understanding nec and nema for locations with ......nema ratings provisions in nec that allow the...
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Understanding NEC and NEMA for Locations with
Combustible Dust
Karl von KnobelsdorffKnobelsdorff Electric
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Understand the Unique Hazards in our Industry
NEC Hazardous Location Classifications
Ignition Sources
NEMA Enclosure Types and Examples
Scope and Purpose
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National Fire Protection Association
Planning and Design to Reduce Risks
Explosion Suppression
Electrical Hazards Facing all Facilities
Scope and Purpose
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Industrial Solvent
Made from combining Propane and Nitric Acid
Used in Dry Cleaning
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Hazards are known
Safety is Priority
Rules keep People Safe
Safety in Motorsports
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OXYGEN
OXYGEN
FUEL
FUEL
IGNITION DISPERSION
CONFINEMENT
IGNITION
Hazards in the Grain Industry
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Grain Dust
Enclosed Building
Spark or Heat
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Hazardous Classifications
NFPA 70: National Electrical Code (NEC)
Chapter 5 Special Occupancies
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Hazardous Classifications
Class:The type of material or substance presenting a hazard
Class I – Gas or VaporsClass II – Dust or ParticlesClass III – Lint or Fibers
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Hazardous Classifications
Divisions:Probability of a hazardous material being present
Division 1 - During Normal Operating ConditionsDivision 2 - Not Likely in Normal Operating Conditions
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Hazardous Classifications
Class I Division 1:Gases exist under normal conditionsGases exist due to faulty operations
Class I Division 2:Gases or Liquids can only be released by rupture or breakdownFailure of ventilation equipment
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Hazardous Classifications
Class II Division 1: High concentrations of dust are present during normal conditions(explosive levels)
Class II Division 2:Normal conditions do not present high levels of combustible dust
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Hazardous Classifications
Class III Division 1:Locations where easily ignited fibers are used or manufactured
Class III Division 2:Locations where easily ignited fibers are stored or handled
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Hazardous Classifications
Groups:Define the type of hazardous material in the area
Groups A – D: Various Gasses & VaporsGroup E: Metals (exotic / fine particles)Group F: Carbon Black / Coal DustGroup G: Grains / Starch / Flour / Wood
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Hazardous ClassificationsClassification Zones: Based on Hours Per Year
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Hazardous Classifications
Material Concentration Required for Explosion
Saw Dust - 40 g/m3Corn Dust – 60 g/m3Wheat / Starch – 30 g/m3Sugar Dust – 200 g/m3
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Common Locations
Receiving
Batching Scales/Mixers
Bindecks
Loadout
Explosive Grain Dust
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Housekeeping
Have Plan in Place
Secondary Explosions
Thickness of Dust Layer
1/8” or more of dust and you have a serious hazard for secondary expolosion
Explosive Grain Dust
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MotorsTotally Enclosed, Fan-Cooled (TEFC)Explosion Proof (EXP)
Ignition Sources
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Control DevicesPosition SwitchesSolenoidsTemperature Transmitters
Ignition Sources
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Light fixtures & PowerArea LightingEmergency LightingReceptacles
Ignition Sources
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Powered Industrial Equipment
Hazard Monitoring (HazMon)BearingsRub BlocksSpeed Sensors
Ignition Sources
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Explosion Proof Devices
Contains the Explosion
Listed for the Hazardous Area
Engaged Threads
Ignition Sources
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National Electrical Manufacturers Association (NEMA)
Type 1: Indoor useType 3: Outdoor use (Water Tight, Dust Tight)Type 4/4X: Indoor or Outdoor Use (Dust Tight)Type 7: Indoor use (explosion-proof) Class 1 and 2Type 9: Indoor use (dust-ignition proof) Class 2
NEMA Ratings
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Type 1: Indoor use
Non Hazardous Locations
NEMA Ratings
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Type 3: Outdoor Use
“Dust Tight”
3R - “Weather Tight”
NEMA Ratings
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Type 4/4X: Indoor or outdoor use
“Dust Tight”Class 2 Division 2
NEMA Ratings
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Type 7: Explosion-proof
Contains the Explosion
Class 1, Division 1 & 2
NEMA Ratings
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Type 9: Dust-ignition proof
Not as Common
Class 2, Division 1 & 2
NEMA Ratings
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NEMA 3
GFCI where required
NEMA Ratings
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NEMA 3
Gasketed
Designed to keep out water and dust
NEMA Ratings
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NEMA 3
Faulty Cover: Spring Malfunction
NEMA Ratings
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NEMA 3 Outdoor
NEMA 4 Dust Tight
Look for sticker inside
NEMA Ratings
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NEMA 4 “Dust Tight” Junction Box
NEMA 7 “Explosion Proof"Light Fixture”
NEMA Ratings
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Provisions in NEC that allow the mixing of NEMA 3, 4, 7, & 9 equipment
NEC – Chapter 5Boxes containing taps, joints, or terminal connections, in addition to being dust tight, must be provided with threaded hubs and must be identified for use in Class II locations
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Mixing of NEMA 3, 4, 7, & 9 enclosures
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Know the location
Look for Motor Plate Info
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Dual Listed Motor
Temperature Code
T3B: Max Temp = 329 degrees F
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Know the Motor Plates
Different designs for each manufacturer
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Not Dual Listedon motor tag
Class 1, Division 2Class 1, Zone 2
TEFCNeed to Look Deeper
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More Motor Plate Info
Document while clean
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NEMA 7 “Explosion Proof”
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Class 2 Division 1
Covers installed
Ventilation
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NEMA 9“Dust Ignition Proof”
2-stage Receptacle
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NEMA 9“Dust Ignition Proof”
Spring Cover
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NEMA 9“Dust Ignition Proof”
Start/Stop Switch
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Reduce Risk During Design Phase
Classify Hazardous Locations
Lowering Risk and Cost
Design with Safety in Mind
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Hazard Management: Mitigation & Analysis
•Facilities/Structures•Conveying Equipment•Process Equipment•Dust System Equipment•Ventilation & Isolation
National Fire Protection Association
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Management Systems
•Procedures and Practices• Inspection, Testing & Maintenance•Training & Hazard awareness
National Fire Protection Association
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Hazard Identification & Design OptionsHazard Management: Mitigation & PreventionHousekeeping Methodology & ProceduresIgnition Source ControlPPEExplosion Segregation and SuppressionExample Dust Hazard Analysis
National Fire Protection Association
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Facility/System DesignDust Handling Area SegregationEquipment Explosion Assessment•Storage•Material transfer Systems•Dust Collection/Vacuumed SystemsCleaning MethodsIgnition Sources and Fire Protection
National Fire Protection Association
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Dust Hazard Analysis (DHA)
Review of a facility for potential fire or explosion hazards
Prioritize and generate plans to manage risk
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Concrete Mills
Minimize dust ledgesElectrical conduit can be cast into the wall
Steel tubes minimize ledges on floor steelConduit can be imbedded into the floor
Building Design
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Steel Mills
Interior liner panels conceal girts
Tube steel and solid floorsCheckered plate helps segregate dirty areas
Building Design
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Venting
Pressure Relief Venting•Legs•Filters
Hazardous Areas• “H” occupancy•Pressure relief panels•Louvers
Building Design
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THE BACKUP PLAN:
Flame-arresting and particulate retention vent system
Explosion Suppression System
Building Design
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Design Out the Hazards
Goal is to Not wear PPE
Keep employees out of harms way
Electrical Hazards
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30,000 Arc Flash Incidents Per Year• 7,000 Burn Injuries• 2,000 Hospitalizations• 400 Fatalities
80% of fatalities due to burns, not electrical shock
81 Electrocutions in 2015• 40% at 250 volts or less
Electrical Hazards
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Design Out the Hazards
Remote Mains
Smart MCCS
HMI/SCADA for troubleshooting
Electrical Hazards
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Hazardous Locations
Class 2, Division 1 and 2
Ignition Sources
NEMA Types and Ratings
Conclusion - Review