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Constructional Requirements for Electrical Equipment for Explosive Atmospheres

(The Ministry of Health, Labour and Welfare Notification No. 16, 1969)

In Japanese

Chapter II. Types of gas-explosion protection

Section 1. Flameproof enclosures

Article 6. A flameproof enclosure (hereinafter referred to as the enclosure in this Section) on electrical equipment (hereinafter referred to as the electrical equipment in this Section) of the internal volumes (excluding those of iron cores, windings, contacts and parts which are requisite for operation, hereinafter the same) shown in the following table, shall withstand the internal pressures corresponding to the explosion classes of gases or vapours given in the table.

Internal volume (cm³)	Explosion class of gases & vapours	Internal pressure
Over 2 and not over 100	1 or 2	0.8 MPa
Over 2 and not over 100	3	1.5 times the maximum explosion pressure measured by the explosion test, or 0.8 MPa where the 1.5 times pressure is not more than 0.8 MPa
Over 100	1 or 2	1 MPa
Over 100	3	1.5 times the maximum explosion pressure measured by the explosion test, or 1 MPa where the 1.5 times pressure is not more than 1 MPa
The explosion test means a test conducted by exploding the gas or vapour in an enclosure having the same internal volume and configuration as the electrical equipment.

Article 7. The gap (excluding that between the enclosure and the rotating shaft, hereinafter the same in this Article) and the width of joints shall not be more than the maximum allowable gap and not be less than the minimum width of joints, respectively, corresponding to the internal volumes of the enclosure, as shown in the following table:

Internal volume V (cm³)	Gap and width of joint (mm)				Minimum allowable width of joint where there is a hole in the joint (L₁)
	Maximum allowable gap (W)			Minimum allowable width of joint (L)
	Explosion class 1	Explosion class 2	Explosion class 3	Minimum allowable width of joint (L)
V 2	0.3	0.2	0.1	5	5
2 V 100	0.2	0.1	50% of the max. gap which does not cause a flame propagation	10	6
100V 2000	0.25	0.15		15	8
2000 V	0.3	0.2		25	10
2000 V	0.4	0.25		40	15
Where the internal volume exceeds 2,000 cm³ and W exists between 0.3 and 0.4 for explosion class 1 or between 0.2 and 0.25 for explosion class 2, the values of L and L₁ shall be calculated by proportion from the numerals in the table.

2. The provision of the preceding para. is not applied where the joints need not be opened for operation or inspection, and where the gasket in conformity with the following items are mounted :

(1) The material shall be metallic or non-flammable.

(2) The width of contact planes between the gasket and the enclosure shall conform to the values of L in the preceding para. However, it may conform to the values of L₁ in the preceding para. where the gasket is press-fitted at all times.

(3) The gasket shall be mounted so as not to be pushed out from the place when an internal explosion occurs inside the enclosures.

Article 8. The gap and the width of the joints between a rotating shaft and the enclosure shall be not more than the maximum allowable gap and not less than the minimum width of joints, respectively, corresponding to the internal volume of the enclosures and the kind of bearings, as given in the following table:

Internal volume V (cm³)	Gap and width of joint (mm)
	kind of bearing
	Ball-and-roller bearings						Plain bearings
	Maximum allowable gap (the difference of diameter) (W)			Minimum allowable width of joint (L)			Maximum allowable gap (the difference of diameter) (W)			Minimum allowable width of joint (L)
	Explosion class			Explosion class			Explosion class			Explosion class
	1	2	3	1	2	3	1	2	3	1	2	3
V 2	0.45	0.3	0.15	5			0.3	0.2	0.1	5
2 V 100	0.3	0.2		10			0.2	0.1			15
100V 500	0.45	0.3		15			0.3			25
500 V	0.45	0.3		25			0.5			40
	0.6	0.4		40
50% of the maximum gap which does not cause a flame propagation in the explosion test Where the internal volume exceeds 500 cm³ and W of ball-and roller bearings exists between 0.45 and 0.6 for explosion class 1 or between 0.3 and 0.4 for explosion class 2, the values of L of ball-and roller bearings shall be calculated by proportion from the numerals in the table.

Article 9.  The surface joints in respect of the widths of the joints specified in the two preceding Articles shall comply with the following items:

(1) The material of one side of the surfaces shall be metallic.

(2) The surface roughness shall be equal to or finer than 25-S specified in the Japanese Industrial Standard B0601(Surface roughness), except where the surface roughness is equal to or finer than 35-S for the width of joints not less than 40 mm.

(3) Coating with paint or oil is not permitted, except where a thin oil film is applied for anti-corrosion or water-proofness.

Article 10.  Make-break contacts and conductors shall not be immersed in oil.

Article 11.  Where screws are used, the following requirements shall be met:

(1) Screws which are necessary for maintaining the flameproof properties of the joint and can be loosened from the outside shall be shrouded and provided with appropriate measures to prevent loosening.

(2) Screws for fastening the enclosure shall be strong enough to withstand sufficiently the pressure of an internal explosion.

(3) Screws shall not penetrate the walls of the enclosures, unless much difficulties arise in the construction of the enclosures if they are not allowed to penetrate the walls.

2. Where screws penetrate the walls of the enclosures and the holes for penetration are the clearance holes, the diametrical difference and the length of the penetration hole shall be not more than the maximum allowable gaps and not less than the minimum allowable widths of joint specified in Article 7, respectively.

Article 12.  Peep windows shall not be larger than 100 cm2 and shall be so constructed that the light transmitting plates can be replaced.

2. The light transmitting plates of peep windows shall comply with the following requirements:

(1) Light transmitting plates shall be made with the toughened glass specified in the Japanese Industrial Standard R 3206 (Toughened glass) or the laminated glass specified in the Japanese Industrial Standard R 3205 (Laminated glass), or with non-flammable materials equivalent in strength to the toughened or laminated glass.

(2) Light transmitting plates shall not be damaged when subjected to the impact of a 200 gr. steel ball falling from the height of 200 cm, under the condition of their mounting on peep windows.

Article 13.  The temperature-rise of external surfaces of the enclosures due to heat produced in live parts such as make-break contacts, windings, etc. shall not be more than the values of the limit of temperature-rise indicated in the following table, corresponding to the ignition group of gases and vapours:

Ignition group of gases and vapours	Values of limit of temperature-rise(degree)
G1 G2 G3 G4 G5	320 200 120 70 40

Article 14.  When the electrical equipment is connected with external conductors, the flameproof or increased safety terminal boxes shall be used.

2. Where the electrical equipment is integral with two or more pieces of electrical equipment and external conductors connecting each electrical equipment are safely protected, the terminal boxes mutually connecting electrical equipment may be omitted despite the preceding para.

Article 15.  The inside of flameproof terminal boxes shall comply with the following requirements:

(1) It has a sufficient space for connecting conductors.

(2) The terminals are arranged to make secure clamping possible.

2. The provisions of Article 27 apply mutatis mutandis to the creepage distances and clearances in respect of bare live parts inside the terminal boxes in the preceding para., and those of Article 28 to the mutual connections of live parts in the terminal boxes in the preceding para., respectively.

Article 16.  The flameproof terminal boxes shall have a grounding terminal at both the inside and the outside, except where threaded metallic conduits are utilized for a grounding conductor or where a grounding terminal is fitted inside the terminal boxes of movable electrical equipment.

Article 17.  The type of leading conductors from a flameproof terminal box to the main body of the electrical equipment shall be either flameproof-stud type or flameproof-packing type.

2. The provision of the preceding para. applies mutatis mutandis to types of leading conductors from an increased safety terminal box to the main body of the electrical equipment.

Section 2.  Pressurized enclosures

Article 18.  Protective gas purging supply which provides a protective gas for purging into the enclosures (hereinafter referred to as the enclosure) of electrical equipment of protection type 'pressurized enclosure' (hereinafter referred to as the electrical equipment) shall be able to maintain the internal pressure of both the electrical equipment and the relevant ducts at a value not less than 5 mm in water column when starting up and during service.

Article 19.  The electrical equipment of the preceding Article shall be fitted with the protective devices specified in the following items:

(1) The protective devices which do not permit the passage of current into the electrical equipment unless the passage of a protective gas of a volume not less than 5 times the internal volume of the enclosure has been completed

(2) The protective devices which are capable of sounding an alarm or cutting off the current automatically, in the cases where the protective gas pressure may not be maintained at or over 5 mm in water column.

Article 20.  The electrical equipment which is charged with a protective gas inside the enclosure shall be fitted with a protective device that is capable of sounding an alarm or cutting off the current automatically in the cases where the protective gas pressure drops, during service, lower than that necessary for preventing the ingress of gases or vapours for which the electrical equipment is designed, except where the electrical equipment which is made not to leak the protective gas is equipped with a pressure-indicating device.

Article 21.  The provisions of Article 13 apply mutatis mutandis to the temperature-rise of both the external surfaces of the enclosure and the protective gas exhausted from the enclosure.

Article 22.  Screws which are used for maintaining the properties of explosion-protection and can be loosened from the outside shall be shrouded.

Article 23.  For connecting the electrical equipment with external conductors, a pressurised, flameproof or increased safety terminal box shall be used.

2. The provision of para.2, Article 14 applies mutatis mutandis to the electrical equipment integral with two or more pieces of electrical equipment

Article 24.  Pressurized terminal boxes shall comply with the following requirements:

(1) They shall be totally enclosed, excluding the parts which are necessary for a passage of protective gas to the main body of the electrical equipment, and they shall not be provided with any exhaust holes.

(2)The boxes shall be so constructed that the surface joints and covers can be sealed.

2. The provisions of para.1, Article 15 and Article 16 apply mutatis mutandis to the terminal boxes in the preceding para., those of Article 27 to the creepage distances and clearances in respect of bare live parts inside the terminal boxes in the preceding para., and that of Article 28 to the mutual connections of live parts inside the terminal boxes in the preceding para., respectively.

Article 25.  Types of leading conductors from pressurized terminal boxes to the main body of the electrical equipment shall be stud-type, packing-type, sealing-type, bushing-type or clamping- type.

2. The provision of para.1, Article 17 applies mutatis mutandis to the types of leading conductors from flameproof terminal boxes to the main body of the electrical equipment, and that of the preceding para. to the types of leading conductors from increased safety terminal boxes to the main body of the electrical equipment, respectively.

Section 3.  Increased safety
Article 26.  Live parts (hereinafter referred to as the live parts in this Section) of increased safety electrical equipment (hereinafter referred to as the electrical equipment in this Section) shall be totally enclosed, excluding high-volt rotating machines, metallic resistors, batteries, etc. in which the live parts are sufficiently protected.

2. In the provision of the main text of the preceding para., at least one of the screws for fastening the covers of the enclosure in which bare live parts are housed, shall be shrouded .

Article 27.  The creepage distances and clearances shall not be less than the values given in the following table, corresponding to the values of rated voltage.

Rated voltage (volt)		Creepage distance (mm)				Clearance (mm)
D.C.	A.C.	Insulation Material 1	Insulation Material 2	Insulation Material 3	Insulation Material 4
V50 50 V220 220V440 440V600 600V750 750V1200 1200V1500	V50 50 V220 220V440 440V600 600V750 750V1200 1200V1500 1500V2000 2000V3300 3300V6600 6600V11000	3 6 8 10 14 20 28 36 50 90 125	4 6 10 12 18 24 32 42 60 110 150	6 10 12 16 22 30 40 50 72 130 180	6 12 16 20 28 36 50 70 90 160 240	3 6 8 8 10 14 20 28 36 60 100
1. Creepage distances and clearances applied to the wiring devices, circuit breakers for conductors, etc. on which the maximum allowable voltages are marked as a.c. rated voltages 250 or 600 volts, and which, however, the working voltages are not higher than 220 or 550 volts, respectively, shall be those corresponding to the rated voltage of 220 or 550 volts in this table.
2. Creepage distances and clearances applied to the disconnecting switches and a.c. circuit breakers on which the a.c. rated voltages are marked as 3,450, 3,600, 6,900 or 7,200 volts and which, however, working voltages are 3,000 or 6,000 volts, shall be those corresponding to the rated voltage of 3,300 or 6,600 volts, in this table, respectively.
3. Insulation materials 1, 2, 3 and 4 in the column of creepage distance shall be those given below; Insulation material 1 Porcelain, glass, natural mica, mica set by non-organic adhesives, or moulded insulating material with ribs which uses non-organic fillings and is stable against leakage current. Insulation material 2 Mica set by organic adhesives, moulded insulating material without ribs which uses non-organic fillings and is stable against leakage current,moulded insulating material with ribs which uses organic fillings and is stable against leakage current, or moulded phenol insulating material with ribs which uses non-organic fillings. Insulation material 3 Moulded insulating material without ribs which uses organic fillings and is stable against leakage current, moulded phenol insulating material without ribs which uses non-organic fillings, or laminated insulating material which is stable against leakage current. Insulation material 4 Varnish-coated and moulded phenol insulating material.

2. The creepage distances in respect of the wall of recessed bolts or screws shall be calculated as given in the following:

(1) In calculating the creepage distance where the gap between the rim of recessed bolts or screws and the wall of recesses is less than 3 mm, the path along the wall of recess from the top surface of recess to the top end of the bolts or screws shall be taken into account as a part of the creepage distance.

(2) In calculating the creepage distance where the gap between the rim of recessed bolts or screws and the walls of recess is not less than 3 mm, the path along the walls of recess from the top surface of recess to the bottom of recess shall be taken into account as a part of the creepage distance.

3. The creepage distances in respect of ribs shall be calculated as given in the following:

(1) Where the height or thickness of ribs is less than 3 mm, the creepage distance shall be the "line of sight" distance between conducting parts.

(2) Where the height or thickness of ribs is not less than 3 mm, the height shall be added in calculating the creepage distance.

(3) Where ribs are engrafted on an insulator, excluding those which are equivalent in insulation to those without engrafting, the contour of the engrafted parts shall be taken as parts of the creepage distance.

Article 28.  Mutual connections of live parts shall be conducted according to one of the following methods:

(1) Screwing with unloosening fittings

(2) Riveting or press-down connection

(3) Soldering reinforced with sleeves, binding wires, etc.

(4) Brazing by hard solder

(5) Welding

Article 29.  The surface area of peep windows shall be as small as necessary, and the light transmitting plates shall be replaceable.

2. The light transmitting plates shall not be damaged when subjected to the impact of a 50 gr. steel ball falling from the height of 100 cm, under the condition that they are fixed to the peep windows.

Article 30.  Limits of temperature-rise of insulated windings in the electrical equipment shall be taken lower by 10 degrees less than the values specified in the general requirements for the same kind of non-explosion-protected electrical equipment.

Article 31.  The provisions of Article 13 apply mutatis mutandis to the temperature-rises of parts where gases and vapours may be accessible.

Article 32.  For connecting the electrical equipment to external conductors, an increased safety or flameproof terminal box shall be used.

2. The provision of para.2, Article 14 applies mutatis mutandis to the electrical equipment integral with two or more pieces of electrical equipment.

Article 33.  The surface joints of increased safety terminal boxes shall comply with one of the following requirements:

(1) The width of joints shall not be less than 10 mm, the roughness shall be equal to or finer than 35-S specified in the Japanese Industrial Standard B0601(Surface roughness), and the joints shall be so constructed that they are sufficiently pressed on at all times, excluding small terminal boxes where the width of joints is not less than 6 mm and the surface roughness is equal to or finer than 18-S.

(2) The gaskets shall be made of metal, asbestos, glass fiber, synthetic rubber or other materials of heat-resistance and durability, and shall be so constructed that they are sufficiently pressed at all times.

2. The provisions of para.1 of Article 15 and Article 16 apply mutatis mutandis to the terminal boxes in the preceding para., Article 27 to the creepage distances and clearances in respect of bare live parts inside the terminal box in the preceding para., and Article 28 to the mutual connections of live parts in the terminal boxes in the preceding para., respectively.

Article 34.  The provision of para.1 of Article 17 applies mutatis mutandis to the types of leading conductors from a flameproof terminal box to the main body of the electrical equipment and that of para.1 of Article 25 to the types of leading conductors from an increased safety terminal box to the main body of the electrical equipment, respectively.

Section 4.  Oil-immersion
Article 35.  The enclosures of type of protection 'oil-immersion' shall be totally enclosed.

Article 36.  Parts of the electrical equipment in the preceding Article, which are not immersed in oil, shall be of protection 'increased safety' type.

Article 37.  The oil tanks shall be equipped with an oil gauge or other appropriate devices which can easily check the height of the oil.

Article 38.  Oil gauges shall be in compliance with the following requirements:

(1) It is strongly constructed, and the light transmitting plates or tubes shall be replaceable

(2) The light transmitting plates or tubes and the gaskets shall not be deteriorated due to the effect of hot oil.

(3) Fluctuations in the oil surface due to the oil temperature changes shall be discernible from the outside.

Article 39.  The oil gauges, etc. set forth in Article 37 shall be so constructed that in the instance where the insulating oil leaks as a result of damages, etc., the oil surface is maintained at a safe level over which high temperature parts that may become an ignition source, sparks or arcs will not appear.

Article 40.  Screws which are used for maintaining the properties of explosion-protection and can be loosened from the outside shall be shrouded.

2. Screws used for discharging the oil shall be provided with unloosening devices, in addition to the requirements of the preceding para.

Article 41.  Oil switches, excluding those which are so constructed that an accumulation of decomposed gases due to arcs is small, whose rated making-breaking capacity is over 1 kVA or breaking capacity is over 25 kVA, shall have holes for gas exhaust.

Article 42.  The temperature-rise of oil surfaces shall not be more than the values of limit of temperature-rise shown in the following table, corresponding to the ignition group of gases and vapours for which the electrical equipment is designed, respectively.

Ignition group of gas or vapour	Limit of temperature-rise (degree)
G1 G2 G3 G4 G5	60 60 60 60 40

Section 5.  Intrinsic safety
Article 43.  Electrical equipment of protection 'intrinsic safety' type (hereinafter referred to as the electrical equipment in this Section) shall have the circuits (hereinafter referred to as intrinsically safe circuits) in which any sparks, arcs or heat that will occur in normal operation or under short-circuits, grounding faults or wire-breaking conditions do not become an ignition source of gases or vapours.

Article 44.  Parts constituting intrinsically safe circuits shall be totally enclosed, except where a total enclosure may impair the normal functioning of the electrical equipment and the live parts of the intrinsically safe circuits are sufficiently protected.

Article 45.  Wiring of intrinsically safe circuits shall use a single conductor of not less than 0.3 mm in diameter or a conductor of the same sectional area.

2. Where the conductor set forth in the preceding para. is a stranded wire, the diameter of the element shall not be less than 0.3 mm in diameter.

Article 46.  In electrical equipment (hereinafter referred to as the associated electrical equipment in this Section) consisting of intrinsically safe and non-intrinsically safe circuits (which are those other than intrinsically safe circuits, hereinafter the same), the conductors of both circuits shall not be bundled together or included in a multi-core cable, except where each circuit conductor is mutually shielded with certainty.

Article 47.  Insulated conductors used in the associated electrical equipment shall comply with the following requirements:

(1) The insulated conductors of intrinsically safe circuits shall have a dielectric strength of 800 volts a.c. and those of non-intrinsically safe circuits 2,000 volts a.c., respectively.

(2) Colours of insulated conductors of intrinsically safe circuits and non-intrinsically safe circuits shall not be the same.

Article 48.  The dielectric strength of intrinsically safe circuits to the ground shall not be lower than 500 volts a.c.

Article 49.  The requirements of Article 27 apply mutatis mutandis to the creepage distances and clearances for preventing an ignition of gases or vapours due to sparks, arcs or heat which are caused by the contacts of intrinsically safe circuits and non-intrinsically safe circuits. In this case,
the rated voltage shall be taken as the sum of each rated voltage of the two circuits.

2. Despite the preceding para., the creepage distance and clearance of printed circuits which are coated with resin, etc. may be reduced to one third of the values shown in the table of Article 27 applied mutatis mutandis in the preceding para.

Article 50.  Where the terminals of intrinsically safe circuits and non-intrinsically safe circuits are arranged on the same connection part, appropriate measures shall be taken for preventing accidental contacts of both circuits, such as by a separation not less than 50 mm or by installing isolating walls of sufficient strength and insulation.

Article 51.  Among intrinsically safe circuit elements, those necessary for operation of the circuits shall comply with the following requirements:

(1) Semi-conductors shall have a sufficient capacity.

(2) Condensers shall be of sealed-type, and their rated voltages shall not be less than 3 times the voltages applied to them.

(3) Two equivalent elements, excluding those given below, shall be used in parallel:

  a. The isolating transformers which connects an intrinsically safe circuit and a non-intrinsically safe circuit and has the following construction and ability;

    (a) When the external terminals are exposed, the distance between the terminals of different windings shall not be less than 50 mm or the terminals shall be protected with insulating materials against accidental contacts.

    (b) The isolating plate shall be made of copper of not less than 0.1 mm in thickness and be constructed to isolate the windings with certainty.

    (c) The primary windings shall withstand a voltage of 2,500 volts a.c. applied for one minute between the windings and the isolating plate.

    (d) The secondary windings shall withstand a voltage of 1,500 volts a.c. applied for one minute between the windings and the isolating plate.

  b. Wire-wound resistors which are used for limiting circuit currents and protected against wire-loosening when the wire is broken.

  c. Wire-wound resistors coated with or potted in resin, etc., with a diameter of not less than 0.2 mm and used at a power not more than half the rated power.

  d. Damping wires or those having the same function, assembled together with the relevant windings and mounted not to be detached from the outside.

Article 52.  The associated electrical equipment, the non-intrinsically safe circuits of which are not explosion-protected, shall clearly show the following in addition to those markings stipulated in para.1 of Article 4:

(1) Not to be installed in hazardous locations.

(2) No amendments, etc. allowed to parts of the electrical equipment, wiring, etc.

(3) For the terminals of intrinsically safe circuits in the associated electrical equipment, their identification.

Section 6.  Special
Article 53.  Electrical equipment of protection 'special' type shall be confirmed the properties of xplosion-protection against gases and vapours by tests, etc.

Chapter II