You are an electrician on the job. The electrical blueprint shows that eight 500-W lamps are to be installed on the same circuit. The circuit voltage is 277V and is protected by a 20-A circuit breaker. A continuous-use circuit can be loaded to only 80% of its rating. Is a 20-A circuit large enough to carry this load

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Answer:

I = 14.44A

Explanation:

calculating 80% of the circuit breaker current

I = (80/100)20A = 16A

eight 500W lamps are to be installed on the circuit. assume they are connected in parallel

total power = 500 x 8 = 4000W

power = voltage x current

current = power/voltage = 4000W/277V = 14.4A

The current obtained is less than 80% of the circuit breaker.

20A circuit breaker is large enough to carry the load.

The watt is used to quantify the amount of power in a circuit

Yes the circuit is large enough to carry the load

The reason the above response is correct is as follows:

The given parameters are:

Number of 500-W lamp to be installed on the same circuit = 8

Circuit voltage, V = 227 V

Rating of circuit breaker on the circuit = 20-A

Allowable load for continuous use = 80% of the rating

Required:

To find the capacity of the circuit to carry the load

 

Solution:

The total power available in the circuit, [tex]P_{tot}[/tex] = 500-W × 8 = 4,000-W

Power, P = Voltage, V × Current, I

[tex]I = \dfrac{Power}{Voltage}[/tex]

The total current required in the circuit, [tex]I_{tot}[/tex], is therefore;

[tex]I_{tot} = \dfrac{P_{tot}}{V}[/tex]

[tex]I_{tot} = \dfrac{4,000\, W}{277 \, V} \approx 14.44 \, A[/tex]

The total current flowing in the circuit, [tex]I_{tot}[/tex] ≈ 14.44 A

The allowable continuous use current in the circuit, [tex]I_{allowabe}[/tex] = 80% of 20-A = 16-A

Therefore, the allowable current load of the circuit is more than the total current flowing in the circuit, [tex]I_{allowabe}[/tex] > [tex]I_{tot}[/tex] and the circuit is large enough to carry the load

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