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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.