Innovating Electrical Engineering Calculations

411.5 TT system In this system, all exposed-conductive-parts and extraneous-conductive-parts of the installation must be connected to a common earth electrode. The neutral point of the supply system is normally earthed at a point outside the influence area of the installation earth electrode but need not be so. The impedance of the earth fault loop therefore consists mainly in the two earth electrodes (i.e., the source and installation electrodes) in series, so that the magnitude of the earth fault current is generally too small to operate overcurrent relays or fuses, and the use of a residual current operated device is essential. "BS 7671, 411.5.l Every exposed-conductive-part which is to be protected by a single protective device shall be connected, via the main earthing terminal, to a common earth electrode. However, if two or more protective devices are in series, the exposed-conductive-parts may be connected to separate earth electrodes corresponding to each protective d...

Earth fault loop impedance test : Earth fault loop impedance testing is performed to measure the impedance of the earth fault loop in an electrical circuit. The purpose of this test is to ensure that the electrical installation is safe and can operate properly under fault conditions. During the test, the circuit is energized and a test current is injected into the circuit. The voltage drop across the circuit is measured, and the impedance of the earth fault loop is calculated using Ohm's Law. If the earth fault loop impedance is too high, it may result in a high fault current, which can cause the protective device, such as a circuit breaker, to trip. If the impedance is too low, it may not allow enough current to flow to operate the protective device, which can result in a dangerous situation. During the test, the circuit may be tested with both trip and no-trip conditions. The trip condition involves the activation of the protective device, which is designed to disconnect the circ...

 Brief Calculation for earthing : Protective Conductor Sizes. Regulation 543.1.1: This can be achieved by either calculation (543.1.3) or selected (543.1.4) from Table 54.7. The formula used in 543.1.4 for calculating the size of a protective conductor is covered in great detail in a session inside our 17th edition BS7671. Selecting from Table 54.7 The protective conductor size is relative to the size of the line conductor which is represented by the letter 'S. Also, the far right column can usually be ignored as this is only used when the protective conductor and line conductor are of different materials.

  VBA ADDIN FOR ELECTRICAL CALCULATIONS Functions accessible in Excel : fx = CableTraySize( ) fx = CONTAINMENT( ) fx = EARTHING( ) fx = FAULTCURRENT( ) fx = kVA( ) fx = LLMF( ) fx = LMF( ) fx = LSF( ) fx = RSMF( ) fx = say( ) fx = TRCURRENT( ) fx = Z_CABLE( ) fx = Z_Transformer( ) fx = CABLE( ) fx = CURRENT( ) fx = MCCB( ) fx = SHORTCIR( ) fx = VDrop( )