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Classification of Dusts Relative to Electrical Equipment in Class II Hazardous Locations (1982) / Chapter Skim
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Appendix C: Electrical Resistivity
Pages 43-48

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From page 43...
... RECOMMENDED METHOD OF ME: ASUREMENT OF DUST RE SI STIVITY Scope The objective of this test method is to provide a convenient, albeit not precise, determination of the resistivity of dust layers for the purpose of ~ ~ The results are used to determine whether dusts nave res~st~v't~es similar to metallic dusts or to agricultural dusts; therefore, minor differences in measurement technique and experimental conditions are not likely to lead to differences in classification. Classitying dusts with regard to Dire and explosion nazaras.
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From page 44...
... If metallic dusts with oxidized surfaces are being measured the voltage gradient applied to the cell should be higher than the highest voltage gradient to which the dusts may be exposed in use (see page 71~. Preparation of Dust Sample The sample should be dry sieved through a 200-mesh sieve to exclude large particles and should be representative of dust that may deposit on the surface of electrical apparatus.
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From page 45...
... 5. If Ro is less than 10 Rs, dust resistivity should be computed from the equation: p R Ro HW R -R L 0 s VALIDATION OF TEST METHOD Since there is no data base for the recommended test method for determining electrical resistivity of dust, two panel members constructed three different test cells and tested four dusts (cornstarch, powdered sugar, activated charcoal, and powdered graphite)
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From page 46...
... 1644A Megohm Bridge at 500 volts dc; Test Cells 1 and 2, testing activated charcoal and graphite, used Fluke digital ohmmeter. Test Cell 3, testing charcoal and graphite, used Triplett multimeter.
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From page 47...
... 47 REFERENCES Instrument Society of America, Area Classification in Hazardous Dust Locations, Report ISA-S12. 10, Pittsburgh, Pennsylvania, 1973.
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Key Terms

  • test cell
  • powdered sugar
  • instrument society
  • test cells
  • test method

  • activated charcoal
  • cell dimensions
  • voltage gradient
  • dust resistivity
  • recommended method

  • various conditions
  • electrical resistivity
  • metallic dusts
  • bars approximately
  • powdered graphite

  • placed approximately
  • method proposed
  • dust samples
  • excessive error
  • measurement technique

  • convenient instrumentation
  • filled sample
  • electrodes similar
  • chamber tapped
  • cell resistance

  • determining electrical
  • power supply
  • rectangular electrodes
  • megohm bridge
  • measured resistance


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