Constructional Requirements for Electrical Equipment for Explosive Atmospheres

Article 54.  The surface joints of the enclosures of electrical equipment (hereinafter referred to as the electrical equipment) of dust-explosion protection 'ordinary enclosure' type, excluding those between the operating rods or rotating shafts and the enclosures (hereinafter the same in this Article) shall comply with the following requirements. However these requirements do not apply to the surface joints where gaskets are used.

(1) The surface roughness of joints shall be equal to or finer than 35-S specified in the Japanese Industrial Standard B0601 (Surface roughness).

(2) The widths of the joints shall not be less than 10 mm.

(3) They shall be very closely contacted.

2. Despite the main body of the text in the preceding para., the width of joints of the enclosures of small electrical equipment such as push-button switches, etc. may be not less than 6 mm where the surface roughness is not less fine than 18-S specified in the Japanese Industrial Standard B0601 (Surface roughness).

3. The gaskets specified in the proviso of the preceding para.1 shall comply with the following requirements:

(1) The materials shall endure the heat as the result of temperature-rise of the joints and shall not be easily damaged by wear, corrosion, etc.

(2) The configuration of gaskets shall be fit for that of the joints.

Article 55.  The surface joints between the operating shafts and the enclosures shall be so constructed that dusts outside find it difficult to enter the enclosures by fitting gaskets with gasket-glands or gasket-holders to the surface joints, providing rubber covers around the operating shafts, and so on.

Article 56.  The surface joints between the rotating shafts and the enclosures shall be so constructed that outside dusts find it difficult to enter the enclosures by fitting gaskets, adopting a labyrinth structure the gap and the joint width of which is not more than 0.5 mm and not less than 30 mm, respectively, and so on.

Article 57.  The requirements of para.3, Article 54 apply mutatis mutandis to the materials and configuration of gaskets specified in the two preceding Articles.

Article 58.  Screws used for maintaining dust-proofness shall be provided with fittings against unloosening.

2. Where the parts in the preceding para. Are screw-connected, the effective screw threads shall have at least the engagement of five.

Article 59.  Limits of temperature-rise of parts in the electrical equipment shall be taken lower by 10 percent less than the values specified in the general requirements for non-explosion-protected electrical equipment of the same kind. However, it may be reduced to 5 percent in the case where the electrical equipment is so constructed that the temperature-rise due to the accumulation of dusts is expected to be low.

2. Limits of temperature-rise of the enclosures which dusts may contact shall be 80 degrees for the electrical equipment such as motors, power transformers, etc. which may be overloaded, and shall be 110 degrees for the others.

Article 60.  When connecting the electrical equipment with external conductors, the terminal boxes of dust-explosion protection 'ordinary' type shall be used.

2. The provisions of para.2 of Article 14 apply mutatis mutandis where the electrical equipment is integral with two or more pieces of electrical equipment, those of para.1, Article 15 and Article 16 to the terminals in the preceding para., and Article 25 to types of leading conductors from the terminals to the body of the electrical equipment, respectively.

Article 61.  The provisions of Article 27 apply mutatis mutandis to the creepage distances and clearances in respect of bare live parts of the electrical equipment.

Article 62.  The surface joints (excluding those between the operating rods or rotating shafts and the enclosures, hereinafter the same in this Article) of the enclosures (hereinafter referred to as the enclosures in this Section)of electrical equipment (hereinafter referred to as the electrical equipment in this Section)of dust-explosion protection 'special enclosure' type, shall be fitted with gaskets which will not be detached or loosened. However these requirements do not apply in the case where it is difficult to use gaskets in the joints of the enclosures which are not necessary to be opened, where the surface roughness of joints is equal to or finer than 18-S specified in the Japanese Industrial Standard B0601 (Surface roughness) and where the width of joints are not less than 15 mm and the joints are closely contacted.

2. When using plane gaskets in applying the body of text in the preceding para., the widths of contact surfaces between the gaskets and the enclosures shall be at least the values given in the following table, corresponding to the length of joint surfaces.

Article 63.  The joint surfaces between the operating shafts and the enclosures shall be so constructed that the width of contact surfaces is not less than 10 mm and that gaskets with a packing gland are provided.

Article 64.  The joint surfaces between the rotating shafts and the enclosures shall be so constructed that the ingress of dusts from the outside is prevented by, for example, using gaskets of more than one layer or adopting a labyrinth structure, the gap and width of joints of which are not more than 0.5 mm and not less than 45 mm, respectively.

Article 65.  The provisions of para.3, Article 54 apply mutatis mutandis to the materials and configuration specified in the three preceding Articles.

Article 66.  Screws of parts which are necessary for maintaining dust-proofness and can be loosened from the outside shall be shrouded and provided with a fitting against loosening.

2. Where the parts in the preceding para. are screw-connected, the effective screw threads shall have at least the engagement of five and be fitted with a locking nut or gasket.

Article 67.  When connecting the electrical equipment with external conductors, a terminal box of dust-explosion protection 'special' type shall be used.

2. The provisions of para.2, Article 14 apply mutatis mutandis where the electrical equipment is integral with two or more pieces of electrical equipment, and the provisions of para.1, Article 15 and Article 16 to the terminal boxes in the preceding para., respectively.

Article 68.  Type of leading conductors from a terminal box of the dust-explosion-protection 'special' type shall be special dust-proof stud-type or special dust-proof packing-type.

Article 69.  The provisions of Article 59 apply mutatis mutandis to the temperature-rise of parts of the electrical equipment and Article 30 to the temperature-rise of insulated conductors, respectively.

Article 70.  The provisions of Article 27 apply mutatis mutandis to the creepage distances and clearances in respect of bare live parts of the electrical equipment.