Comp TIA A Certification Essentials Mercy Vocational High School

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Comp TIA A Certification EssentialsMercy
Vocational High School

• Instructor Mr. Maphorisa
• 2007/2008

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Electrical Safety

• Note Electricity can be dangerous. If you dont
  follow proper safety precautions , electricity
  could kill you.
• Current can kill
• Current not voltage , is what causes the danger.
  Even a small amount of current passing through
  your heart can be sufficient enough to cause
  ventricular fibrillation or stop your heart
  entirely. A dangerous level of current is
  possible even with low voltage sources, such as a
  9 v battery.
• The 1-10 100 rule
• The 1-10-100 rule states that you can feel 1 mA
  (milliamp, or 1/1000 amp) of current through your
  body, 10mA is sufficient to make muscles contract
  to the point where you cant let go of a power
  source, and 100 mA is sufficient to stop your
  heart . This rule is a rule you should learn and
  respect.
• Calculating current
• Current, Voltage and resistance are related
  through the following formula

V ir
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Electrical Safety

• In this formula , V is voltage in volts (v) , I
  is current in amps (A) and r is the resistance in
  ohms. At a given voltage , current increases as
  resistance drops. A dangerous level of current
  can be reached if resistance is reduced
  sufficiently.
• Resistance of a human body
• The human body has resistance of about 500kOhms.
  This value is a somewhat ideal figure for contact
  with a small area of dry skin. Moisture and sweat
  on your skin will lower the resistance to a value
  nearer 5000 Ohms. Contact with a greater area of
  skin , e.g. gripping a wire btn your fingers or
  grasping a pipe, will further reduce resistance.
  If you were immerse your hand or foot , or
  puncture the skin so that the electrical
  connection is made with more conductive blood
  and tissue , the resistance could be a low as 100
  ohms.

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Safety Precautions

• You should always follow common sense safety
  precautions to avoid electric shock.
• Dont touch exposed electrical wires
• Touch only insulated handles and parts of tools,
  probes, cords and so forth
• Leave covers on equipment unless u need to access
  internal components.
• Work one handed. If you use one hand electricity
  is likely to flow through your body and possible
  cause electric shock or death.
• Never Insert anything on the wall outlets other
  than a power cord.
• Jewelry are prone to electric shock
• Keep your hands clean and dry.
• Dont work with electricity in wet surroundings,
  especially wet floors

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Electrical measurements
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Multimeters

• Multimeters are devices used to measure
• Current, resistance and voltage.
• The figure above shows an analog multimeter and a
  digital one.
• To measure each parameter you have to select the
  right setting using the dial in the middle of the
  meter.