A small workshop is supplied with a 220 V single-phase mains
PHYSICS · Multi-part · CBSE · Physics · Magnetic Effects of Electric Current · Magnetic Effects of Electric Current
Problem
A small workshop is supplied with a 220 V single-phase mains. It uses the following appliances:
• Three fluorescent tube lights, each rated 40 W (used together for long durations)
• One drilling machine rated 800 W (may run simultaneously with the lights)
• One refrigerator rated 150 W whose starting current is four times its running current
The owner wants to install suitable protective devices in the wiring.
(i) Compute the running current drawn by each individual appliance.
(ii) Determine the maximum instantaneous current that may flow when all appliances operate together and the refrigerator is starting.
(iii) Select an appropriate current rating for the main fuse from 5 A, 10 A, 15 A and 20 A, giving clear justification.
(iv) State whether a separate fuse should be provided for the drilling machine and support your answer with one reason.
(v) Analyse the possible dangers if the metal body of the drilling machine is not earthed and a short circuit occurs inside it.