AS IEC 60990 pdf download

AS IEC 60990 pdf download.Methods of measurement of touch current and protective conductor current
1 Scope
This International Standard defines measurement methods for – d.c. or a.c. current of sinusoidal or non-sinusoidal waveform, which could flow through the human body, and – current flowing through a protective conductor. The measuring methods recommended for TOUCH CURRENT are based upon the possible effects of current flowing through a human body. In this standard, measurements of current through networks representing the impedance of the human body are referred to as measurements of TOUCH CURRENT . These networks are not necessarily valid for the bodies of animals. The specification or implication of specific limit values is not within the scope of this standard. IEC TS 60479 series provides information regarding the effects of current passing through the human body from which limit values may be derived. This standard is applicable to all classes of EQUIPMENT , according to IEC 61 1 40. The methods of measurement in this standard are not intended to be used for – TOUCH CURRENTS having less than 1 s duration, – patient currents as defined in IEC 60601 -1 , – a.c. at frequencies below 1 5 Hz, and – currents above those chosen for ELECTRIC BURN limits. This basic safety publication is primarily intended for use by technical committees in the preparation of standards in accordance with the principles laid down in IEC Guide 1 04 and ISO/IEC Guide 51 . It is not intended for use by manufacturers or certification bodies independent of product standards. One of the responsibilities of a technical committee is, wherever applicable, to make use of basic safety publications in the preparation of its publications. The requirements, test methods or test conditions of this basic safety publication only apply when specifically referred to or included in the relevant publications.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply. 3.1 TOUCH CURRENT electric current through a human body or through an animal body when it touches one or more accessible parts of an installation or of EQUIPMENT [SOURCE: IEC 60050-1 95:1 998, 1 95-05-21 ] 3.2 PROTECTIVE CONDUCTOR CURRENT current which flows in a protective conductor 3.3 EQUIPMENT organized collection of electromechanical component parts and features to accomplish a defined task (as specified in the relevant product standard). Note 1 to entry: If not specified in the relevant standard, see Annex A. 3.4 GRIPPABLE PART part of the EQUIPMENT which could supply current through the human hand to cause muscular contraction around the part and an inability to let go Note 1 to entry: Parts which are intended to be gripped with the entire hand are assumed to be grippable without further investigation. 3.5 ELECTRIC BURN burning of the skin or of an organ, caused by passing an electric current across or through the surface [SOURCE: IEC 60050-604:1 987, 604-04-1 8]
4 Test site
4.1 Test site environment Test site environmental requirements shall be as specified in the EQUIPMENT standard. If limit values of less than 70 µA r.m.s. or 1 00 µA peak are specified, or if the EQUIPMENT contains large shields which may be driven by high-frequency signals, product committees shall refer to Annex B.4.2 Test transformer The use of a test transformer for isolation is optional. For maximum safety, a test transformer for isolation (T2 in Figure 2, T in Figure 6 to Figure 1 4) shall be used and the main protective earthing terminal of the EQUIPMENT under test (EUT) earthed. Any capacitive leakage in the transformer shall then be taken into account. As an alternative to earthing the EUT, the test transformer secondary and the EUT shall be left floating (not earthed), in which case the capacitive leakage in the test transformer need not be taken into account. If transformer T is not used, the EUT shall be mounted on an insulating stand and appropriate safety precautions taken, in view of the possibility of the body of the EUT being at hazardous voltage. 4.3 Earthed neutral conductor EQUIPMENT intended for connection to a TT or TN power distribution system shall be tested with minimum voltage between neutral and earth. NOTE Descriptions of various power distribution systems are given in Annex I. The protective conductor and the earthed neutral conductor for the EUT should have a voltage difference of less than 1 % of line-to-line voltage (see example in Figure 1 ). A local transformer, see 4.2, will achieve this requirement. Alternatively, if the voltage difference is 1 % or more, the following are examples of methods which, in some cases, will avoid measurement errors due to this voltage: – connecting the terminal B electrode of the measuring instrument network to the neutral terminal of the EUT instead of the protective earthing conductor (see 6.1 .2) of the supply; – connecting the earthing terminal of the EUT to the neutral conductor, instead of the protective earthing conductor, of the supply.