GB/T 3836.31-2021 PDF English
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GB/T 3836.31-2021: Explosive atmospheres - Part 31: Equipment dust ignition protection by enclosure 't'
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NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 29.260.20
CCS K 35
Replacing GB 12476.5-2013
Explosive atmospheres - Part 31.Equipment dust ignition
protection by enclosure “t”
(IEC 60079-31.2013, NEQ)
Issued on. OCTOBER 11, 2021
Implemented on. MAY 01, 2022
Issued by. State Administration for Market Regulation;
Standardization Administration of the PRC.
Table of Contents
Foreword... 3
Introduction... 6
1 Scope... 9
2 Normative references... 9
3 Terms and definitions... 10
4 General... 10
5 Construction... 14
6 Verification and tests... 17
7 Marking... 19
Annex A (Normative) Supplementary requirements for entries... 20
1 Scope
This document specifies the design, construction, and testing requirements for Ex
equipment and Ex Components with dust ignition protection by enclosure “t”.
This document is applicable to electrical equipment protected by enclosure and surface
temperature limitation for use in explosive dust atmospheres.
This document does not apply to dusts of explosives, which do not require atmospheric
oxygen for combustion, or to pyrophoric substances.
This document does not apply to Ex equipment or Ex Components 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 document does not take account of any risk due to an emission of flammable or
toxic gas from the dust.
This document is a supplement and modification to the general requirements of GB/T
3836.1.When the requirements of this document conflict with the requirements of
GB/T 3836.1, the requirements of this document take precedence.
2 Normative references
The contents of the following documents, through normative references in this text,
constitute indispensable provisions of this document. Among them, for dated references,
only the edition corresponding to that date applies to this document. For undated
references, the latest edition (including all amendments) applies to this document.
GB/T 197 General purpose metric screw threads - Tolerances (GB/T 197-2018, ISO
965-1.2013, MOD)
GB/T 3836.1 Explosive atmospheres - Part 1.Equipment - General requirements
(GB/T 3836.1-2021, IEC 60079-0.2017, MOD)
GB/T 4208 Degrees of protection provided by enclosure (IP code) (GB/T 4208-2017,
IEC 60529.2013, IDT)
GB/T 4942.1 Degrees of protection provided by the integral design of rotating
electrical machines (IP code) - Classification (GB/T 4942.1-2006, IEC 60034-
5.2000, IDT)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 3836.1, as
well as the following definitions, apply.
3.1
Dust ignition protection by enclosure “t”
Type of protection for explosive dust atmospheres where electrical equipment is
provided with an enclosure providing dust ingress protection and a means to limit
surface temperatures.
4 General
4.1 Levels of protection
Type of protection “t” is divided into three Levels of Protection based on the risk of the
Ex equipment becoming an ignition source in an explosive dust atmosphere. The
equipment with dust ignition protection by enclosure “t” shall be either.
4.2 Equipment groups and ingress protection
The relationship between the level of protection, the equipment group, and ingress
protection (IP) is shown in Table 1.
4.3 Requirements for Ex equipment with level of protection “ta”
4.3.1 Fault current
Ex equipment not marked as specified in Clause 7 shall only be connected to circuits
with an expected short-circuit current not exceeding 1.5 kA.
4.3.2 Maximum surface temperature
The following requirements are modifications and additions to the requirements of
GB/T 3836.1.
4.3.3 Overpressure
An internal pressure of 4 kPa shall be applied to the enclosure in accordance with
6.1.1.3 prior to the dust exclusion test.
4.3.4 Dust exclusion
Group IIIC Level of Protection Group IIIB Group IIIA
Test of dust exclusion by enclosure shall be carried out in accordance with 6.1.1.
4.3.5 Protective devices
4.3.6 Internal supplementary enclosure
If the equipment contains components that generate arcs and sparks, then these
components shall be equipped with supplementary enclosures within the main
enclosure. In accordance with the provisions of 4.3.2, the maximum surface
temperature of the enclosure is used to determine the marked surface temperature of the
equipment.
4.4 Requirements for Ex equipment with Level of Protection “tb” and “tc”
4.4.1 Fault current
For Ex equipment with Level of Protection “tb” and “tc”, which is used for power
connection and can cut off fault currents above 10 kA, the maximum short-circuit
current shall be determined. The test is carried out in accordance with 6.1.1.1.It shall
be marked in accordance with Clause 7.
4.4.2 Maximum surface temperature
The maximum surface temperature shall be measured on the external surfaces of the
enclosure for Ex equipment with levels of protection “tb” and “tc" in accordance with
6.1.2 under normal operating conditions.
4.4.5.2 Thermal protective devices
The Ex equipment shall be protected by one or more integral thermal protective devices.
Thermal protective devices shall not be of a self-resettable type and shall be duplicated
unless conforming to GB/T 9364 (all parts), GB/T 9816.1 or ANSI/UL 248 (all parts),
in which case only one device is necessary.
5 Construction
5.1 Joints
5.1.1 General
All joints in the structure of the enclosure, whether permanently closed or designed to
be opened from time to time, shall fit closely together within the tolerances specified in
the documentation. They shall be effectively sealed against the ingress of dust and shall
comply with the following particular requirements and be subjected to the test of 6.1.1.
The use of grease alone to maintain the integrity of the seal is not considered to satisfy
this requirement.
5.1.4 Cemented joints
Cemented joints shall not be used on mating parts which need to be removed to gain
access to field wiring connections or in-service adjusting facilities.
5.1.5 Operating rods, spindles and shafts
Openings in enclosures for operating rods, spindles or shafts shall have means to inhibit
the ingress of dust, other than only grease or compound, both when the spindles, rods
or shafts are in motion and when they are at rest.
5.1.6 Windows
5.2.2 Entries
5.2.2.1 Plain entries
The clearance holes for plain entries shall have a diameter not more than 0.7 mm greater
than the nominal diameter of the entry thread gland or fitting. The inside of the
enclosure shall be provided with sufficient room to attach a locknut to the gland or
fitting.
5.2.2.2 Threaded entries
Threaded entries are considered to meet the requirements for Ex equipment with levels
of protection “ta”, “tb” and “tc” if they are.
6 Verification and tests
6.1 Type tests
6.1.1 Tests for dust exclusion by enclosures
6.1.1.1 General
Samples of the Ex equipment shall be subjected to the endurance to heat, endurance to
cold and impact tests specified in GB/T 3836.1 and the drop test if applicable. If there
is a supplementary enclosure, there shall be no visual damage to the supplementary
enclosure caused by the impact testing of the equipment enclosure.
6.1.1.2 Impact test for supplementary enclosures
The impact test for supplementary enclosures shall be performed in accordance with
the resistance to impact test of GB/T 3836.1 using the 1 kg mass dropped from a height
of 0.2 m. There shall be no damage which invalidates the type of protection.
6.1.1.3 Pressure test
Internal pressure shall be at least the following values for a duration of 60 0+10 s.
6.1.1.4 IP test
According to the requirements of Table 1, according to the provisions of GB/T 3836.1
on the ingress protection (IP) of the enclosure, the IP test shall be carried out for samples
with different levels of protection. It shall meet the following modified requirements.
6.1.2 Temperature tests
For level of protection “ta”, “tb” and “tc” the test shall be carried out as described in
GB/T 3836.1.
6.2 Routine tests
There are no additional routine tests required for levels of protection “ta”, “tb”, or “tc”.
7 Marking
The following requirements supplement the requirements of GB/T 3836.1, which are
applicable to Levels of Protection "ta", “tb” and “tc”. The symbol for the Level of
Protection shall be “ta”, “tb”, or “tc”.
......
Source: Above contents are excerpted from the full-copy PDF -- translated/reviewed by: www.ChineseStandard.net / Wayne Zheng et al.
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