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GB 16840.2-1997 PDF in English


GB 16840.2-1997 (GB16840.2-1997) PDF English
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GB 16840.2-1997: PDF in English

GB/T 16840.2-1997
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 130.220
C 82
GB 16840.2-1997
Technical Determination Methods for Electrical Fire
Cause - Part 2: Residual Magnetic Method
ISSUED ON: JUNE 03, 1997
IMPLEMENTED ON: MAY 01, 1998
Issued by: State Bureau of Technical Supervision
According to the Standardization Administration of China Announcement
No.7 of 2017, it is converted into recommended standard
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Definitions ... 4
3 Principle ... 4
4 Apparatus ... 5
5 Method Procedures... 5
6 Judgment ... 7
7 Written Procedures to be Followed during Inspection and Appraisal ... 8
Technical Determination Methods for Electrical Fire
Cause – Part 2: Residual Magnetic Method
1 Scope
This Standard specifies definitions, principles, apparatus, method procedures,
judgments, and written procedures to be performed during inspection and appraisal.
This Standard is applicable to determine the occurrence of short-circuit and lightning
based on data of residual magnetism under the condition that melted mark induced by
short-circuit and lightning cannot be found at the fire site of the fire point when
investigating the cause of electrical fires; and further analyze relationship with the
cause of the fire.
2 Definitions
For the purpose of this Standard, the following definitions apply.
2.1 Data of residual magnetism
The magnetic value that the ferromagnetic body retains after being magnetized by the
magnetic field formed by the short-circuit current of the wire and the lightning current.
The unit is millitesla (mT).
2.2 Melted mark induced by lightning
The melted marks that are formed on the surface of metal by the high temperature of
lightning.
2.3 Residual magnetism in conducting wire short circuit caused by fire burning
The magnetism of the ferromagnetic body that is maintained after being magnetized
by the magnetic field that is formed by the short-circuit of copper-aluminum wire that
is charged under high-temperature of fire.
3 Principle
Due to the magnetic effect of the current, a magnetic field is generated in the space
around the current; and the ferromagnetic body in the magnetic field is magnetized.
When the magnetic field escapes, the ferromagnetic body still maintains a certain
degree of magnetism.
5.2.1 Location
As the test specimen, it shall be taken from the fire point or around the wire of the fire
part that has been confirmed on the site. The distance between the specimen and the
wire should not exceed 20mm; but for the site with the possibility of thunder and
lightning, it may be extracted according to the actual situation; and it is not restricted
by the location.
5.2.2 Taking photos
Before extracting the samples, take photos on the site. The method of taking photos
may be divided into two items, namely, the orientation of the specimen and the close-
up of the specimen.
5.2.3 Extraction
--- Specimens that are fixed on walls or other objects shall not be bent, beaten, or
dropped during extraction;
--- Specimens with lower fire temperature should be extracted;
--- Specimens that are located near the magnetic material shall not be extracted;
--- When it is confirmed that the line has been short-circuited in the past, it shall not
be extracted;
--- If it is inconvenient to extract, it may be tested at the original location of the
specimen.
5.3 Storage
The extracted specimens should be put in a sampling bag for safekeeping; and the
specimen name and extraction location shall be indicated; and shall not be mixed with
magnetic materials or other objects.
5.4 Measurement
5.4.1 Dirt removal
Use water and solvent to remove carbon dust and dirt on the specimen surface before
measurement.
5.4.2 Preparation for measurement
According to the instructions of the instrument, turn on the power of the instrument,
and get ready after calibration and preheating.
5.4.3 Operation
The residual magnetism at the tip of the lightning rod is not large, namely, 0.6~1.0mT.
The data of residual magnetism for stray iron parts, nails, rebars, and metal pipes in
the lightning channel are all between 1.5 and 10mT. The above-mentioned data are
obtained from experiments and on-site lightning detection, and may be used as a
reference for judgment.
6.2 Comparison judgment
It is judged by comparison on the site that if there are lines passing through the same
two facilities, but one has residual magnetism and the other has not, it proves that the
wire with the residual magnetism has been short-circuited.
6.3 Judgment of magnetization law
The strength of ferromagnetic body magnetism is related to the distance from the wire
(short circuit). The closer to the wire, the stronger the magnetism. If the law from strong
to weak can be found during measurement, and then combined with the measured
data, it may be further determined whether the wire has been short-circuited.
6.4 Judgment of the residual magnetism in conducting wire short circuit caused
by fire burning
If conducting wire short-circuit caused by fire burning, it shall also generate a magnetic
file and keep the ferromagnetic body magnetic. To determine whether the short-circuit
is formed before the fire or the short-circuit is formed by fire burning, the fire source
shall be checked, and the judgment shall be made according to the actual situation of
the site.
7 Written Procedures to be Followed during Inspection
and Appraisal
7.1 When submitting the inspection, the inspection organism shall first fill in the
application form for the technical appraisal of the cause of electrical fire, which includes
the name, address, contact person of the organism applying for appraisal; name of the
unit that catches fire, sample name, quantity, sampling location, sampler, and purpose
of appraisal.
7.2 The appraisal unit shall fill in the sample receipt, task list, reception record and
original record after accepting the appraisal task.
7.3 After the completion of the appraisal, fill in the appraisal conclusion in the appraisal
report approval form, signed by the person in charge of the laboratory, and report to
the leader for approval after the quality review is correct.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.