13 A electric saw 2.8 kW to mains cable wound on drum extension reel Fig. 1 The diagram shows an extension reel used for power tools in a garage. The reel i...
Question 1 Report
The diagram shows an extension reel used for power tools in a garage. The reel is rated at 13 A and should be fully unwound before a high-power tool is used. A 2.8 kW electric saw is connected to the reel on a 230 V supply. The cable is still tightly wound around the plastic drum.
(a) What current is taken by the saw? [2]
(b) Which statement explains why the reel should be unwound: the cable becomes colder, the cable can lose heat, or the supply voltage becomes zero? [1]
(c) When the cable becomes too hot, what danger can result? [1]
(d) What is the maximum power that a 13 A reel can supply at 230 V? [1]
Answer Details
(a) \[I=\frac{P}{V}=\frac{2800\ \text{W}}{230\ \text{V}}=12.2\ \text{A}.\] [2]
(b) The reel should be unwound because the cable can lose heat. A tightly wound cable retains heat. [1]
(c) Overheating can melt the insulation, causing a fire or electric-shock hazard. [1]
(d) \[P=VI=230\ \text{V}\times13\ \text{A}=2990\ \text{W}\approx3.0\ \text{kW}.\] [1]
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