Constructional Requirements for Electrical Equipment for Explosive Atmospheres

Article 1.  In this Notification, the terms and definitions given in the following apply:

(1) Enclosure    an enclosure which is requisite for maintaining explosion-protection properties of electrical equipment, such as external casings, external coverings, protective covers, etc.

(2) Surface joint    place where corresponding surfaces of parts of an enclosure of electrical equipment come together, with a gap having a passage from the inside of the enclosure to the outside

(3) Type of gas-explosion protection "Flameproof enclosure"    type of protection applied to an enclosure which can withstand internal explosion pressure and prevent the ignition of flammable gases (hereinafter referred to as gases) or ignitable vapours (hereinafter referred to as vapours) surrounding the enclosure by the flame of explosion, when gases or vapours enter the enclosure and cause an internal explosion.

(4) Type of gas-explosion protection "Pressurized enclosure"    type of protection applied to an enclosure, the ingress of external gases or vapours into which is guarded by supplying or enclosing a protective gas, such as air, nitrogen, carbon dioxide, etc.

(5)Type of gas-explosion protection "Increased safety"     type of protection applied to parts(excluding non-current-passing parts) of electrical equipment, which, during normal service or under normal current-carrying conditions, do not cause arcs or sparks or high temperatures capable of becoming an ignition source and to which an increased degree of safety is provided in terms of insulation, temperature-rise, mechanical damage from the outside, etc.

(6) Type of gas-explosion protection "Oil-immersion"     type of protection in which parts of electrical equipment, which can cause sparks or arcs or high temperatures capable of becoming an ignition source, are immersed in an insulating oil, and thus preventing the ignition of gases or vapours

(7) Type of gas-explosion protection "Intrinsic safety"     type of protection in which any sparks, arcs or heat occurring in parts of electrical equipment have been confirmed by tests, etc. that they are incapable of causing the ignition of gases or vapours

(8) Type of gas-explosion protection "Special"     type of protection applied to electrical equipment, other than those defined in the above (3) through (7), and the explosion-protection properties of electrical equipment against gases or vapours are confirmed by tests, etc.

(9) Type of dust-explosion protection "Ordinary enclosure"     type of protection in which an enclosure is so constructed that outside dusts find it difficult to enter the enclosure by providing surface joints with a gasket, or by making the width of surface joints longer and so forth, and in which temperature-rise of the enclosure is limited so that the ignition of flammable dusts (except for explosive dusts) outside the enclosure does not occur

(10) Type of dust-explosion protection "Special enclosure"     type of protection in which an enclosure is so constructed that dusts outside the enclosure are prevented from entering the enclosure by providing surface joints with a gasket, etc. and in which the temperature-rise of the enclosure is limited so that the ignition of explosive dusts outside the enclosure does not occur by limiting temperature-rise of the enclosure

(11) Gap    maximum distance between the corresponding parts or surfaces of a joint, or maximum difference between the diameters of the bore and the cylindrical component, when the inside of electrical equipment is below the atmospheric pressure

(12) Width of joint    shortest path through a joint corresponding to the gap when the gap is maintained at or less than the allowable value given in para.1, Article 7 and Article 8, respectively

(13) Explosion class    degree of ignitability of gas or vapour, classified according to the minimum distance between the corresponding surfaces of a joint of the test enclosure when the explosion test is conducted and a flame propagation occurs to the exterior (hereinafter referred to as " flame propagation limit" )

(14) Ignition group    degree of flammability of gas or vapour according to the value of the ignition point

(15) Shrouding    structure applied to parts surrounding the heads of screws fastening an enclosure of electrical equipment where the screws are incapable of being loosened without special tools

(16) Creepage distance    shortest distance along the surfaces of insulating materials between a bare live part and other parts which shall be insulated from the bare live part

(17) Clearance    shortest distance through air between a bare live part and other parts which shall be insulated from the bare live part

Article 2.  Electrical equipment under the provision of para.1, Article 280 of the Ordinance on Industrial Safety and Health (the Ministry of Labour Ordinance No.32, 1972) (hereinafter referred to as "the Ordinance") shall be of protection 'flameproof enclosure' type, 'pressurized enclosure', 'increased safety', 'oil immersion', 'intrinsic safety' or 'special'.

2. Electrical equipment under the provision of para.1, Article 281 of the Ordinance shall be of dust-explosion protection type 'ordinary enclosure' or 'special enclosure'.

3. Electrical equipment under the provision of para.1, Article 282 of the Ordinance shall be of dust-explosion protection 'special ' type.

Article 3.  Electrical equipment shall be so constructed that it is easily inspected and repaired; and the materials used shall be electrically, mechanically, thermally and chemically durable.

Article 4.  Electrical equipment shall attach to easily visible part with label which indicates the following items:

(1) Type of (gas- or dust-explosion) protection: Electrical equipment integral with two or more types of protection may indicate only a type of protection applied to the main body of electrical equipment, except when necessary for proper handling or securing safety.

(2) Explosion class (only for 'flameproof enclosures' ) and ignition group: Where gases and vapours are specified, the indication of explosion class and ignition group may be omitted by instead indicating their names.

(3) Ratings of circuits in electrical equipment of protection type 'intrinsic safety' or 'special ' and the essential points of conditions of use:

2. Type of protection, explosion class and ignition group shall be indicated by the symbols shown in the following tables, respectively:

(1) Kind of type of protection

(2) Explosion class

(3) Ignition group

3. Despite the provisions of the two preceding paragraphs for electrical equipment which is considered to be in conformity with the provisions of Chapter 2 (excluding Section 6) through Chapter 4, based on the following Article, the method of the indication according to the two preceding paragraphs may be that approved by the Director-General of the Labour Standards Bureau, the Ministry of Health, Labour and Welfare.

Article 5.  Among electrical equipment not in conformity with the provisions of Chapter 2(excluding Section 6) through Chapter 4 (hereinafter referred to as the provisions in this Article), that in which special materials are used or special configurations are adopted, or which is used in special locations, or which is manufactured on the basis of the international standards relevant to the provisions and confirmed by tests, etc. to be equivalent in explosion-protection properties to that in conformity with the provisions, is deemed to be in conformity with the provisions.