Regular and accurate measurements are essential to ensure the smooth and continuous operation of an electrical installation. One of the measurements is loop impedance measurement. It is necessary to measure the loop impedance in order to obtain the compliance reports required for the electrical installation.
The loop impedance is measured between the protective earth (PE) and the power line (L). This measurement is also called welding impedance. If an electrical installation is protected by overcurrent protection elements, then it is necessary to measure the loop impedance. Current protection elements are used because of fault currents that occur when a short circuit occurs. In this case, the protection elements must open the circuit within the desired time interval. In order to do this, the impedance between the phase and the PEN conductor must be within the standards. All metal parts of the plant are combined with protection and neutral conductors and drawn as a common conductor throughout the network. This conductor is PEN conductor.
In order to measure the loop impedance, the measuring device takes a certain current from the phase line and transmits it to the ground via the ground line. This current flowing through the earth returns from the operating earth to the device, ie the phase conductor. In this direction, the sum of the resistance values of all the lines it passes through is called the loop impedance.
Within this sum, ie the impedance value, there are the following values: protection earth, operating earth, transformer secondary winding resistors, phase conductor resistance and protection earth conductor resistance. The sum of all these values gives the loop impedance.
If the measurement is carried out in this way, the measured ground value is correct. Because the protection elements will react to the short circuit current that will occur on this line. For example, if there is a short-circuit in the phase line of a machine body, the current path is five items.
The Importance of Making Cycle Impedance Measurement
If overcurrent arrangements are used for protection against indirect touch in systems with grounding type TN, it must be checked whether the selected conductor cross-sections correspond to the current required for each tripping time. For indirect contact protection, the loop impedance between the protection conductor and the main conductor and between the PEN conductor and the main conductor must be determined. Or, if the installation is protected by overcurrent protection elements, the fault loop impedance must be measured. In the event of a fault, the impedance between the PEN and the phase must be the smallest in order to open the circuit within a certain time interval. This value is only obtained by measurements with suitable measuring devices. Since there may be mains voltage oscillations at this time, it is necessary to take the average of several measurements. The loop impedance measurement must be performed at the furthest point of a current circuit.
In the Annex (III-III) of the Regulation on Health and Safety Conditions in the Use of Work Equipment issued by the Ministry of Labor and Social Security in 2013 (Annex-III), loop impedance measurement is included in the subject of installations. Accordingly, the conductors must have electrical impedance measurements, electrical engineers, electrical technicians or high technicians. Otherwise, the measurements will have no value.
The legal regulations that should be taken into consideration during the controls are explained as follows:
- Regulation on Grounding of Electrical Installations dated 2001
- Implementing Regulation on Electric High Current Installations dated 2000
- Electrical Indoor Facilities Regulation dated 1984
Many test and inspection organizations make loop impedance measurements. our organization TÜRCERT Technical Control and Certification Inc. provides cycle impedance measurement services with a competent manager and employee staff and a strong infrastructure.