That part of the earth fault loop impedance which is external to the circuit under consideration. For the supply cable it will be the impedance external to the installation. For other circuits, it is the sum of the impedance of the circuits on the supply side of the circuit under consideration and the impedance external […]
Z2 – That part of the earth fault loop impedance which comprises the impedance under earth fault conditions of the circuit protective conductor (cpc) of the circuit under consideration.
Z1 – That part of the earth fault loop impedance which comprises the impedance under earth fault conditions of the line conductor of the circuit under consideration.
Uninterruptible power supply (UPS)
An uninterruptible power supply (UPS) is used to maintain the supply to an essential service duringmains supply outages. On loss ofmains supply,a storage device in the UPS (battery) continues to power the connected load.
Nominal line voltage to earth (Uo)
Uo Nominal line voltage to earth. Assumed to be 230 V for grid connected systems.
A system having one point of the source of energy directly earthed, the exposedconductive-parts of the installation being connected to earth electrodes electrically independent of the earth electrodes of the source.
A system having one or more points of the source of energy directly earthed, the exposedconductive-parts of the installation being connected to that point by protective conductors.
Subject to Simultaneous Overload
Where circuits are grouped, there are two availablemethods of calculating the rating factor Cg to be applied: [BS7671:2018,Appendix 4,5.1.2:Equation 2] [BS7671:2018,Appendix 4,5.1.2:Equation 3,4]
Soil Thermal Resistivity
Relates to the ability of the soil, in which the cable is installed, to conduct heat energy away from the cable. The rating factor Cs is applied in cable sizing calculations to account for different soil thermal resistivities. For cables with Installation Methods 70 to 73, the values of Cs are found in BS7671:2018, Table4B3. […]
Residual Current Device (RCD)
AResidual Current Device (RCD) is amechanical switching device or association of devices intended to cause the opening of the contacts when the residual current* attains a given value under specified conditions. *Residual Current is the algebraic sum of the currents in the live conductors of a circuit at apoint in the electrical installation.