Element 5

Question 1

Identify the basic parameters of an electrical system?

Answer 1

• Voltage.
• Current.
• Resistance.

Question 2

List the hazards of electricity?

Answer 2

• Electric shock.
• Burns (direct and indirect).
• Fire and explosion.
• Arcing and secondary effects.

Question 3

Identify some effects when somebody receives an electric shock?

Answer 3

• Mild discomfort.
• Muscle tremor.
• Uncontrollable muscle contractions.
• Respiratory failure.
• Ventricular fibrillation.
• Cardiac arrest.
• Severe burns.

Question 4

Outline the factors that will influence the severity of any injury sustained from electricity?

Answer 4

• System voltage.
• Duration of contact.
• Pathway through the body.
• Body resistance.
• Contact surface area.
• Environmental factors.
• Frequency.

Question 5

List the reasons why portable electrical equipment is often involved in electrical accidents?

Answer 5

• Frequently unsuitable for the job being done.
• Misuse.
• Not inspected.
• Not maintained.

Question 6

Outline some high-risk work activities involving electricity?

Answer 6

• Using poorly maintained electrical equipment.
• Working near overhead power lines.
• Contact with underground power cables.
• Working on live supplies.
• Using electrical equipment in wet environments.

Question 7

Draw a simple equation to illustrate Ohm’s Law?

Answer 7

Voltage = Current x Resistance
Volts = Amps x Ohms
V = I x R

Question 8

Identify the 2 types of current ?

Answer 8

• Direct Current (DC).

- Alternating Current (AC).

Question 9

What is the mains electricity supply in the UK?

Answer 9

• 230 volts (50 hertz).

Question 10

Explain the meaning of “Live” and “Dead”?

Answer 10

• When a system is connected to an electrical power source it is described as “Live” (in some countries it is described as “Hot”).
  Once it has been disconnected from its power source it might be described as “Dead”.

Question 11

Define “Direct” electrical burns?

Answer 11

Where a CURRENT causes overheating as it passes through the skin and internal tissues of the body.

Question 12

Define “Indirect” electrical burns?

Answer 12

Does not occur as a result of a current passing through the body, but when an electrical accident causes something to overheat and explode.

Question 13

Outline how electricity can causes fires?

Answer 13

• Electrical equipment may be faulty, then overheat and results in a fire.
• The system may be overloaded as too much current passes through it, resulting in overheating and fire.
• Equipment may be misused (bare wires into socket rather than plug).
• A flammable atmosphere may be present.
• Electrical equipment may produce heat or sparks as a natural function (a fan heater produces heat).
• Poor internal connections.

Question 14

List the main risks associated with “Arcing”?

Answer 14

• Electric shock as a result of being struck by the arc.
• Direct burns as a result of being struck by the arc.
• Indirect burns from the radiant heat given off by the arc and from the melting of any equipment.
• Damage to the eye as a result of the ultraviolet (UV) light that is emitted from the arc.

Question 15

Identify conditions and practices likely to lead to accidents involving electrical equipment?

Answer 15

• Using unsuitable equipment (I.e using non intrinsically safe equipment in a flammable atmosphere).
• Using equipment in wet, damp or humid conditions.
• Misuse.
• Physical abuse.
• Repairs carried out by unauthorised personnel.
• Continued use of damaged or faulty equipment.
• Chemical damage to the flex.
• Lack of routine inspection, testing or maintenance.

Question 16

Outline some control measures to be considered when selecting portable electrical equipment for use on a construction site?

Answer 16

• Consider the use of battery powered equipment.
• Consider the use of reduced and low voltage (110v) equipment centre tapped to earth.
• Provide increased protection through the use of RCD.
• Locate cables carefully, away from hazards.
• Consider the use of double insulated equipment.
• Carry out pre-use checks of the equipment for signs of damage.
• Train operators in safe use of equipment.
• Avoid using in wet conditions.
• Implement a programme of routine visual inspection and thorough testing of electrical equipment and cables.

Question 17

Identify the various protective systems that can be used for electrical equipment?

Answer 17

• Fuses.
• Earthing.
• Isolation.
• Double insulation.
• Residual current devices.
• Reduced low voltage.

Question 18

Outline the hazardous environments that you may protect electrical equipment against?

Answer 18

• Weather.
• Natural hazards (solar radiation, plants, animals).
• Extremes of temperature (heat from motors).
• Dirty conditions.
• Corrosive conditions.
• Liquids and vapours (splashing, immersion).
• Flammable substances.

Question 19

Outline the advantages of fuses?

Answer 19

• They are cheap and reliable.

- They offer a good level of protection for electrical equipment against current overload.

Question 20

Outline the limitations of fuse?

Answer 20

• They primarily protect equipment rather than people.
• A fuse does not stop current flow quickly enough to prevent ventricular fibrillation (fatal injury).
• They are easy to bypass.

Question 21

Outline some advantages of earthing?

Answer 21

• Protects the person from fatal electric shock.

- Often provides secondary protection to the equipment.

Question 22

Outline the limitations of earthing?

Answer 22

• A poor or broken earth connection will prevent the earth from working properly, and go completely undetected.
• It is easy to disconnect and disable.

Question 23

What is the advantage of isolation?

Answer 23

It is a very effective method of ensuring that people cannot be injured by electrical energy when working on an electrical system.

Question 24

What is the advantage of Double insulation?

Answer 24

• It relies on insulation rather than the electrical system itself for safety.

Question 25

What is the limitation of Double insulation?

Answer 25

- The insulation must be routinely visually inspected because there is no earth protection.

Question 26

What does RCD stand for?

Answer 26

Residual Current Device

Question 27

Define the principle of an RCD?

Answer 27

- It constantly compares the amount of current flowing down the live and neutral lines. If an imbalance is detected, it trips the circuit.

Question 28

Give an advantages of RCDs?

Answer 28

- Excellent protection for people in the event of electric shock.

Question 29

Give some limitations of RCDs?

Answer 29

- They do not provide over-current protection. - They have to be tested periodically to ensure that they are still working effectively. - They can cause repeated circuit tripping if there is a fault, which can encourage people not to use them or to disable them.

Question 30

List the emergency procedures which should be followed, when dealing with an electric shock casualty?

Answer 30

- Do not touch them. - Call for help. - Turn off the power supply. - Call for an ambulance. - If the power supply cannot be switched off then carefully push or pull the casualty away from the live part using non-conducting material such as timber or dry clothing. - Check breathing: if breathing place in recovery position, if not, then apply CPR. - Treat any obvious burns. - Treat for physiological shock. - Make sure they get professional medical treatment.

Question 31

Identify the things to check during a routine visual inspection of a portable appliance?

Answer 31

- The body of the plug is intact and secure. - The outer sheath of flex covers inner cores into body of plug. - The plug cable clamp appears to be tight. - The flex appears fully insulated, with no splits or severe kinks/pinches. - The body of the appliance is intact. - The outer sheath of flex covers inner cores into body of appliance. - The appliance cable clamp appears to be tight. - No obvious scorch marks to plug or appliance body. - The plug and appliance are not excessively soiled. - The plug and appliance are not wet.

Question 32

Outline the factors that influence the frequency of inspection and testing of electrical appliances?

Answer 32

- Legal standards and codes of practice. - Type of equipment and whether or not it is hand-held. - Manufacturers recommendations. - Initial integrity and soundness of the equipment. - Age of equipment. - Working environment in which the equipment is used or the likelihood of mechanical damage. - Frequency and duration of use. - Foreseeable abuse of the equipment. - Effects of any modifications or repairs to the equipment. - Analysis of previous records of maintenance, including both formal inspection and combined inspection and testing.

Question 33

What does PAT stand for?

Answer 33

- Portable Appliance Testing

Question 34

Give the advantages of PAT?

Answer 34

- Detection of faults not visible to the eye. - Early removal/repair of unsafe equipment. - Demonstration of legal compliance. - Trends or patterns of faults that may be spotted.

Question 35

Give some limitations of PAT?

Answer 35

- It provides proof of safety at one moment in time only. - It does not ensure safe use or prevent misuse. - Items may be missed and then remain untested. - It cannot be applied to all equipment (computers).

Question 36

What is the relationship called, that links Voltage, Current and Resistance?

Answer 36

- Ohm's Law