitate disconnection of portable cables quickly and conveniently for replacement. [First paragraph amended]

for

§ 18.3 Detailed requirements Class 1 parts—(a) Enclosure casings.

(2) Joints and machining tolerances.

The surfaces comprising a flange joint need not be all in one plane. For enclosures having an unoccupied volume (air space) of more than 60 cubic inches, the total width of joint measured along the shortest path from inside to outside of the enclosure shall not be less than 1 inch, except as follows: A rabbet joint having a total width of 3/4 inch may be 'accepted if neither the cylindrical nor the plane fit is less than inch wide. If the unoccupied volume (air space) is 60 cubic inches or less, a minimum width of 3/4 inch may be accepted for plane joints, but a 1-inch width of plane or rabbet joint is recommended. The diametrical clearance for cylindrical fits in rabbet joints shall not exceed 0.004 inch if the plane fit is less than 4 inch wide. If the plane fit is 1/4 inch or more in width, the diametrical clearance for cylindrical fits shall not exceed 0.008 inch. The edge of a rolled-steel plate forming part of an explosion-proof enclosure may be used as a plane flange, provided the width does not fall short of the previously specified flange widths by more than 64 inch. [Undesignated paragraph amended]

All

(7) Lead entrances. electrical conductors that pass through the walls of explosion-proof enclosures shall be provided with adequate insulation and guards at the point of entrance to the enclosure in accordance with one or more of the following:

(1) If stuffing-box lead entrances are used, the packing material shall be untreated asbestos, such as woven valvestem packing, and it shall be not less than 36 inch in diameter. The size and kind shall be specified on the drawings or bills of material. The amount of packing material in each stuffing box shall be such that, when compressed, it will completely surround the wire or cable

for not less than 1⁄2 inch measured along the wire or cable.

The stuffing-box design and the "amount of packing used shall be such that, with the packing properly compressed, the gland still has a clearance distance of 8 inch or more to travel without meeting interference by parts other than packing. The glands shall be secured against loosening. The use of insulating bushings in stuffing boxes is recommended, especially for voltages that exceed 250. When an outer braid insulation covering is used on wires and cables passing through stuffing boxes, it should be made of asbestos or slow-burning material.

The width of space for packing material shall not exceed the diameter or width of the uncompressed material by more than 50 percent. At other points small clearances shall be maintained between the stuffing-box parts and the cables or wires passing through them. A diametrical clearance greater than 146 inch will not be accepted if packing material less than 1/4-inch diameter is used. If untreated, woven packing material of 1/4-inch or greater nominal diameter is used, a diametrical clearance not greater than 8 inch will be accepted.

To minimize deviation from acceptable clearances in stuffing boxes, the cables used in them should conform to the following standardized dimensions:

Two-CONDUCTOR-ROUND CABLES

.. 51

(8) Distribution boxes.

Each branch circuit shall be plainly and permanently marked to show the maximum current that can be taken from it, and plugs that are not of identical rating shall be polarized or otherwise arranged to prevent inserting them in the wrong socket. [Fourth undesignated paragraph amended]

§ 18.6 Character of tests.

(c) Portable cable run-over test. The following run-over test has been established for determining the durability of portable cables for use with permissible equipment, and cables that pass this test will be listed for this service.

The cable will be placed across the two rails of a track, and a four-wheeled car of 7 tons gross weight will be run over it 50 times. The speed of the car shall be approximately 31⁄2 miles per hour, and potential shall be applied to the cable during tests. The cable will be shifted after each passage of the car, thus giving 100 places in the cable over which two wheels have passed. If the cable fails by short-circuiting or grounding to the rails or wheels at 11 or more places, it will not be listed by the Bureau. [Paragraph (c) amended]

(d) Portable cable flame-resistance test. The following test has been established for determining the flame-resistant properties of portable cables:

A 6-foot sample of the cable in the form of a closed U shall be mounted horizontally and heated electrically, using a current that is 500 percent of the following conductor ratings:

No. 6.

.77

No. 5.

.52 .80

Inches Inches Inches 0.81 0.91 0.99 +0.03 .93 1.01 1.10 +.03 1.01 1.10 1.19 .03

1.08 1.17 1.27 ±.03

1.17

1.24 1.34

66 .94

1.68 ±.03

1.79 ±.04

1.93 ±.04

No. 1/0.

.03

1.27 1.34 1.48 ±.03

1 With (type G) or without (type W) grounding conductors.

Corners shall be well-rounded at all points where cables and wires emerge from bushings, glands, and stuffing boxes to prevent cutting of insulation. Stuffing boxes, if not made integral with enclosures, shall be securely held to enclosures on which they are used.

the adjacent legs of the sample is 350° F. The flame of a Tirrill gas burner adjusted to give an over-all free flame height of 5 inches and a 3-inch inner cone shall be applied directly underneath the sample at a point 31⁄2 inches from the terminal ends of the sheath for 60 seconds, the top of the burner being 3 inches below the lower surface of the sample.

With the gas flame and heating current cut off simultaneously, burning of the sheath shall not spread over more than 14 inches of the folded sample.

At least 5 samples of a given cable will be tested to determine its resistance to flame. If 4 of the 5 samples pass this test, the cable will be listed as "flame resistant" and shall be suitably marked at intervals not exceeding 12 feet with an identifying number assigned by the Bureau of Mines. [Paragraph (d) added]

§ 18.7 Inspection and test of parts supplied by other manufacturers. All the accessory parts for an approved machine need not be made by the manufacturer requesting the approval. If parts are obtained from other manufacturers, these accessories may be submitted for inspection and test, either by the builder of the permissible machine or directly by the manufacturer of the accessory. All the requirements to be met under either option are identical. Application for such inspection and test by an accessory manufacturer shall be made by a letter addressed to the Director, Bureau of Mines, Washington, D. C., and shall be accompanied by the required fee (see § 18.2 (a) (3)). When the accessory has successfully met all the requirements the Bureau, upon request, will give the manufacturer thereof a letter stating that further test or inspection of the accessory will not be required if it is constructed in strict accordance with the specifications on file at the Bureau. This letter may be cited to the builder of the complete approved machine. Since the Bureau of Mines does not sanction the words "permissible" or "approved" except as applying to complete assemblies, advertising or labeling such accessories as permissible or approved by the Bureau will not be sanctioned. However, motors' may be advertised and labeled as

'Under this amendment, authorization to advertise and label motors will be limited to those motors which are not combined with switches, resistors, starters, or other auxiliary apparatus.

explosion-proof and suitable for use on permissible assemblies. Such label shall not be used without prior written authorization from the Director. Authorization will be granted only upon request addressed to the Director providing the conditions applying thereto have been met. The label shall contain the following: "Explosion-Proof Mine MotorBuilt to Bureau of Mines Schedule-Bureau of Mines File X/P ... ." The Bureau will assign an identifying file number in the letter authorizing the use of a label. The label can be in the form of a separate plate or else combined with the standard motor nameplate. A sample of the plate adopted shall be sent to the Supervising Engineer, ElectricalMechanical Section, at the Central Experiment Station in Pittsburgh, Pa. The Bureau reserves the right to rescind for cause, at any time, any authorization granted under this section.

AUTHORITY: §§ 25.0 to 25.1C, inclusive, issued under sec. 311, 47 Stat. 410; 30 U. S. C. 7; E. O. 6611, Feb. 22, 1934.

SOURCE: §§ 25.0 to 25.10, inclusive, contained in Regulations, Director, Bureau of Mines, approved by the Secretary of the Interior, effective Apr. 16, 1947, 12 F.R. 2650.

§ 25.0 Compliance with the requirements necessary for obtaining approval. To receive approval of the Bureau of Mines for any multiple-shot blasting units a manufacturer must comply with the requirements specified in this part.

§ 25.1 Purpose. The purpose of investigations under this part is to promote the development of suitable multipleshot blasting units for use under special conditions where the firing of several

shots, one at a time, may be considered less safe than firing all simultaneously. The sanction of the use of multiple-shot firing units, with capacities up to ten shots, does not rescind the general recommendation of this Bureau in favor of single-shot firing except under special conditions, and in no way modifies the safety principles prescribed by the Bureau for handling permissible explosives as published in Part 15 of this chapter. Lists of such units will be published from time to time for the information of State mine inspection departments, compensation bureaus, mine operators, miners, and others interested in safe equipment for mines. This part shall become effective when approved by the Secretary of the Interior.

Any blasting unit that meets the requirements set forth in this part will be termed "permissible" by the Bureau of Mines.

§ 25.2 Fees charged. (a) The fee for a complete investigation of a multipleshot blasting unit under this part is $100.1

(b) The fee for tests covering only a part of a complete investigation shall be proportional to the work involved.

Application for retests that may be equivalent to more than one-half of a complete investigation should be accompanied by a check for the full fee. Application for tests covering changes in design, which may require less than onehalf of a complete investigation, should be accompanied by a check for one-half of the full fee. Any surplus will be refunded at the close of the investigation.

(c) Under the present provisions of this part, extensions of approvals that do not require tests will be made without charge.

(d) Tests to assist a manufacturer in the development of his. device may be made upon request to the Director of the Bureau and will be charged for in amounts proportionate to the work involved.

1 Although the standard fee for a complete investigation is $100, the work involved in the investigation of a battery-type unit may not justify the full fee. In such cases a refund, depending upon the amount of work performed, but not exceeding $50, will be made.

§ 25.3 Instructions on making applications. A form of request for an investigation of a blasting unit follows: The Director of the Bureau of Mines, Department of the Interior, Washington 25, D. C.

Dear Sir:

We hereby make application for approval of the (type or model) Multiple-Shot Blasting Unit under the provisions of Schedule 16B. Attached is a certified check for one hundred dollars ($100) made payable to the Treasurer of the United States to cover the fee for the tests.

A copy of this application, one set of drawings, one complete unit, and a full set of instructions for operating are being sent to the Central Experiment Station, 4800 Forbes Street, Pittsburgh, Pa., marked for the attention of the "Supervising Engineer, Electrical-Mechanical Section."

Signature of Applicant

§ 25.4 Conditions governing investigations. (a) One complete unit, with assembly and detail drawings that show its construction and the materials of which it is made, should be forwarded to the Central Experiment Station at the time the application for approval is made.

(b) When the unit and drawings have been inspected by the Bureau's engineers, the applicant will be notified as to the amount of material that will be required for the tests.

(c) The applicant will be notified of the date on which tests will be started and will be given an opportunity to witness the tests.

(d) No one is to be present at the time the tests are made except the necessary Bureau of Mines engineers, their assistants, a representative of the applicant, and such other persons as may be mutually agreed upon by the applicant and the Bureau.

(e) Permissibility tests will not be made unless the unit has been completely developed and is in a form that can be marketed.

(f) The results of the tests shall be regarded as confidential by all present at the tests and shall not be made public in any way prior to the formal approval of the short-firing unit by the Bureau of Mines.

(g) No verbal report of approval or disapproval will be made to the applicant. After the Bureau's engineers have