Fundamental rule of protection

The fundamental rule of protection against electric shock is provided by the document IEC 61140 which covers both electrical installations and electrical equipment.
Hazardous-live-parts shall not be accessible and accessible conductive parts shall not be hazardous.
This requirement needs to apply under:

• Normal conditions, and
• Under a single fault condition

Various measures are adopted to protect against this hazard, and include:

• Automatic disconnection of the power supply to the connected electrical equipment
• Special arrangements such as:

  - The use of class II insulation materials, or an equivalent level of insulation
  -  Non-conducting location, out of arm’s reach or interposition of barriers
  -  Equipotential bonding
  -  Electrical separation by means of isolating transformers