1)Distinguish between different electric shock hazard mechanism:
-Firstly, the human body touches the charged part and at the same time touches the ground potential, or touches another charged part of a different potential hazard (direct contact hazard).
-Secondly, the danger of the human body touching an exposed conductive part of electrical equipment which has become electrically charged due to a break in the insulation and at the same time touching the ground potential, or touching another conductive part at a different potential, e.g. another exposed conductive part or an external conductive part (danger of indirect contact).
The two hazard mechanisms are undoubtedly premised on the basic criterion that the accessible part should not be a hazardous part under either normal or fault conditions.
2) Every piece of electrical equipment should have some protection against electric shock appropriate to the installation.
Shock protection can be provided by the environment, the equipment itself, the power supply system, or a combination of them, as shown in Table 1.
Indirect contact protection relies on the following complementary measures:
--Basic protection that can provide protection against electric shocks, provided that the failure of the basic protection is taken into account, and
--Additional protection that provides protection against electric shock when the basic protection fails.
This additional protection may be obtained by appropriate construction of the equipment (Class II) or by measures taken at the time of installation of the device (e.g., Class 0, I, III), or by a specialized combination of both.
This technical report divides the equipment into four categories according to indirect contact protection, and the most commonly used protective measures used in conjunction with them are summarized in Table 1.
By definition, an electric shock may produce pathophysiological effects on the person who receives it.
The methods of protection (basic protection plus additional protection) achieve the following:
- limiting the current flowing through the body to a non-hazardous level (e.g., categories 0, II, and III);
- limiting the Limit the duration of current flow through the body to a level that does not cause dangerous pathophysiologic effects in the body (e.g., Category I).
Note: Requirements for stationary equipment with no exposed conductive parts and at least basic insulation are under consideration.