mechanical fastening in addition to the lock. (2) On locomotives and other mobile storage-battery-operated equipment, receptacles used for charging purposes only shall be provided with a cover or dummy plug that is to be locked in place when the battery is not being charged to prevent access to live terminals while the equipment is in operation. (3) A plug that is used for connecting the portable cable of one permissible machine to a circuit on another permissible machine shall be interlocked so that the plug can neither be inserted nor withdrawn while the plug or receptacle contacts are alive. If the interlock does not prevent making the receptacle contacts alive when a plug is out, the contacts shall be protected by a cap or cover to be locked in place when the plug is out, or the contacts shall be arranged to prevent ready access to them. A chain or its equivalent shall be provided to prevent loss of the cover. The circuit served by the plug shall be protected by fuses or other automatic circuit-interrupting devices as specified in § 18.2 (b) (4). (4) When the portable cable for a machine is arranged to be connected and disconnected from it by means of a plug, the plug shall be interlocked or constructed so that it can be inserted and withdrawn without creating the hazard of igniting gas or dust. In addition, the plug shall be kept locked in its receptacle to prevent removal by unauthorized persons. The contacts in the plug shall be adequately shielded or recessed in it to prevent accidental grounds or short circuits while the plug is out of its receptacle. (5) When single-pole plugs are used for the individual conductors of a cable or circuit, the design shall prevent energizing the circuit unless all the plugs of the circuits are in place. (6) Every plug shall have a suitable holding device or clamp to prevent any strains coming on the plug while it is in its receptacle, unless the interlock is of adequate strength to hold the plug securely in place. In either case, the design of the plug shall include an insulated clamp for holding the cable to prevent strains on the connections in the plug. § 18.5 Detailed inspection. (a) In the investigation of any equipment, explo sion-proof casings shall be given a careful inspection by the Bureau's engineers. This inspection shall include the following items. (1) A detailed check of parts against drawings as to materials, dimensions, and position, making notations for necessary correction of discrepancies between the drawings and the parts checked. (2) Measurement of joints, bearings, and other possible flame paths. (3) Examination for unnecessary through holes. (4) Examination for adequacy of lead-entrance design and construction. (5) Examination for adequacy of electrical clearances or insulation between live parts of opposite polarity and between live parts and ground. (6) Examination for adequacy and security of fastenings. (b) For further information regarding the details of this inspection, reference should be made to Information Circular 7185, Inspection and Testing of MineType Electrical Equipment for Permissibility. § 18.6 Character of tests-(a) Explosion tests. (1) To test enclosures for their ability to retain flame, they will be filled and surrounded with explosive mixtures containing varying percentages of Pittsburgh natural gas' and air. The mixture within the enclosures will be ignited by a spark plug or other suitable means, and a record of explosion pressures developed will be taken. The point of ignition will be varied to determined the condition that gives the greatest pressure. For some of the tests, bituminous-coal dust will be introduced into enclosures, and the effects will be noted. Motor armatures and rotors will be stationary in some tests and revolving in others. (2) Not less than 10 tests will be made of each design of explosion-proof enclosure. If, on account of the size of enclosure or questionable construction fea * Investigation has shown that, for practical purposes, Pittsburgh natural gas (containing a high percentage of methane) is a satisfactory substitute for pure methane in these tests. If the internal air space of a squirrelcage induction motor is not changed by more than 20 percent of that of a previously tested motor, it may be accepted without further inspection or explosion test, provided the motor of greater (or less) internal volume has the same frame diameter and the same length and clearance at the flame path of all Joints and bearings as those of the previously tested motor. tures, it is the judgment of the Bureau's engineers that the explosion-proof qualities cannot be completely demonstrated in 10 tests, more than that number will be made. (3) The explosion tests of an enclosure shall not result in: (1) Discharge of flame from any joint, bearing, or opening, (ii) ignition of surrounding explosive mixtures, (iii) development of dangerous afterburning, or (iv) rupture or permanent distortion of the enclosure. An enclosure will be rejected if failing to meet any one of the foregoing conditions and also if abnormal pressures are developed or potentially hazardous conditions are exhibited by the tests. (b) Adequacy tests. In addition to explosion tests, certain other tests may be made at the option of the Bureau's engineers, such as tests to determine the adequacy of an accessory for the service intended: (1) Where the durability of battery cells, headlights, or other parts is in doubt, such mechanical tests as are deemed necessary may be made to determine points requiring strengthening. (2) If there is any question on the efficacy of ventilation of battery boxes, tests may be made to check the ventilation. (3) Switches and devices serving as switches shall be capable of interrupting any overload currents that the automatic circuit protective devices will permit to flow. They also shall be capable of opening these overloads five times at 2-minute intervals without grounding or short-circuiting, and tests may be made to determine their ability to meet these requirements. (4) Fuses or other automatic circuitinterrupting devices may be tested to determine whether they provide the necessary protection without damaging the explosion-proof qualities of their enclosures. (c) Portable cable run-over test. (1) The run-over test in subparagraph (2) of this paragraph 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 term "afterburning" as used in this Part 18 is applied to combustion, immediately after an internal explosion, of a gaseous mixture that was not in the enclosure at the time of that explosion but was drawn in as the result of the cooling of the products of the original explosion or otherwise. (2) 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. (d) Portable cable flame-resistance test. The following test has been established for determining the flame-resistant properties of portable cables: (1) 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: CONDUCTOR SIZE, A. W. G. 14 12 10 8 6 4 3 2 1 0 00/000/0000 CURRENT, AMPERES 18 23 31 41 54 72 83 96 110 127 145 166 193 (2) This heating shall be continued until the temperature of the sheath between 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. (3) 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. (4) 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. [Schedule 2E, 10 F. R. 2238, as amended at 12 F. R. 7286] § 18.7 Inspection and test of parts supplied by other manufacturers. All the accessory parts for an approved ma chine 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 25, 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 The may be advertised and labeled as 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 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. [12 F. R. 7286] 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. § 18.8 Final inspection. (a) In addition to the detailed inspections and the tests, the Bureau reserves the right to inspect the machine as a whole at the close of the investigation to ascertain whether the assembly of motors, controllers, rheostats, and other parts in relation to each other has any unsafe features, special note being made of the position and guarding of wiring between these parts. The drawings and specifications also will be checked to see that they have been corrected to show all changes made in parts during the course of the investigation. (b) Manufacturers shall notify the Supervising Engineer, Electrical-Mechanical Section, at the Central Experiment Station, when the first of a given design of machine built for approval will be completed in order that a Bureau engineer may have an opportunity to examine it, when such examination is considered necessary. Examinations are preferably made at the factory, where cranes and other facilities make it possible to inspect a machine more thoroughly and quickly than elsewhere. Final inspections are made before approvals are granted. § 18.9 Inspection and test reports. Written reports, giving the results of inspections and tests, will be made to the manufacturer to keep him informed of the progress of the investigation of his equipment. These reports also will indicate whether or not any changes are required. They are not to be construed as giving approval to the equipment under consideration, or to any of its parts. § 18.10 Approvals—(a) Approval letter. (1) After all tests, as well as detailed and final inspections, have been satisfactorily completed and suitable drawings and specifications have been placed on file, the manufacturer of the completed equipment will be given official notification by letter from the Director of the Bureau of Mines at Washington 25, D. C., stating that his equipment has been judged to satisfy the conditions of this part and that it is therefore approved as permissible for use in gassy and dusty mines. The letter will assign an approval number for reference and identification of the equipment approved. No informal, temporary, or verbal approvals will be granted. (2) An official drawing list numbered to correspond to the approval number assigned will accompany each approval letter. This list will include the drawings and specifications covering the details of construction upon which the approval is based. (3) The manufacturer shall not advertise his equipment as permissible or approved until he has received the formal notification of approval from Washington. (b) Approval plate. (1) With the approval letter the manufacturer will receive a photograph of a design of approval plate. This plate shall bear the seal of the Bureau of Mines, United States Department of the Interior, a space for the approval number, the name of the class of equipment to which the equipment belongs, and the name of the manufacturer. When necessary, an appropriate statement giving the precautions to be observed in maintaining the equipment in an approved condition shall be added. (2) The manufacturer himself shall have this design reproduced either as a separate plate or by stamping or molding it in some suitable place on each permissible machine. The size and location of the approval plate shall be satisfactory to the Bureau, and a sample of the plate adopted shall be sent to the Supervising Engineer, Electrical-Mechanical Section, at the Central Experiment Station. The method of attaching the plate shall not impair the explosion-proof features of any enclosure. (c) Purpose and significance of approval plate. (1) The approval plate is a label which identifies the equipment so that anyone can tell at a glance whether or not that equipment is of permissible type. This plate is the manufacturer's guarantee that his equipment complies with the requirements of the Bureau of Mines and that it has been judged to be suitable for use in gassy and dusty mines. Without a plate, an approved machine loses its permissible status. (2) The use of the approval plate on his equipment obligates the manufacturer to maintain the quality of his product and to see that each permissible machine is constructed according to the drawings and specifications accepted and recorded by the Bureau. Equipment having changes in design which do not have official authorization from the Bureau is not permissible and therefore must not bear an approval plate. (d) Withdrawal of approval. The Bureau reserves the right to rescind for cause, at any time, any approval granted under the regulations in this part. § 18.11 Changes in design after approval. Every approval is granted with the understanding that all equipment built under that approval will be in exact accordance with drawings and specifications that have been examined and recorded by the Bureau in the approval. Therefore, when a manufacturer desires to make any change in the design of his approved equipment, he shall first of all obtain the Bureau's authorization of the change. The procedure is as follows: (a) The manufacturer shall write a letter to the Director, Bureau of Mines, Washington 25, D. C., applying for an extension of his original approval and describing the change or changes proposed. This letter should be accompanied by a certified check or bank draft payable to the Treasurer of the United States to cover all the necessary fees. If the applicant is uncertain as to the amount he should submit, the information will be given him upon inquiry addressed to the Supervising Engineer, Electrical-Mechanical Section, at the Central Experiment Station, 4800 Forbes Street, Pittsburgh 13, Pa. A copy of the application, together with revised drawings and specifications showing the changed design in detail, should be sent to the Supervising Engineer, ElectricalMechanical Section, at the Central Experiment Station. (b) The Bureau will consider the application and examine the drawings and specifications to determine whether they are sufficiently detailed for the Bureau's records and whether it will be necessary to have the modified part submitted for tests. (In general, changes increasing the air space more than 10 percent, modification of joints and bearings, or use of a different material for explosion-proof enclosures will make explosion tests of the modified enclosure necessary. Adequacy tests also may be necessary if changes such as reduction in electrical clearance and insulation are proposed.) If tests are judged to be necessary, the applicant will be informed of the parts that will be required. (c) When the modification has been found to comply with the requirements of the regulations in this part, both as to construction and drawings, formal authorization, known as an extension of Page 91 Lists of § 19.1 Purpose. (a) The purpose of investigations made under this part is to promote the development of electric cap lamps that may be used in mines, especially in mines that may contain dangerous concentrations of methane. such lamps will be published from time to time in order that State mine-inspection departments, compensation bureaus, mine operators, miners, and others interested in safe equipment for mines may have information in regard to available permissible electric cap lamps. This part supersedes Schedule 6C issued under date of December 21, 1935, and goes into effect August 26, 1939. (b) Any electric cap lamp that meets the requirements set forth in this part will be termed "permissible" by the Bureau and, if actively marketed, will be listed as such in publications relating to permissible electric cap lamps. § 19.2 Fees charged—(a) Item 1. The fee for a complete investigation of an (2) All applications for such tests must be made by the manufacturer of the cap lamp. (c) Item 3. Under the present provisions of this part, extensions of approvals that do not require tests will be made without charge. (d) Item 4. Tests to assist manufacturers in the development of electric cap lamps may be made upon request to the Director of the Bureau of Mines and will be charged for in amounts proportionate to the work involved. The making of this class of tests shall, however, be optional with the Bureau. § 19.3 Instructions for making applications. (a) Before the Bureau of Mines will undertake the active investigation of any equipment, manufacturers shall have filed an application in the form of a letter requesting that the necessary inspections and tests leading to approval be made and shall have made the necessary deposit to cover the fee for the tests. (b) A sample request for an investigation of an electric cap lamp follows: THE DIRECTOR OF THE BUREAU OF MINES, DEPARTMENT OF THE INTERIOR, Washington 25, D. C. cap lamp. ---- Subject: Tests of the DEAR SIR: We hereby make application for an investigation leading to the approval of the electric cap lamp under the provisions of Schedule 6D. Attached is a check for two hundred dollars ($200), made payable to the Treasurer of the United States, to cover the fee for the investigation. A copy of this application, one set of drawings, one complete lamp, and a full set of instructions for operating the lamp are being sent to the Central Experiment Station, |