AS IEC 60990:2018 pdf download.Methods of measurement of touch current and protective conductor current.
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 14) 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 I % 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 earth ing conductor, of the supply.
5.3 Configuration
The EQUIPMENT under test (EUT) shall be fully assembled and ready for use in the maximum configuration; it shall be connected to external signal voltages where applicable, as specified by the manufacturer for a single EQUIPMENT.
EQUIPMENT which is designed for multiple power sources, only one of which is required at a time (for example, for backup), shall be tested with only one source connected.
EQUIPMENT requiring power simultaneously from two or more power sources shall be tested with all power sources connected but with not more than one connection to protective earth.
5.4 Power connections during test
5.4.1 General
NOTE Examples of power distribution systems are given in Annex I.
EQUIPMENT shall be connected in a test configuration as shown Ifl 1-igure 6 to 1-igure 14, according to 5.4.2, 5.4.3 or 5.4.4, as appropriate.
EQUIPMENT committees should consider the possible need for the manufacturer to identify the power distribution system (TN, TT, IT) to which an EQUIPMENT is intended to be connected in its final application.
If the EUT is specified by the manufacturer for use only on certain power distribution systems, the EUT shall be tested only when connected to those systems.
EQUIPMENT to be connected only to TN or TT systems shall comply with 5.4.2. EQUIPMENT to be connected to IT systems shall comply with 5.4.3 and may also be connected to TN or TT systems.
Traditionally, TOUCH CURRENT was at its maximum at the highest supply voltage. Modern electronic power supplies will not always provide maximum TOUCH CURRENT under this supply condition. TOUCH CURRRENT may be maximized at the lowest voltage, i.e. maximum current draw, or under some other condition. Electric shock protection shall be provided under the worst case operating condition.
EQUIPMENT rated for a single voltage shall be tested at its rated voltage plus an appropnate working tolerance to allow for supply variations.
EQUIPMENT rated for a nominal voltage range shall be tested at the extremes of the voltage range, plus an appropriate working tolerance to allow for supply variations. The working tolerance is determined by the EQUIPMENT committee or by the manufacturer if necessary (for example, 0 %, -10 %I+6 % or +10 %).
EQUIPMENT rated for different nominal voltages or voltage ranges, using a voltage selector, shall be set for the highest nominal voltage or voltage range and then treated as above. Where voltage selection involves more complex switching than a rearrangement of transformer windings, additional tests may be necessary to determine the worst case.
If it is inconvenient to test EQUIPMENT at the specified voltage, it is permitted to test it at any available voltage within the rating of the EQUIPMENT and then calculate the results.AS IEC 60990 pdf download.