Accessible Part: What it Is, Definition, Meaning

Definition

The term ‘accessible part’ is officially defined within the IEC 60050-195-2021 as:

part that can be touched by means of the standard test finger.

IEC 60050-195-2021

IEC 60335-1 defined the term “accessible part” as follows:

part or surface that can be touched by means of test probe B of IEC 61032, and if the part or surface is metal, any conductive part connected to it.

IEC 60335-1-2020

Note 1 to entry: Accessible non-metallic parts with conductive coatings are considered to be accessible metal parts.

Note 2 to entry: IEC 61032 specifies the elements and dimensions of test probes designed to check that enclosures protect persons against access to hazardous parts and protect equipment against the ingress of external solid objects. Test probe B is a standard test finger.

Accessible Part Explanation

According to the fundamental rule of protection against electric shock established by IEC 61140, hazardous-live-parts must not be accessible and accessible conductive parts must not be hazardously live, neither under normal conditions nor under single fault conditions. Therefore, it is important to establish rules of accessibility of hazardous parts of electrical equipment under normal conditions to prevent persons from coming into contact with these parts, protecting them from electric shock and from mechanical injury.

The standard test finger used to simulate the human finger is shown in figure 1 of this article. It is a special test finger with a diameter of 12 mm and a length of 80 mm and has two joints. The standard test finger is designed to test enclosures of electrical equipment to ensure the IP2X degree of protection, which protects against finger access to hazardous parts.

Standard test finger
Figure 1. Standard test finger

Figure 1 shows:

  • 1 – Handle;
  • 2 – Guard;
  • 3 – Limiter;
  • 4 – Joints;
  • 5 – R2±0.05 cylindrical;
  • 6 – Insulating material;
  • 7 – Chamfer all edges;
  • 8 – R4±0,05 spherical.

Both joints shall permit movement in the same plane and the same direction through an angle of 90° with a 0° to +10° tolerance.

Examples of Accessible Parts

International standards refer to any part of electrical equipment that can be touched by a person’s finger as an accessible part. Any other part of the electrical equipment that can be touched by a person’s hand, foot, head or torso is all the more an accessible part. The formal accessibility test procedure prescribed by the requirements of international standards involves the use of a standard test finger, by which an average human finger is simulated.

The term “accessible part” is widely used in regulatory requirements for protection against electric shock. Parts are considered non-accessible if they are enclosed in an enclosure which has a degree of protection of at least IP2X as required by IEC 60529. Such an enclosure normally prevents a finger touching hazardous parts of electrical equipment.

All other parts of the electrical system are considered accessible parts which should not constitute a hazard to humans or animals under normal conditions. In the event of single or multiple faults, some accessible parts, e.g. exposed conductive parts, may be subject to hazardous touch voltages. In the electrical installation of buildings, measures are therefore taken to reduce these voltages, e.g. by equipotential bonding. The period of time during which class I faulty electrical equipment operates can also be reduced to a safe value, e.g. by automatically disconnecting the power supply.

References

  1. IEC 60050-195-2021
  2. IEC 60335-1-2020
  3. IEC 61032

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