AS IEC 60990:2018 pdf download – Methods of measurement of touch current and protective conductor current

03-03-2022 comment

AS IEC 60990:2018 pdf download – Methods of measurement of touch current and protective conductor current.
5.4.4 Equipment for use on single-phase centre-earthed power supply systems or on centre-earthed delta power supply systems Single-phase EQUIPMENT shall be connected to a supply having its centre tap earthed (see Figure 7 and Figure 1 4). Three-phase EQUIPMENT shall be connected to the appropriate delta supply (see Figure 1 4). 5.5 Supply voltage and frequency 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. 5.5.2 Supply frequency Supply frequency shall be the maximum rated nominal frequency, or alternatively, measurements may be corrected by calculation for estimation of the worst case current. 6 Test procedure 6.1 General 6.1 .1 Touch current measurements Product committees may wish to exclude measurement of TOUCH CURRENT at some accessible parts, based upon the principle of limitation of voltage (see IEC 60364-4-41 ). If so, measurements shall be made for accessible voltage and then, if required, for weighted or unweighted TOUCH CURRENT according to Clause 6. Concern for ELECTRIC BURN effects may arise with d.c. or at high frequencies (for example, above 30 kHz for 3,5 mA TOUCH CURRENT ). At lower frequencies, startle-reaction and letgo- immobilization will be the dominant considerations. Where there is such a concern, the unweighted r.m.s. value of TOUCH CURRENT shall be measured (Figure 3), in addition to measurement for either startle-reaction (Figure 4), or inability to let go (Figure 5).
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.

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