IEC 61557-3-2019 pdf download.Electrical safety in low voltage distribution systems up to 1 000 V a.c. and 1 500 V d.c. – Equipment for testing, measuring or monitoring of protective measures – Part 3: Loop impedance.
4 Requirements
4.1 General In addition to the requirements of IEC 61 557-1 :201 9, Clause 4, the requirements of Clause 4 of this document shall apply. Equipment intended to be used on the distribution system shall, at the minimum, be rated measurement category III according to IEC 61 01 0-2-030. Equipment intended to be used on socket outlets only can be rated for measurement category II according to IEC 61 01 0-2-030.
4.2 Measurement of loop impedance For measurements in close proximity to the transformer of the distribution system, equipment with a specified loop impedance measuring function (influence quantity for system phase angle at a minimum of 30°) shall be used or a specified additional operating uncertainty shall be taken into account by the user. In applications where the measurement of loop resistance is carried out in close proximity to the sourcing transformer (e.g. < 50 m) the system phase angle may be greater than 1 8° (e.g. up to 30°) and therefore the inductive part of the internal impedance of the transformer may not be negligible. When the loading by loading equipment causes transients on the distribution system, the operating uncertainty shall not be exceeded as a result of the transient. Equipment with specified influence quantity E 6.1 of system phase angle of approximately 1 8° shall be marked with the warning symbol according to IEC 61 01 0-1 :201 0, Table 1 , symbol 1 4, adjacent to the loop function marking or a warning shall be given on the display.
4.3 External resistance When external resistances are included in the calibration as a zero offset, this shall be indicated on the measuring instrument.
This offset shall remain included in the calibration as long as it is indicated on the measuring instrument regardless of any changes in range or function.
4.4 Fault voltage exceeding U L Fault voltages as a result of a measurement that exceed U L at the point of test shall be avoided. This can be achieved by automatic disconnection in accordance with IEC 61 01 0-1 :201 0/AMD1 :201 6, Figure 2.
4.5 Overvoltage The measuring equipment shall not be damaged nor shall the user be exposed to danger when the measuring equipment is connected to 1 20 % of the nominal voltage of the distribution system for which the measuring equipment has been designed. Protective devices of the test equipment shall not be activated. The user shall not be exposed to danger and the equipment shall not be damaged when the measuring equipment is accidentally connected to a voltage having a value of 1 73 % of its rated voltage to earth according to IEC 61 01 0-2-030 for 1 min. Protective devices of the test equipment can be activated. If the measuring equipment indicates the value of the voltage at its measuring terminals, it shall also indicate if the system voltage exists and if the live conductor is exchanged with the protective conductor.
5 Marking and operating instructions
5.1 Marking In addition to IEC 61 557-1 :201 9, 5.1 and 5.2, the following information shall be provided on the measuring equipment.
Marking is permitted on the display for any of the following:
– range of the resistance of the loop impedance or of the calculated short-circuit current respectively within which compliance with the uncertainty limits in accordance with 4.2 is maintained;
– nominal system voltage for which the equipment is rated;
– rated system frequency for which the equipment is rated;
– maximum system phase angle for which the equipment is designed when this angle is greater than 1 8°;
– rated voltage to earth and measurement category.IEC 61557-3 pf download.