Hazardous-Live-Part: Defininition, Meaning, Examples

Hazardous-live-part: a live part that, under certain conditions, can give a harmful electric shock [defined in the IEC 60050-195-2021].

Note 1 to entry: A hazardous voltage can be present on the accessible surface of solid insulation. In such a case, this surface is considered to be a hazardous-live-part .

BS7671 provides the following definition: a live part which can give, under certain conditions of external influence, an electric shock.

Hazardous-live-parts shall not be accessible and accessible-conductive-parts shall not be hazardous live either:

  • under normal conditions (operation in intended use, see 3.6 of ISO/IEC Guide 51:2014, and absence of a fault); or
  • under single-fault conditions.

NOTE. The accessibility rules for ordinary persons can differ from those for skilled or instructed persons and can also vary for different products and locations.

For high-voltage installations, systems and equipment, entering the danger zone is considered the same as touching hazardous-live-part.

Hazardous-Live-Part Examples

By means of the term “hazardous-live-parts” those parts from the whole variety of live parts are distinguished, whose contact with which can be accompanied by an electric shock hazard for humans and animals. Under normal conditions, live parts are considered to be hazardous-live-parts if they are exposed to voltages in excess of extra-low voltage, i.e. hazardous-live-parts exceeding 50 VAC and 120 VDC. However, many regulations specify lower voltages.

For example, IEC 60950-1 specifies that for dry conditions and a contact area equivalent to a human hand, steady-state AC voltages up to 42.4 V amplitude or up to 60 V DC are generally not considered hazardous.

IEC 61558-1:2017 does not classify as hazardous-live-parts that are separated from the power supply by means of double or reinforced insulation and are exposed to AC voltage up to 35 V amplitude or up to 60 V DC without pulsation. The standard also specifies that the voltage on live parts may exceed these values, but under these conditions the AC and DC touch currents must be less than 0.7 mA amplitude and 2.0 mA, respectively.

In rooms of the building with unfavorable conditions (damp and wet rooms, rooms with conductive floors, walls, ceilings, e.g. bathrooms, rooms with chemically active environment, etc.) and outside the building, live parts are not hazardous when they are under 50 VAC voltage, for example – to 12 V, and under 120 VDC voltage, for example – no more than 30 V.

To protect against electric shock, many electrical installations of buildings use class III electrical equipment, which has no hazardous live parts. The live parts of this electrical equipment are at extra-low voltages, which may be less than 50 VAC or 120 VDC. The rated voltage of class III electrical equipment used in high-risk and high-hazard areas must not exceed e.g. 12 V AC and 30 V DC.

IEC 60038 has set the nominal voltages of 230/400, 400/690 and 1000V for low voltage three-phase and four-wire electrical systems. For single-phase three-wire electrical systems, the nominal voltage is set to 120/240V. The phase conductors used in these electrical systems are hazardous-live-parts which can cause death by touching.

For example, in Figure 1, the phase conductors L1, L2, L3, represent hazardous-live-parts.

Electrical installation of a multi-family residential building corresponding to the tn-c-s-type of system earthing

References

  1. IEC 60050-195-2021
  2. IEC 60950-1:2005+AMD1:2009+AMD2:2013 CSV
  3. IEC 60038:2009+AMD1:2021 CSV