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HVACR317 – Core for Refrigeration
Safety and Hazard Prevention
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Safety and Hazard Prevention
Current is the killing factor in electrical shock
Human bodies 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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Safety and Hazard Prevention
A current of 2 to 3 mA.
Will cause a tingling sensation
(The m stands for milli, A is for amps)
Milli is 1/1,000 of an amp
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Safety and Hazard Prevention
The tingling sensation increases and becomes very painful at about 20mA
Currents between 20 and 30 mA will cause muscle contraction
At 20 and 30 mA you may be unable to let go of the wire
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Safety and Hazard Prevention
Currents between 30 and 60 mA
Will cause muscle paralysis and difficulty breathing
Currents at 100 and 200 mA
Will generally cause death
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Safety and Hazard Prevention
Lockout – Tag Out Procedures
One of the best ways to prevent electrical shock
Equipment being worked on, should be disconnected from the power source and locked
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Safety and Hazard Prevention
The person working on the equipment should carry the only key
This will prevent accidental activation of the equipment
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Safety and Hazard Prevention
The Power Supply Should Be Tagged With
Name of the person working on the equipment
What service is being preformed
Reason for service
Date and Time
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Safety and Hazard Prevention
Safety Do not work alone
Learn first aid
Do not wear jewelry
Be careful using screwdrivers on electrical panels
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Safety and Hazard Prevention
Portable Electric Tools
Electric tools with metal frames should have a grounding cord
The grounding wire will protect the operator from electrical shock
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Safety and Hazard Prevention
Portable Electric Tools
The grounding wire will carry current to ground
This will let the breaker or fuse trip the circuit
The grounding adaptor must be connected to a good ground
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Safety and Hazard Prevention
Non – Conducting Ladders Metal or aluminum ladders
Can be hazardous
Non – Conducting ladders are made of fiberglass or wood
Will protect you from a shock to ground
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The Safety Ground Wire
The equipment grounding wire is added for safety purpose
It is called the safety ground
The safety ground is required by the National Electrical Code on all electrical systems
The color code for this wire is green or bare copper
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The Safety Ground Wire
The safety ground (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
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The Safety Ground Wire
This will provide an alternate
pathway for electrons to travel to ground and not through someone’s body
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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
Many electrical devices operate with just one hot wire and another wire called neutral
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The Neutral Wire
This is also called single phase
A potential difference exists because the hot wire has voltage and polarity
The “neutral” wire is connected to the 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
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The Neutral Wire
The neutral wire has white insulation ease of identification
The neutral wire is connected to a solid copper rod (driven eight 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 120 volt reading will be found from the hot wire to neutral or ground
