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There are 12 tubular lamps of 60 watts on a street, each controlled by means of a switch. What should be the rating of the switch if the supply power is 225 volts and the power factor of the lamp is 0.8 assuming the safety factor to be 2?

There are 12 tubular lamps of 60 watts on a street, each controlled by means of a switch. What should be the rating of the switch if the supply power is 225 volts and the power factor of the lamp is 0.8 assuming the safety factor to be 2? Correct Answer 16 A

Concept:

Power is given by:

P = VI cosϕ 

where P = power

V = voltage

I = current 

cosϕ = power factor

SF = safety factor

Calculation:

Given, P = 60 Watts (power of one lamp)

Pnet = 12 × 60 = 720 Watts

V = 225 volts

cosϕ = 0.8

SF = 2

720 = (225 × I × 0.8)

720 = (225 × I × 0.8)

I = 4 A

Since,

We have,

SF = 2

Hence,

Rating of fuse = SF2 × I = (2)2 × 2 = 16 A

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