AS IEC 60990:2018 pdf free download – Methods of measurement of touch current and protective conductor current
5.5.1 Supply voltage
Supply voltage shall be measured at the EQUIPMENT supply terminals. 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 appropriate 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 %, -1 0 %/+6 % or +1 0 %). 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.
6.1 .2 Control switches, equipment and supply conditions
During TOUCH CURRENT measurements, the test environment, configuration, earthing and supply system shall be according to 5.3, 5.4 and 5.5. In order to maximize the current values during measurements, the configuration shall be varied by connection and disconnection of units that are part of the EQUIPMENT , as permitted by the manufacturer’s operating and installation instructions. Control switches e, g, l, n and p in Figure 6 to Figure 1 4 shall be manipulated as described in 6.2, while the conditions listed in this subclause and 6.2.1 are independently varied so as to give the maximum measured value or values. Product committees shall make an appropriate selection of these variables. Recent addition of ABNORMAL OPERATION as an operating condition in product standards as related to the electrical installation (e.g. the loss of PE or the inability to ensure polarity of supply) clarifies the test conditions under NORMAL operation and FAULT CONDITIONS to then be applied.
6.1 .3 Use of measuring networks
Appropriate measuring electrodes (see 5.2), measuring network (see 5.1 ) and measuring device (see G.4) shall be used in accordance with the appropriate systems of Figure 6 to Figure 1 4 (see 5.4) to make measurements of TOUCH CURRENT between simultaneously accessible parts, and between accessible parts and earth. The terminal A electrode shall be applied to each accessible part in turn. For each application of the terminal A electrode, the terminal B electrode shall be applied to earth, then applied to each of the other accessible parts in turn. For power systems with an earthed power conductor, the terminal B electrode may be connected directly to the earthed power conductor at the interface of the EUT and the power supply, instead of being connected to the protective conductor. This connection may be used even though the voltage difference between the protective conductor and the earthed power conductor is more than 1 % of the line-to-line voltage (see 4.2).