1 Scope
This standard is to be read in conjunction with GB 12476, the requirements of which apply to electrical apparatus protected by encapsulation and surface temperature limitation unless specifically excluded.
This part is applicable to electrical apparatus protected by encapsulation type of protection “mD" and surface temperature limitation for use in areas where combustible dust may be present in quantities which could lead to a fire or explosion hazard. It specifies requirements for design, construction and testing of electrical apparatus, parts of electrical apparatus and Ex components where the rated voltage does not exceed 10 kV.
Note 1: The actual working voltage may exceed the value given above by up to 10 %.
Note 2: GB 12476.2 Electrical apparatus for use in the presence of combustible dust – Part 14: Selection and installation gives guidance on the selection and installation of the apparatus. Apparatus within the scope of this standard may also be subjected to additional requirements in other standards – for example, GB 3836.1 Explosive atmospheres—Part 1:Equipment—General requirements.
The application of electrical apparatus in atmospheres which may contain explosive gas as well as combustible dust, whether simultaneously or separately, requires additional protective measures.
This standard does not apply to dusts of explosives which do not require atmospheric oxygen for combustion, or to pyrophoric substances.
This standard is not applicable to electrical apparatus intended for use in underground parts of mines as well as those parts of surface installations of such mines endangered by firedamp and/or combustible dust.
This standard does not take account of any risk due to an emission of flammable or toxic gas from the dust.
This standard does not include other types of protection and is only applicable to protection by encapsulation.
2 Normative references
The following normative documents contain provisions which, through reference in this part, constitute provisions of this part of GB 12476. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this part are encouraged to investigate the possibility of applying the most recent editions of the normative documents listed below. For undated references, the latest edition of the normative document referred to applies.
GB/T 1034-2008 Plastics - Determination of water absorption (ISO 62:2008, IDT)
GB/T 1408.1-2006 Electrical strength of insulating materials - Test methods - Part 1: Tests at power frequencies (IEC 60243-1:1998, IDT)
GB 3836.3-2010 Explosive atmospheres—Part 3:Equipment protection by increased safety e (IEC 60079-7:2006, IDT)
GB 3836.4-2010 Explosive atmospheres—Part 4:Equipment protection by intrinsic safety i (IEC 60079-11:2006, IDT)
GB/T 8897.1-2003 Primary batteries - Part 1:General (IEC 60086-1:2000, IDT)
GB 9364 (all parts) Miniature fuse (IEC 60127 series, IDT)
GB 9816-2008 Thermal-links - Requirements and application guide (IEC 60691:2002+A1:2006, IDT)
GB 12476.4-2010 Electrical apparatus for use in the presence of combustible dust - Part 4:Protection by intrinsic safety “iD” (IEC 61241-11:2005, IDT)
GB/T 16855.1-2005 Safety of machinery – Safety-related parts of control systems – Part 1:General principles for design (ISO 13849-1:1999, MOD)
GB/T 16935.1-2008 Insulation coordination for equipment within low-voltage systems - Part 1: Principles requirements and tests (IEC 60664-1:2007, IDT)
GB 19212.7-2006 Safety of power transformers power supply units and similar - Part 7: Particular requirements for safety isolating transformers for general use (IEC 61558-2-6:1997, MOD)
IEC 60285 Alkaline secondary cells and batteries - Sealed nickel-cadmium cylindrical rechargeable single cells
IEC 60622 Secondary cells and batteries containing alkaline or other non-acid electrolytes – Sealed nickel-cadmium prismatic rechargeable single cells
IEC 60664-1:1992 Insulation co-ordination for equipment within low-voltage systems – Part 1: Principles, requirements and tests
Amendment 1 (2000)
Amendment 2 (2002)
IEC 61150 Alkaline secondary cells and batteries – Sealed nickel cadmium rechargeable monobloc batteries in button cell design
IEC 61241-0:2004 Electrical apparatus for use in the presence of combustible dust – Part 0: General requirements )
IEC 61241-1:2004 Electrical apparatus for use in the presence of combustible dust – Part 1: Protection by enclosures “tD”
IEC 61436 Secondary cells and batteries containing alkaline or other non-acid electrolytes – Sealed nickel-metal hydride rechargeable single cells
IEC 61960-1 Secondary lithium cells and batteries for portable applications – Part 1: Secondary lithium cells
IEC 62326-4-1 Printed boards – Part 4: Rigid multilayer printed boards with interlayer connections – Sectional specification – Section 1: Capability detail specification – Performance levels A, B and C
ANSI/UL 248-1 Standard for low-voltage fuses – Part 1: General requirements
ANSI/UL 746B Polymeric Materials – Long-term Property Evaluations
3 Terms and definitions
For the purposes of this document, the following terms and definitions, specific to protection by encapsulation "mD“, apply. They supplement the definitions given in the general requirements.
3.1
“mD” encapsulation “mD”
type of protection whereby parts that are capable of igniting an explosive atmosphere by either sparking or heating are enclosed in a compound in such a way as to avoid ignition of a dust layer or cloud under operating or installation conditions
3.2
compounds
any thermosetting, thermoplastic, epoxy resin or elastomeric materials with or without fillers and/or additives, in their solid state
3.3
temperature range of the compound
the range of temperatures within which the properties of the compound, in either operation or storage, permit compliance with the requirements of this standard
3.4
continuous operating temperature (COT) of the compound
the temperature within which, according to the details given by the manufacturer, the properties of the compound, during operation, satisfy the requirements of this standard during the foreseen lifetime of the apparatus
3.5
encapsulation
the process of applying the compound to enclose any electrical device(s) by suitable means
3.6
free surface
compound surface exposed to the explosive atmospheres
3.7
normal operation
the operation of apparatus conforming electrically and mechanically with its design specification and used within the limits specified by the manufacturer
Note 1: The limits specified by the manufacturer may include persistent operational conditions, for example, operation of a motor on a duty cycle.
Note 2: Variation of the supply specifications within stated limits and any other operational tolerance is part of normal operation.
3.8
void
unintentional space created as a consequence of the encapsulation process
3.9
free space
intentionally created space surrounding components or space inside components
3.10
switching contact
mechanical contact which is intended for making and breaking of an electrical circuit
Foreword I
Introduction III
1 Scope
2 Normative references
3 Terms and definitions
4 General
5 Requirements for compounds
6 Temperatures
7 Constructional requirements
8 Type tests
9 Routine verifications and tests
10 Marking
Annex A (informative) Basic requirements for compounds for encapsulation “mD” apparatus
Annex B (normative) Allocation of test samples
Annex C (normative) Test procedure during thermal cycling test
Figure 1 Distances between free surface of compound and components or conductors
Figure 2 Distances between the wall or the free surface of the compound and the components or conductors
Figure 3 Distances between the wall or the free surface of the compound and the components or conductors
Figure 4 Minimum distances for multi-layer printed wiring boards
Figure A.1 Basic requirements for compounds for encapsulation “mD” apparatus
Annex B (normative) Allocation of test samples
Figure C.1 Test procedure during thermal cycling test
Table 1 Distances through the compound
Table 2 Thickness of compound between the free surface of the compound and components or conductors
Table 3 Thickness of the compound between the wall or the free surface of the compound and the components or conductors
Table 4 Thickness of the compound between the wall or the free surface of the compound and the components or conductors
Table 5 Minimum distances for multi-layer printed wiring boards
Table 6 Permissible primary cells
Table 7 Permissible secondary cells
Table 8 Test pressure
Table B.1 Allocation of test samples
