1 HVACR317 – Refrigeration Safety and Hazard Prevention.
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Transcript of 1 HVACR317 – Refrigeration Safety and Hazard Prevention.
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HVACR317 – Refrigeration
Safety and Hazard Prevention
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Safety and Hazard Prevention• Current is the killing factor in electrical
shock.• The human body has resistance; if
voltage is applied, current will flow through the human body.
• If one tenth of the current required to operate a 10 watt light bulb passed through your chest, the result could be lethal.
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Diagram of Path of Electricity 1
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Diagram of Path of Electricity 2
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Diagram of Path of Electricity 3
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Effects of Current on the Body• A current of 2 to 3 mA (milliamps) will
cause a tingling sensation.• Milliamps is 1/1000th of an amp.• The tingling sensation increases and
becomes very painful at about 20 mA.• Currents between 20 – 30 mA will
cause muscle contraction.• At this voltage, you may not even be
able to release the wire you are holding.
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Effects of Current on the Body
• Currents between 30 – 60 mA will cause muscle paralysis and difficulty breathing.
• Currents at 100 – 200 mA will generally cause death.
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Lockout / Tagout Procedures
• One of the best ways to prevent electric shock is to follow safety precautions such as Lockout/Tagout procedures.
• Equipment that is being worked on should be disconnected from the power source and locked.
• See the following slide for equipment used in the lockout/tagout procedure.
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Lockout / Tagout Materials
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Lockout / Tagout Procedures
• The person working on the equipment should be the one to carry the only key.
• This will prevent accidental activation of the equipment.
• The power supply should be tagged with:− the name of the person working on it.− what service is being performed.− the reason for the service.− the date and time of the service.
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Basic Safety Tips
• Never work alone.• Learn first aid.• Do not wear jewelry at work.• Be careful using screwdrivers on
electrical panels.
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Tips Regarding Portable Electrical Tools• Electric tools with metal frames should
have a grounding cord.• The grounding wire will protect the
operator from electric shock by carrying the current to ground.
• This lets the breaker or fuse trip the circuit.
• NOTE: The grounding adapter must be connected to a ‘good’ ground.
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Example of Grounded Electric Tool
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Non-Conducting Ladders
• Metal or aluminum ladders are conducting ladders; they can be hazardous when working near electricity.
• Non-conducting ladders are those made of fiberglass or wood.
• These will protect technicians from a shock to ground.
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The Safety Ground Wire
• The equipment grounding wire is added for safety purposes; it is called the safety ground.
• The safety ground is required by the National Electric Code (NEC) on all systems.
• The color code for this wire is green or bare copper.
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The Safety Ground Wire
• The safety ground (aka Chassis Ground) connects to the same terminal as the neutral wire at the service panel.
• The safety ground only carries current in the event of a short circuit.
• The safety ground wire is connected to the frame of a motor or appliance.
• This provides an alternate pathway for electrons to go to ground and not through a technician.
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The Neutral Wire
• The earth is always at zero potential (no voltage).
• The earth can be used to complete an electrical circuit.
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The Neutral Wire
• Many electrical devices operate with just one ‘hot’ wire and another one called neutral.
• This is also known as “single-phase.”• A potential difference exists because the
hot wire has voltage and polarity.• The “neutral” wire is connected to earth
(grounded), which is zero voltage.
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The Neutral Wire
• The hot wire usually has black insulation.
• The hot wire can be another color except white or green, for ease of identification.
• The neutral wire has white insulation for ease of identification.
• The neutral wire is connected to a solid copper rod (driven 8 feet into the ground).
• The copper rod is called a “grounding electrode.”
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The Neutral Wire
• The grounded neutral wire has zero voltage.
• A zero volt reading will be found from the white wire to ground.
• A 120V reading will be found from the hot wire to neutral or ground.