Electrical Systems & Wiring Flashcards

What is the function of a variable frequency drive (VFD) in a motor circuit?

Answer: To control motor speed by varying the frequency and voltage supplied to the motor

A VFD adjusts the output frequency and voltage to control motor speed, enabling energy savings and process control.

What does 'power factor' represent in an AC electrical system?

Answer: The ratio of real power to apparent power in an AC circuit

Power factor (PF = kW/kVA) indicates how effectively current is being used; a PF of 1.0 means all current does useful work.

Which type of hazardous area classification applies to locations where flammable gases are present under normal operating conditions?

Answer: Class I, Division 1

Class I, Division 1 locations have ignitable concentrations of flammable gases present continuously or intermittently under normal conditions.

In a 480V three-phase system, what is the approximate line-to-neutral voltage?

Answer: 277 V

Line-to-neutral voltage equals line-to-line voltage divided by √3; 480 ÷ 1.732 ≈ 277 V.

A fuse blows repeatedly in a motor circuit. Before replacing the fuse with a larger one, what should the technician do first?

Answer: Investigate the root cause such as a motor fault, overload, or short circuit

Replacing a fuse with a larger size without identifying the root cause can lead to equipment damage or fire.

What is 'wire gauge' and how does it relate to current-carrying capacity?

Answer: Wire gauge measures conductor diameter using AWG; smaller gauge numbers indicate larger wire with higher ampacity

In the AWG system, a lower number (e.g., 4 AWG) means a larger-diameter conductor capable of carrying more current than a higher number (e.g., 12 AWG).

What happens to motor torque when supply voltage is reduced by 10%?

Answer: Torque decreases by approximately 19% because torque is proportional to voltage squared

Motor torque is proportional to the square of the applied voltage, so a 10% voltage reduction causes roughly a 19% torque drop.