What Is a Double Insulation? Definition, Meaning, Symbol, Requirements

Double insulation: an insulation comprising both basic insulation and supplementary insulation [defined in the IEC 60050-195-2021 and in the BS7671].

Double insulation is a protective measure in which:

  • basic protection is provided by basic insulation, and fault protection is provided by supplementary insulation, or
  • basic protection and fault protection are provided by reinforced insulation between hazardous-live-parts and accessible parts (accessible conductive parts and accessible surfaces of insulating material).

NOTE. This protective measure is intended to prevent the appearance of dangerous voltage on the accessible parts of electrical equipment through a fault in the basic insulation.

The protective measure by double insulation is applicable in all situations, unless some limitations are given in the corresponding Part 7 of IEC 60364.

Where this protective measure is to be used as the sole protective measure (i.e. where a whole installation or circuit is intended to consist entirely of equipment with double insulation or reinforced insulation), it shall be verified that effective measures, for example by adequate supervision, are in place so that no change can be made that would impair the effectiveness of the protective measure.

Therefore this protective measure shall not be applied to any circuit that includes, for example, a socket-outlet with an earthing contact, luminaire supporting coupler (LSC), device for connecting a luminaire (DCL) or cable coupler, or where a user may change items of equipment without authorization.

Requirements for Basic Protection and Fault Protection

Electrical Equipment

Where the protective measure, using double insulation, is used for the complete installation or part of the installation, electrical equipment shall comply with one of the following subclauses [2]:

  • 412.2.1.1 ; or
  • 412.2.1.2 and 412.2.2; or
  • 412.2.1.3 and 412.2.2.

Electrical equipment shall be of the following types, and type tested and marked to the relevant standards:

  • electrical equipment having double insulation (Class II equipment);
  • electrical equipment declared in the relevant product standard as equivalent to Class II, such as assemblies of electrical equipment having total insulation (see the IEC 61439 series).

NOTE. This equipment is identified by the symbol IEC 60417-5172: 2003-02 IEC 60417-5172:2003-02.

Electrical equipment having basic insulation only shall have supplementary insulation applied in the process of erecting the electrical installation, providing a degree of safety equivalent to electrical equipment according to 412.2.1.1 and complying with 412.2.2.1 to 412.2.2.3 [2].

The symbol IEC 60417-5019:2006-08 should be fixed in a visible position on the exterior and interior of the enclosure. See IEC 60417-5019:2006-08 and IEC 80416-3:2002, Clause 7.

Electrical equipment having uninsulated live parts shall have reinforced insulation applied in the process of erecting the electrical installation, providing a degree of safety equivalent to electrical equipment according to 412.2.1.1 and complying with 412.2.2.2 and 412.2.2.3 [2]; such insulation being recognized only where constructional features prevent the application of double insulation.

The symbol IEC 60417-5019:2006-08 should be fixed in a visible position on the exterior and interior of the enclosure. See IEC 60417-5019:2006-08 and IEC 80416-3:2002, Clause 7.

Enclosures

The electrical equipment being ready for operation, all conductive parts separated from live parts by basic insulation only, shall be contained in an insulating enclosure affording at least the degree of protection IPXXB or IP2X.

The following requirements apply as specified:

  • the insulating enclosure shall not be traversed by conductive parts likely to transmit a potential; and
  • the insulating enclosure shall not contain any screws or other fixing means of insulating material which might need to be removed, or are likely to be removed, during installation and maintenance and whose replacement by metallic screws or other fixing means could impair the enclosure’s insulation.

Where the insulating enclosure must be traversed by mechanical joints or connections (e.g. for operating handles of built-in apparatus), these should be arranged in such a way that protection against shock in case of a fault is not impaired.

Where lids or doors in the insulating enclosure can be opened without the use of a tool or key, all conductive parts which are accessible if the lid or door is open shall be behind an insulating barrier (providing a degree of protection not less than IPXXB or IP2X) preventing persons from coming unintentionally into contact with those conductive parts. This insulating barrier shall be removable only by use of a tool or key.

Conductive parts enclosed in the insulating enclosure shall not be connected to a protective conductor. However, provision may be made for connecting protective conductors which necessarily run through the enclosure in order to serve other items of electrical equipment whose supply circuit also runs through the enclosure. Inside the enclosure, any such conductors and their terminals shall be insulated as though they were live parts, and their terminals shall be marked as PE terminals.

Exposed-conductive-parts and intermediate parts shall not be connected to a protective conductor unless specific provision for this is made in the specifications for the equipment concerned.

The enclosure shall not adversely affect the operation of the equipment protected in this way.

Installation

The installation of equipment mentioned in 412.2.1 [2] (fixing, connection of conductors, etc.) shall be effected in such a way as not to impair the protection afforded in compliance with the equipment specification.

Except where 412.1.2 [2] applies, a circuit supplying items of Class II electrical equipment shall have a circuit protective conductor run to and terminated at each point in wiring and at each accessory.

NOTE. This requirement is intended to take account of the replacement by the user of Class II equipment by Class I electrical equipment.

Wiring Systems

Wiring systems installed in accordance with IEC 60364-5-52 are considered to meet the requirements of 412.2 [2] if they consist of:

  • conductors having insulation with a rated voltage not less than the nominal voltage of the system and at least 300 V/ to 500 V, enclosed in trunking or ducting with electrical insulating characteristics complying with the IEC 61084 series, or conduit with electrical insulating characteristics complying with the IEC 61386 series, or
  • cable adequate to withstand electric, thermal, mechanical and environmental stresses with the same reliability of protection as provided by double insulation.

NOTE 1. Such wiring systems are not identified by the symbol IEC 60417-5172: 2003-02 IEC 60417-5172:2003-02 or by the symbol IEC 60417-5019:2006-08 IEC 60417-5019:2006-08 and IEC 80416-3:2002, Clause 7.

NOTE 2. In Italy, wiring systems installed in accordance with IEC 60364-5-52 in electrical systems with nominal voltages not higher than 690 V, are considered to meet the requirements of 412.2 [2] if the following cables or insulated conductors are used:

  • cables, provided with a non-metallic sheath, having a rated voltage one step higher than the nominal voltage of the system; or
  • insulated conductors installed in insulating conduits or insulating trunkings complying with the relevant standards; or
  • cables, provided with a metallic sheath, having between the conductors and the metallic sheath and between such metallic sheath and the external surface, an insulation adequate for the nominal voltage of the electrical system.

References