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...

  Breaker Size : Example: Design Current for the R-TPN Load of Max 10 KW value is 20.89 A We need to select the Next Higher size of Breaker available in the Market for Calculated Design Current (=20.89 A) Here In our Case 30/32 A breaker can be selected. It can be MCCB or MCB or RCBO depending upon requirements. Ib = 21 A In = 30 A Iz = 52.48 (From Cable Data) Note: The operating characteristics of a device protecting a conductor against overload shall satisfy the following two conditions: Ib <= In <= Iz I2 <= 1.45 Iz Ib = the current for which the circuit is designed, e.g. maximum demand In = the nominal current of the protective device Iz = the continuous current-carrying capacity of the conductor (see the AS/NZS 3008.1) I2 = the current ensuring the effective operation of the protective device and may be taken as equal to either— (a) the operating current in conventional time for circuit breakers (1.45 In); or (b) the fusing current in conventional time for fuses (1...

  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( )