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Element 11 cheat sheet: Electricity

Written by Imran Qureshi (NEBOSH)

Full notes for Element 11

11.1 Hazards and risks

  • Electric shock occurs when current passes through the body.
    • ('text', 'Electric shock occurs when current passes through the body.')
  • Severity depends on voltage, frequency, duration of contact, body resistance (wet skin lowers it) and the path the current takes through the body.
    • ('text', 'Severity depends on voltage, frequency, duration of contact, body resistance (wet skin lowers it) and the path the current takes through the body.')
  • Incidents and electrical fires are likely when: equipment is unsuitable; inadequately maintained; defective or damaged; used in wet environments; or overheated (for example when charging portable equipment).
    • ('text', 'Incidents and electrical fires are likely when: equipment is unsuitable; inadequately maintained; defective or damaged; used in wet environments; or overheated (for example when charging portable equipment).')
  • Secondary effects include falls from height after a shock.
    • ('text', 'Secondary effects include falls from height after a shock.')

Tip: A small current through the heart can kill, so the path matters as much as the voltage.

11.2 Control measures

  • Protect conductors with insulation and enclosure; use equipment that is strong enough and suited to the job and place; and use competent people.
    • ('text', 'Protect conductors with insulation and enclosure; use equipment that is strong enough and suited to the job and place; and use competent people.')
  • Protective systems and their advantages and limits:
    • Fuses and circuit breakers (protect against overload and short circuit, not against shock)
    • Earthing (gives a safe path for fault current)
    • Isolation of the supply (the safest way to work on equipment)
    • Double insulation (no earth needed, but damage to the casing can expose live parts)
    • Residual current devices (cut the supply quickly in a fault, but they need testing and do not prevent all shocks)
    • Reduced and low voltage systems (they limit the voltage, and so the harm that a fault can cause)
  • Safe systems of work: no live working unless there is no alternative; isolate and lock off; locate buried services before digging; and protect against overhead lines.
    • ('text', 'Safe systems of work: no live working unless there is no alternative; isolate and lock off; locate buried services before digging; and protect against overhead lines.')
  • Inspection and maintenance:
    • User checks before use
    • Formal inspection and tests of installations and equipment
    • Frequency based on the risk
    • Records kept
    • Portable appliance testing (PAT), which has advantages (finds faults) and limitations (only shows the condition at the time and does not find all faults)

Tip: No single device is enough, so layer your protection.

Element 10