Technical Measurements Flashcards

A rooftop unit is rated at 5 tons of cooling. What is its capacity in BTU per hour?

Answer: 60,000 BTU/h

One ton of refrigeration equals 12,000 BTU/h, so 5 tons equals 60,000 BTU/h.

A 120-volt circuit feeds a resistive heater with 10 ohms of resistance. How much current does it draw?

Answer: 12 amps

By Ohm's law, I = V/R = 120/10 = 12 amps.

What is the power consumed by a 240-volt single-phase resistive load drawing 20 amps?

Answer: 4,800 watts

For a resistive single-phase load, P = V × I = 240 × 20 = 4,800 W.

Which formula correctly calculates real power for a balanced three-phase load?

Answer: P = V × I × 1.732 × PF

Three-phase real power uses line voltage times line current times the square root of 3 (1.732) times power factor.

A 2-kilowatt exhaust fan runs for 5 hours. How much energy does it use?

Answer: 10 kWh

Energy equals power times time: 2 kW × 5 h = 10 kWh.

Which instrument is used to test the insulation resistance of motor windings?

Answer: Megohmmeter

A megohmmeter (megger) applies high DC voltage to measure insulation resistance in megohms.

What is the main advantage of a clamp-on ammeter for troubleshooting?

Answer: It measures current without breaking the circuit

A clamp meter senses the magnetic field around a conductor, so the circuit stays intact.