Calcuate Ze R1+R2 Zs
Please enter any two values to calculate the third
Note: the Ze values could be obtained direct enquiry from DNO or by direct measurement with multifunction tester. Its a good practice to measure R1+R2 & Zs.
Earth loop impedance values are measured while electrical inspection and testing to establish if the electrical installation is in good condition to put or stay in service. The measurements must comply with the permitted values of wiring regulations BS 7671.
What is Ze?
External loop impedance(Ze) is the prospective short-circuit current at the origin of the installation measured in ohms Ω. The value can be obtained by contacting the electrical distributor (DNO) or can be measured by using a multifunctional tester, it is not recommended to simply calculate the values.
Maximum permitted values for different earthing systems are:
- TT System: 21 Ω and add the resistance of the installed earth electrode.
- TN-S System: 0.8 Ω.
- TN-C-S System: 0.35 Ω.
What is R1+R2?
R1+R2 is a continuity test at the furthest point of the circuit measured in ohms Ω between line and earth conductors. It is required to use low resistance or multifunctional tester to obtain the values to record at the schedule of test results.
What is Zs?
Earth loop impedance (Zs) also known as Max Zs. The Zs could be calculated by using a multifunctional tester or it can be calculated by adding measured values to the formula below:
Zs=Ze+ (R1+R2)