Detail of GB/T 16895.21-2020

Introduction of GB/T 16895.21-2020

GB/T 16895 consists of 5 parts (each part is classified into several sub-parts) under the general title Low-voltage electrical installations: ——Part 1: Fundamental principles assessment of general characteristics definitions; ——Part 4: Safety protection; ——Part 5: Selection and erection of electrical equipment; ——Part 6: Verification; ——Part 7: Requirements for special installations or locations. This is Part 4-41 of GB/T 16895. This part is developed in accordance with the rules given in GB/T 1.1-2009. This part replaces GB/T 16895.21-2011 Low-voltage electrical installations—Part 4-41: Protection for safety—Protection against electric shock. The following main technical changes have been made with respect to GB/T 16895.21-2011: ——The terms given in GB/T 17045-2020 are adopted; ——The scope of protective equipotential bonding is modified (see 411.3.1.2 hereof; 411.3.1.2 of Edition 2011); ——The requirements for automatic disconnection of power supply are modified (see 411.3.2 hereof; 411.3.2 of Edition 2011); ——The requirements for setting RCD in domestic lighting circuit are added (see 411.3.4 hereof); ——The fault protective measures of IT system are modified (see 411.6 hereof; 411.6 of Edition 2011); ——The requirements for wiring are modified (see 412.2.4 hereof; 412.2.4 of Edition 2011); ——The Annex D "Protection provisions where automatic disconnection of power supply according to 411.3.2 is not feasible” are added. This part, by means of translation, is identical to IEC 60364-4-41: 2017 Low-voltage electrical installations—Part 4-41: Protection for safety—Protection against electric shock. The Chinese document consistent and corresponding with the normative international document in this part is as follows: ——GB/T 7251 (all parts) Low-voltage switchgear and controlgear assemblies [IEC 61439 (all parts)]; ——GB/T 16499-2017 Guide for the preparation of electrical and electronic safety publications and the use of basic safety publications and group safety publications (IEC Guide 104: 2010, NEQ); ——GB/T 16895.3-2017 Low-voltage electrical installations—Part 5-54: Selection and erection of electrical equipment—Earthing arrangements and protective conductors (IEC 60364-5-54: 2011, IDT); ——GB/T 16895.6-2014 Low-voltage electrical installations—Part 5-52: Selection and erection of electrical equipment—Wiring systems (IEC 60364-5-52: 2009, IDT); ——GB/T 16895.23-2012 Low-voltage electrical installations—Part 6: Verification (IEC 60364-6: 2006, IDT); ——GB/T 17045-2020 Protection against electric shock—Common aspects for installation and equipment (IEC 61140: 2016, IDT); ——GB/T 19212.7-2012 Safety of transformers, reactors, power supply units and similar products for supply voltages up to 1,100V—Part 7: Particular requirements and test for safety isolating transformers and power supply units incorporating safety isolating transformers (IEC 61558-2-6: 2009, IDT); ——GB/T 19215 (all parts) Cable trunking and ducting systems for electrical installations [IEC 61084 (all parts)]; ——GB/T 20041 (all parts) Conduit systems for electrical installations [IEC 61386 (all parts)]. Editorial changes have been made in this part as follows: The contents of international standard correction sheet IEC 60364-4-41: 2005 + AMD1: 2017 CSV/COR1: 2018 are included; ——The Annex E “List of notes concerning certain countries” is deleted. This standard was proposed by and is under the jurisdiction of the National Technical Committee for Electrical Installations Standardization of Buildings (SAC/TC 205). The previous editions of the part replaced by these following ones: ——GB 16895.21-2004 and GB/T 16895.21-2011.   410 Introduction This part of GB/T 16895 deals with protection against electric shock as applied to electrical installations. It is based on GB/T 17045-2020, which is a basic electrical safety standard for human and livestock. GB/T 17045-2020 is intended to specify the basic principles and requirements for electrical installations and equipment or their co-ordination. The basic principles of protection against electric shock, according to GB/T 17045-2020, is that hazardous-live-parts must not be accessible and accessible conductive parts must not be hazardous live, neither under normal conditions nor under single fault conditions. According to 4.2 of GB/T 17045-2020, the basic protection provisions shall be used under normal conditions and the fault protection provisions shall be used under single fault conditions. Alternatively, enhanced protection provisions can also be adopted for electric shock protection, which can provides protection under normal conditions and single fault conditions. This part is one of the compilations of safety publication for protection against electric shock. Low-voltage electrical installations— Part 4-41: Protection for safety—Protection against electric shock 410.1 Scope This part of GB/T 16895 specifies basic requirements for protection against electric shock, including basic protection (protection against direct contact) and fault protection (protection against indirect contact) of human and livestock. It also specifies the application and co-ordination of these requirements according to the conditions of external influence. This part also specifies the requirements for additional protection under specific circumstances. 410.2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60364-5-52 Low-voltage electrical installations—Part 5-52: Selection and erection of electrical equipment—Wiring systems IEC 60364-5-54 Low-voltage electrical installations—Part 5-54: Selection and erection of electrical equipment—Earthing arrangements and protective conductors IEC 60364-6 Low-voltage electrical installations—Part 6: Verification IEC 61084 (all parts) Cable trunking and ducting systems for electrical installations IEC 61140 Protection against electric shock—Common aspects for installation and equipment IEC 61386 (all parts) Conduit systems for electrical installations IEC 61439 (all parts) Low-voltage switchgear and controlgear assemblies IEC 61558-2-6 Safety of power transformers, power supply units and similar—Part 2-6: Particular requirements for safety isolating transformers for general use IEC 62477-1 Safety requirements for power electronic converter systems and equipment—Part 1: General IEC Guide 104 The preparation of safety publications and the use of basic safety publications and group safety publications   410.3 General requirements 410.3.1 In this part, the following specification of voltages is intended unless otherwise stated: ——a.c. voltages (r.m.s.); ——ripple-free d.c. voltages. Ripple-free is conventionally defined as an r.m.s. of ripple voltage of not more than 10% of the d.c. component. 410.3.2 Protective measure shall consist of: ——appropriate combination of basic protection provisions and independent fault protection provisions, or ——enhanced protection provision which provides both basic protection and fault protection. Additional protection is specified as part of a protective measure under certain conditions of external influence and in certain special locations (see the corresponding Part 7 of IEC 60364 series standards). Note 1: For special applications, protective measures which do not follow this concept are permitted (see 410.3.5 and 410.3.6). Note 2: The reinforced insulation is an example of enhanced protective measure. 410.3.3 In each part of electrical installation, one or more protective measures shall be applied, taking account of the conditions of external influence. The following protective measures generally are permitted: ——automatic disconnection of power supply (see Clause 411); ——double or reinforced insulation (see Clause 412); ——electrical separation for the supply of one item of current-using equipment (see Clause 413); ——extra-low voltage [safety extra-low voltage (SELV) and protective extra-low voltage (PELV)] (see Clause 414). The above protective measures applied in the installation shall be considered in the selection and erection of equipment. See 410.3.4 to 410.3.9 for the particular installations. Note: In electrical installations, the most commonly used protective measure is automatic disconnection of power supply. 410.3.4 For special installations or locations, the particular protective measures in the corresponding Part 7 of IEC 60364 shall be applied. 410.3.5 The protective measures, specified in Annex B, i.e. the use of obstacles and placing out of arm’s reach, shall only be used in installations accessible to the following personnel: ——skilled or instructed personnel, or ——personnel under the supervision of skilled or instructed personnel. 410.3.6 The protective measures specified in Annex C include: ——non-conducting location, ——earth-free local equipotential bonding, ——electrical separation for the supply of more than one item of current-using equipment, which may be applied only when the installation is under the supervision of skilled or instructed personnel, so that unauthorized changes cannot be made. 410.3.7 If certain requirements of a protective measure cannot be met, additional protection provisions shall be applied to achieve the same degree of safety effect. Note: See 411.7 for an example of the application of this provision. 410.3.8 Different protective measures applied to the same installation or part of an installation or within equipment shall have no influence on each other, such that failure of one protective measure could impair the other protective measures. 410.3.9 The fault protection provisions may be omitted for the following parts: ——metal supports of overhead line insulators which are attached to the building and are placed out of arm’s reach; ——steel reinforced concrete poles of overhead lines in which the steel reinforcement is not accessible; ——exposed-conductive-parts which, owing to their reduced dimensions (approximately 50 mm × 50 mm) or their disposition cannot be gripped or come into significant contact with a part of the human body and provided that connection with a protective conductor could only be made with difficulty or would be unreliable; Note: The above example applies to bolts, rivets, nameplates and cable clips. ——metal tubes for laying lines or other metal enclosures for protecting equipment in accordance with Clause 412. 411 Protective measure: automatic disconnection of power supply 411.1 General Automatic disconnection of power supply is a protective measure in which: ——basic protection is provided by basic insulation of live parts or by barriers or enclosures, in accordance with Annex A, and ——fault protection is provided by protective equipotential bonding and automatic disconnection of power supply in case of a fault in accordance with 411.3 to 411.6. Note 1: Where this protective measure is applied, Class II equipment may also be used. Where specified, additional protection is provided by a residual current protective device (RCD) with a rated residual operating current not exceeding 30 mA in accordance with 415.1. Note 2: Residual current monitors (RCMs) are not protective devices but they may be used to monitor residual currents in electrical installations. RCMs produce an audible or audible and visual signal when a preselected value of residual current is exceeded 411.2 Requirements for basic protection All electrical equipment shall comply with one of the basic protection provisions described in Annex A or, where appropriate, Annex B. 411.3 Requirements for fault protection 411.3.1 Protective earthing and protective equipotential bonding 411.3.1.1 Protective earthing Exposed-conductive-parts shall be connected to a protective conductor under the specific conditions for each type of system earthing as specified in 411.4 to 411.6. Simultaneously accessible exposed-conductive-parts shall be connected to the same earthing system individually, in groups or collectively. Conductors for protective earthing shall meet the requirements of IEC 60364-5-54. Each circuit shall have a protective conductor connected to the relevant earthing terminal. 411.3.1.2 Protective equipotential bonding The metallic parts of non-electrical installation that enter each building and easily introduce dangerous potential difference shall be connected to the main earthing terminal by protective equipotential bonding conductors; examples of such metallic parts may include: ——pipelines supplying services into the building, for example gas, water, district heating systems, etc.; ——structural extraneous-conductive-parts; ——accessible reinforcements of constructional reinforced concrete. Where such conductive parts introduced outside from the building, they shall be close enough to the entrance of building for equipotential bonding. Protective equipotential bonding is not required for the metallic pipes entering the building with insulating section installed at their entrance. Note: See 542.4.1 of IEC 60364-5-54:2011 for other connections with the main earthing terminal. 411.3.2 Automatic disconnection of power supply in case of fault 411.3.2.1 A protective device shall automatically switch off the supply to the line conductor of a circuit or equipment in case of fault of negligible impedance between the line conductor and an exposed-conductive-part or a protective conductor of the circuit or equipment within the disconnection time required in 411.3.2.2, 411.3.2.3 or 411.3.2.4. The device shall at least be suitable for isolation of the line conductors. Note: For IT systems, automatic disconnection of power supply is not usually required on the occurrence of a first fault (see 411.6.1). See 411.6.3.2 for the requirements for automatic disconnection of power supply in case of second fault of different live conductors 411.3.2.2 For terminal circuits not exceeding the following rated current, the maximum disconnection time shall meet those specified in Table 41.1: ——63A for circuit with one or more socket-outlets; and ——32A for circuit supplying power only to fixed connected current-using equipment. Table 41.1 Maximum disconnection time System 50V < U0 ≤ 120V s 120V < U0 ≤ 230V s 230V < U0 ≤ 400V s U0 > 400V s Voltage a.c. d.c. a.c. d.c. a.c. d.c. a.c. d.c. TN 0.8 a 0.4 1 0.2 0.4 0.1 0.1 TT 0.3 a 0.2 0.4 0.07 0.2 0.04 0.1 Where in TT system the disconnection is achieved by an overcurrent protective device and the protective equipotential bonding is connected with all extraneous-conductive-parts within the installation, the maximum disconnection time applicable to TN system specified in the table may be used. U0: the nominal voltage of a.c. or d.c. line to earth. Note: See Note 4 of 411.4.4, 411.5.3 and Note 4 of 411.6.4 b) for the requirements for disconnection time provided by residual current protective device (RCD). a Disconnection of power supply may be for reasons other than protection against electric shock. 411.3.2.3 In TN systems, the disconnection time for distribution circuits and circuits not covered by 411.3.2.2 shall not exceed 5s. 411.3.2.4 In TT systems, the disconnection time for distribution circuits and circuits not covered by 411.3.2.2 shall not exceed 1s. 411.3.2.5 Where it is not feasible for an overcurrent protective device to disconnect the supply in accordance with 411.3.2 or the use of a residual current protective device (RCD) for this purpose is not appropriate, see the protection provisions in Annex D. However, disconnection of power supply may be for reasons other than protection against electric shock. 411.3.2.6 If automatic disconnection of power supply according to 411.3.2.1 cannot be achieved in the time required by 411.3.2.2, 411.3.2.3, or 411.3.2.4, supplementary protective equipotential bonding measures shall be provided in accordance with 415.2. 411.3.3 Requirements for socket-outlets and for the supply of mobile equipment for use outdoors Additional protection by means of the residual current protective device (RCD) with a rated residual operating current not exceeding 30 mA shall be applied for: ——a.c. socket-outlets with a rated current not exceeding 32A that are for liable to be used by ordinary personnel and are intended for general use, and ——a.c. mobile equipment for use outdoors with rated current rating not exceeding 32A This subclause does not apply for IT systems in which the fault current, in case of a first fault, does not exceed 15 mA. Note: Additional protection in d.c. systems is under consideration. 411.3.4 Additional requirements for circuits with luminaires in TN and TT systems For a.c. terminal circuits supplying luminaires to single household, the residual current protective device (RCD) with a rated residual operating current not exceeding 30 mA shall be provided. 411.4 TN system 411.4.1 In TN systems, the integrity of the earthing of the electrical installation depends on the reliable and effective connection of the PEN or PE conductors to earth. Where the earthing is provided from a public or other supply system, compliance with the conditions external to the electrical installation is the responsibility of the supply network operator. Note: Examples of above conditions are as follows: ——the PEN conductor is connected to earth at multiple points and is installed in such a way as to minimize the risk of arising from a break in the PEN conductor; ——R_B/R_E ≤50/(U_0-50). where, RB——the earth electrode resistance of all earth electrodes in parallel, Ω; RE——the minimum contact resistance with earth of extraneous-conductive-parts not connected to a protective conductor, through which a fault between line and earth may occur, Ω; U0——the nominal a.c. r.m.s. voltage to earth, V. 411.4.2 The neutral point or the midpoint of the power supply system shall be earthed. If a neutral point or midpoint is not available or not accessible, a line conductor shall be earthed. Exposed-conductive-parts of the electrical installation shall be connected by a protective conductor to the main earthing terminal of the installation which shall be connected to the earthed point of the power supply system. If other effective earth connections exist, the protective conductors should also be connected to the earthed points wherever possible. Additional earthed points, distributed as evenly as possible, can make the potentials of protective conductors remain, in case of a fault, as near as possible to that of earth. The protective conductors (PE and PEN) should be earthed where they enter any buildings, taking account of any diverted neutral currents of multiple earthed PEN conductors. 411.4.3 In fixed electrical installations, a single conductor may serve both as a protective conductor and a neutral conductor (PEN conductor) provided that the requirements of 543.4 of IEC 60364-5-54 are met. No switching or isolating device shall be inserted in the PEN conductor. 411.4.4 The characteristics of the protective devices (see 411.4.5) and the circuit impedances shall meet Equation (1): ZS × Ia ≤ U0 (1) where, ZS——the impedance of the fault circuit, Ω, comprising ● the power supply; ● the line conductor to the point of the fault; and ● the protective conductor between the point of the fault and the power supply; Ia——the current causing the automatic operation of the disconnecting device within the time specified in 411.3.2.2 or 411.3.2.3, A. When a residual current protective device (RCD) is used, this current is the residual operating current providing disconnection in the time specified in 411.3.2.2, or 411.3.2.3. U0——the nominal voltage of a.c. or d.c. line to earth, V. Note: In TN systems, the residual fault currents are significantly higher than 5IΔn. Therefore, the installation and the disconnection time of current protective devices (including selective and time delayed types) shall meet the requirements of IEC 61008-1, IEC 61009-1 or IEC 62423 and Table 41.1, respectively. When circuit-breakers providing residual current protection (CBRs) and the residual current monitoring module (MRCDs) that can be used in combination with the circuit breaker in accordance with IEC 60947-2 are used, adjusting of time delay shall meet those specified Table 41.1. 411.4.5 In TN systems, the following protective devices may be used for fault protection (protection against indirect contact): ——overcurrent protective devices; ——residual current protective devices (RCDs). Note 1: Where an RCD is used for fault protection, the circuit should also be protected by an overcurrent protective device in accordance with IEC 60364-4-43. A residual current protective device (RCD) shall not be used in TN-C systems. Note 2: If discrimination is required between RCDs, see 535.3 of IEC 60364-5-53: 2001. 411.5 TT systems 411.5.1 All exposed-conductive-parts collectively protected by the same protective device shall be connected by the protective conductors to an earth electrode common to all those parts. Where several protective devices are utilized in series, this requirement applies separately to all the exposed-conductive-parts protected by each device. The neutral point or the mid-point of the power supply system shall be earthed. If a neutral point or mid-point is not available or not accessible, a line conductor shall be earthed. 411.5.2 Generally in TT systems, RCDs shall be used for fault protection. Alternatively, overcurrent protective devices may be used for fault protection provided a suitably low value of Zs (see 411.5.4) is permanently and reliably assured. Note 1: Where an RCD is used for fault protection, the circuit should also be protected by an overcurrent protective device in accordance with IEC 60364-4-43. Note 2: The use of fault-voltage operated protective devices is not covered by this part. 411.5.3 Where a residual current protective device (RCD) is used for fault protection, the following conditions shall be met: 1) the disconnection time meets the requirements of 411.3.2.2 or 411.3.2.4; and 2) RA × IΔn ≤ 50V. where, RA——the sum of the resistance of the earth electrode and the protective conductor for the exposed conductive-parts, Ω; IΔn——the rated residual operating current of the RCD, mA. Note 1: Fault protection is provided in this case also if the fault impedance is not negligible. Note 2: If discrimination is required between RCDs, see 535.3 of IEC 60364-5-53: 2001. Note 3: Where RA is not known, it may be replaced by ZS. Note 4: The disconnection times in accordance with Table 41.1 relate to prospective residual fault currents significantly higher than the rated residual operating current IΔn of the RCD (typically 5IΔn). 411.5.4 Where an overcurrent protective device is used, Equation (2) shall be met: ZS × Ia ≤ U0 (2) where, ZS——the impedance of the fault circuit, Ω, comprising ● the power supply; ● the line conductor to the point of the fault; ● the protective conductor of the exposed-conductive-parts; ● the earthing conductor; ● the earth electrode of the electrical installation; and ● the earth electrode of the power supply. Ia——the current causing the automatic operation of the disconnecting device within the time specified in 411.3.2.2 or 411.3.2.4, A. U0——the nominal voltage of a.c. or d.c. line to earth, V. 411.6 IT system 411.6.1 In IT systems, the live parts shall be insulated from earth or connected to earth through sufficiently high impedance. This earthed point may be made either at the neutral point or midpoint of the system or at an artificial neutral point. The latter may be connected directly to earth if the resulting impedance to earth is sufficiently high at the system frequency. Where no neutral point or mid-point exists, a line conductor may be connected to earth through high impedance. The fault current is then low in the event of a single fault to an exposed-conductive-part or to earth and automatic disconnection of power supply in accordance with 411.3.2 is not imperative provided the condition in 411.6.2 is met. Protection provisions shall be taken, however, to avoid risk of harmful pathophysiological effects on a human body in contact with simultaneously accessible exposed-conductive-parts in the event of two faults existing simultaneously. Note: To reduce overvoltage or to damp voltage oscillation, it may be necessary to provide earthing through impedances or artificial neutral points, and the characteristics of these should be appropriate to the specific requirements of the installation. 411.6.2 Exposed-conductive-parts shall be earthed individually, in groups, or collectively. Equation (3) shall be met: In a.c. systems, the following condition shall be met to limit the touch voltage to: RA × Id ≤ 50V (3) where, RA——the sum of the resistance of the earth electrode and protective conductor for the exposed-conductive-parts, Ω; Id——the fault current of the first fault of negligible impedance between a line conductor and an exposed-conductive-part, A; Id takes account of leakage currents and the total earthing impedance of the electrical installation. Note: No touch voltage limitation is considered in d.c. systems as the Id can be considered to be negligibly low. 411.6.3 In IT systems, the following monitoring devices and protective devices may be used: ——insulation monitoring devices (IMDs); ——residual current monitoring devices (RCMs) ——insulation fault location systems (IFLS); ——overcurrent protective devices; ——residual current protective devices (RCDs). Note 1: Where RCD is used for protection, misoperation of the RCD in case of a first fault cannot be excluded due to capacitive leakage currents. Note 2: In case of faults in two different item of class I current-using equipment supplied by different line conductors, the protection operation of two fault circuit is only likely to be achieved if every single item of current-using equipment is protected by an individual RCD. The use of overcurrent protective devices is also suitable. 411.6.3.1 Where an IT system is designed not to disconnect the power supply in case of first fault, one of the following monitoring measures shall be taken: ——an insulation monitoring device (IMD), which may be combined with an insulation fault location system (IFLS), or ——a residual current monitor (RCM), provided that the residual current is sufficiently high to be detected. Note: RCMs are not able to detect symmetrical insulation faults. This monitor shall produce an audible and/or visual signal which shall continue as long as the fault persists. The signal can be initiated via a relay contact output, an electronic switching output or a communication protocol. A visual and/or an audible alarm system shall be arranged at a suitable place, so that it is perceived by responsible personnel. If there are both audible and visible signals, it is permissible for the audible signal to be cancelled. The first fault should be eliminated with the shortest practicable time. In addition, an insulation fault location system (IFLS) in accordance with IEC 61557-9 may be provided to indicate the location of a first fault from a live part to exposed-conductive-parts or earth or other reference point. 411.6.4 After the occurrence of a first fault, conditions for automatic disconnection of power supply in case of a second fault occurring on a different live conductor shall be as follows: a) Where exposed-conductive-parts are interconnected by a protective conductor collectively earthed to the same earthing system, the conditions similar to a TN system apply, ie. Equations (4) and (5) shall be met where the neutral conductor is not distributed in a.c. systems and d.c. systems: 2Ia × ZS ≤ U (4) where the neutral conductor or mid-point conductor is not distributed: 2Ia × ZS′ ≤ U0 (5)   where, U0——the nominal a.c. or d.c. voltage between line conductor and neutral conductor (or mid-point conductor), V; U——the nominal a.c. or d.c. voltage between line conductors, V; ZS——the impedance of the fault circuit comprising the line conductor and the protective conductor of the circuit, Ω; ZS′——the impedance of the fault circuit comprising the neutral conductor and the protective conductor of the circuit; Ω; Ia——the current causing operation of the protective device within the time required in 411.3.2.2 for TN systems or 411.3.2.3, A. Note 1: The time specified in Table 41.1 of 411.3.2.2 for the TN system is applicable to IT systems with a distributed or non-distributed neutral conductor or mid-point conductor. Note 2: The factor 2 in Equations (4) and (5) takes into account that in case of the simultaneous occurrence of two faults, the faults may exist in different circuits. Note 3: For the impedance of fault circuit, the most severe case should be taken into account, e.g., a fault on the line conductor at the power supply and simultaneously another fault on the neutral conductor of a current-using equipment of the circuit considered. b) Where the exposed-conductive-parts are earthed in groups or individually, Equation (6) shall be met: RA × Ia ≤ 50V (6) where, RA——the sum of the resistance of the earth electrode and protective conductor for the exposed-conductive-parts, Ω; Ia——the current causing automatic disconnection of the disconnection device in a time complying to that for TT systems in Table 41.1 of 411.3.2.2 or in a time complying to 411.3.2.4, A. Note 4: If compliance to the requirements of b) is provided by a residual current protective device (RCD) compliance with the disconnection times required for TT systems in Table 41.1 may require residual currents significantly higher than the rated residual operating current IΔn of the RCD applied (typically 5IΔn). 411.7 Functional extra-low voltage (FELV) 411.7.1 General Where, for functional reasons, a nominal voltage not exceeding 50V a.c. or 120V d.c. is used but all the requirements of Clause 414 relating to SELV or to PELV are not fulfilled, and where SELV or PELV is not necessary, the supplementary measures described in 411.7.2 and 411.7.3 shall be taken to ensure basic protection and fault protection. This combination of protection provisions is known as FELV. Note: Such conditions may, for example, be encountered when the circuit contains equipment (such as transformers, relays, remote-control switches, contactors) insufficiently insulated with respect to circuits at higher voltage. 411.7.2 Requirements for basic protection Basic protection shall be provided by either: ——basic insulation in accordance with Clause A.1 pf Annex A corresponding to the nominal voltage of the primary circuit of the power supply; ——barriers or enclosures in accordance with Clause A.2 of Annex A. 411.7.3 Requirements for fault protection The exposed-conductive-parts of the equipment of the FELV circuit shall be connected to the protective conductor of the primary circuit of the power supply, provided that the primary circuit is subject to protection by automatic disconnection of power supply described in 411.3 to 411.6. 411.7.4 Power supply The power supply of the FELV system shall be either a transformer with at least simple separation between windings or shall meet the requirements of 414.3. Note: If the system is supplied from a higher voltage system by equipment which does not provide at least simple separation between that system and the FELV system (such as autotransformers, potentiometers, semiconductor devices, etc.), the output circuit is deemed to be an extension of the input circuit and the FELV circuit should be protected by the protective measure applied on the input circuit.   411.7.5 Plugs and socket-outlets Plugs and socket-outlets for FELV systems shall meet the following requirements: ——plugs shall not be able to enter socket-outlets of other voltage systems; ——socket-outlets shall not admit plugs of other voltage systems; ——socket-outlets shall have contacts for protective conductors 412 Protective measure: double or reinforced insulation 412.1 General 412.1.1 When double or reinforced insulation is used as protective measures, the following requirements shall be met: ——basic protection is provided by basic insulation, and fault protection is provided by supplementary insulation; or ——basic and fault protection is provided by reinforced insulation between live parts and accessible parts. Note: This protective measure is intended to prevent the appearance of dangerous voltage on the accessible parts of electrical equipment due to basic insulation fault. The protective measure by double or reinforced insulation is applicable in all situations, unless some limitations are given in the corresponding Part 7 of IEC 60364 series standards. 412.1.2 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.   412.2 Requirements for basic protection and fault protection 412.2.1 Electrical equipment Where the protective measure, using double or reinforced insulation, is used for the complete installation or part of the installation, electrical equipment shall meet one of the following requirements: ——412.2.1.1; ——412.2.1.2 and 412.2.2; ——412.2.1.3 and 412.2.2. 412.2.1.1 Electrical equipment shall be of the following types, and its type test and mark shall meet relevant standards: ——electrical equipment having double or reinforced 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 IEC 61439 (all parts)]. Note: This equipment is identified by the symbol IEC 60417-5172: 2003-02. 412.2.1.2 Electrical equipment having basic insulation only shall have supplementary insulation applied in the process of erecting the electrical installation to make it have degree of safety equivalent to electrical equipment according to 412.2.1.1 and meet the requirements of insulation enclosure in 412.2.2.1 to 412.2.2.3. The symbol should be marked 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. 412.2.1.3 Electrical equipment having uninsulated live parts shall have reinforced insulation applied in the process of erecting the electrical installation, if it is not convenient to adopt double insulation due to equipment structure, to make it have degree of safety equivalent to electrical equipment according to 412.2.1.1 and meet the requirements of 412.2.2.2 and 412.2.2.3. Note: The symbol should be marked 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.

Contents of GB/T 16895.21-2020

Foreword i 410 Introduction iv 410.1 Scope 410.2 Normative references 410.3 General requirements 411 Protective measure: automatic disconnection of power supply 411.1 General 411.2 Requirements for basic protection 411.3 Requirements for fault protection 411.4 TN system 411.5 TT systems 411.6 IT system 411.7 Functional extra-low voltage (FELV) 412 Protective measure: double or reinforced insulation 412.1 General 412.2 Requirements for basic protection and fault protection 413 Protective measure: electrical separation 413.1 General 413.2 Requirements for basic protection 413.3 Requirements for fault protection 414 Protective measure: extra-low-voltage provided by SELV and PELV 414.1 General 414.2 Requirements for basic protection and fault protection 414.3 Power supplies for SELV and PELV 414.4 Requirements for SELV and PELV circuits 415 Additional protections 415.1 Additional protection: residual current protective devices (RCDs) 415.2 Additional protection: supplementary protective equipotential bonding Annex A (Normative) Provisions for basic protection Annex B (Normative) Protective measures of obstacles and placing out of arm's reach Annex C (Normative) Protective measures for application only when the electrical installations are controlled or supervised by skilled or instructed personnel Annex D (Normative) Protection provisions where automatic disconnection of power supply according to 411.3.2 is not feasible Bibliography