- B Table Q1 B Tabulates The Load For A Medium Size Industry In Parit Raja The Loads Are Balanced Over The Three Phase 1 (27.23 KiB) Viewed 48 times
\begin{tabular}{|l|l|} \hline i & A single induction motor taking 20 kW and operate at 0.75 PF lagging \\ \hline ii & An electric pump taking 25kVA and operate at 0.92PF lagging \\ \hline iii & Lumped load rated at 8 kW and operating at unity PF \\ \hline iv & Lumped load rated at 15kVAr and operating at 0.68PF lagging \\ \hline \end{tabular}
(c) A single phase motor circuit is protected by a 63 A circuit breaker. A fault occurs and causes a current of 98 A to flow through the earth continuity path. Due to the poor contact of lock nut and bush connecting a steel conduit to a metal box, the resistance of this conduit connection alone is 0.5Ω. Regulation D22 regarding the basic earthing requirements is given in Table Q2(c). (i) Predict whether the protective device will be damaged. (ii) Estimate the amount of heat produced at the metal box. (iii) Suggest the degree of risk of a fire developing.
Regulation D22 (Basic Earthing Requirements) States that earth leakage protection may be provided by means of fuses or excess current circuit breakers if the earth fault current available to operate the protective device and so make the faulty circuit dead exceeds: 1. 3 times the current rating of any semi enclosed fuse or any cartridge fuse having a fusing factor exceeding 1.5, used to protect the circuit, or 2. 2.4 times the rating of any cartridge fuse having a fusing factor not exceeding 1.5, used to protect the circuit, or 3. 1.5 times the tripping current of any excess current circuit breaker used to protect the circuit.