Every electrical apparatus or machine consists of two distinct sections - one which carries the electricity, and other which is isolated (insulated) from the electric currents. The former may be called the `Live' side whiles the latter `Earth’ side. A person near about the apparatus or handling it can safely touch the Earth side, but not the live side, for obvious reasons. To ensure that the isolation of the two sections is effected properly, the apparatus is tested by subjecting it to a Voltage much higher than the normal working Voltage. If the insulation is good, it stands the test without breakdown otherwise high electrical stress punctures the insulation at its weakest spot foretelling a later calamity to unwary user. Government Department- when buying electrical equipments- and all reputable manufacturers test every piece of equipment by this test called HIGH VOLTAGE TEST. It weeds out poorly insulate apparatus.