Question 1
When sizing conductors for a branch circuit, which factor is MOST important to ensure the conductor does not overheat in normal operation?
Question 2
In a motor starter, what is the primary function of the overload relay compared to the short-circuit protective device?
Question 3
A three-phase 600 V motor has a nameplate full-load current of 28 A. The code table full-load current for this size is 32 A. Which value is normally used to size the branch-circuit short-circuit and ground-fault protection?
Question 4
A 120 V branch circuit with a 15 A breaker supplies general lighting. The connected load is 10 A. What is the approximate load percentage of the breaker rating?
Question 5
A 20 A branch circuit supplies a continuous load. What is the maximum continuous load that should normally be connected, according to common code practice?
Question 6
A 120 V, 20 A branch circuit supplies four identical 600 W portable heaters. Approximately what current will the circuit carry at full load?
Question 7
When sizing an overcurrent device for a single-phase motor, which general guideline is commonly applied to the motor full-load current for short-circuit and ground-fault protection?
Question 8
Calculate the synchronous speed of a 4-pole AC motor operating at 60 Hz.
Question 9
A 3-phase, 4-pole induction motor is connected to a 600V, 60Hz supply. The rotor is spinning at 1750 RPM. What is the percent slip?
Question 10
Calculate the synchronous speed of a 6-pole induction motor operating at 60 Hz.
Question 11
Calculate slip if sync speed is 1800 RPM and rotor speed is 1750 RPM.
Question 12
An electrician is sizing a 3-phase, 600V feeder for a 50 HP induction motor with a nameplate FLA of 52A. If the terminals are rated at 75°C and the conductors are copper, what is the minimum required ampacity for the feeder conductors according to general motor circuit rules?
Question 13
What is the 'Full Load Current' of a 10 HP, 208V, 3-phase motor, using standard industry reference tables (approximate)?
Question 14
According to motor circuit rules, what is the minimum required ampacity for branch circuit conductors supplying a single continuous-duty 10 HP, 600V, 3-phase motor with a nameplate FLA of 11A?
Question 15
An electrician is sizing a 3-phase, 600V feeder for a single 50 HP induction motor with a nameplate FLA of 52A. Using standard CEC motor circuit concepts, what is the minimum required ampacity for the branch circuit conductors?
Question 16
An electrician is sizing the branch circuit conductors for a single 10 HP, 208V, 3-phase induction motor with a nameplate FLA of 30.8 A. What is the minimum required ampacity for the conductors?
Question 17
An electrician is sizing the branch circuit for a single 120V, 1 HP motor with a nameplate current of 16A. What is the minimum standard ampacity required for the conductors?
Question 18
A 240 V, single-phase motor is rated at 10 A full-load current. Approximately what size of branch-circuit overcurrent device might be selected before considering any specific code tables or manufacturer data?
Question 19
A 30 kW, 600 V, three-phase motor has a full-load current of approximately 34 A. The design calls for a 125% sizing of conductors for the motor circuit. What approximate current should the conductor ampacity be based on?
Question 20
A facility experiences frequent nuisance tripping of a 30 A breaker feeding a non-motor load operating at about 28 A continuously. What is the MOST appropriate corrective action?
Question 21
A 120 volt, 15 ampere general-purpose branch circuit in a dwelling is supplying 1.44 kilowatts of load. What is the approximate load current?
Question 22
A motor nameplate lists full-load current of 9 amperes at 240 volts. The branch circuit conductors are sized for 125 percent of full-load current. What is the minimum conductor ampacity required?
Question 23
When sizing branch-circuit conductors and short-circuit protection for a single motor, which current value should generally be used as the basis?
Question 24
A 120 V, 20 A branch circuit in a shop supplies three receptacle loads operating simultaneously: 6 A, 4 A, and 5 A. Is the circuit within its rating, and what is the total load in watts?
Question 25
A feeder supplies three motors: one 10 HP, one 7.5 HP, and one 5 HP, all 480 V three-phase. When sizing the feeder overcurrent protection using typical code rules, how are these motor loads generally combined?
Question 26
A continuous load is one expected to run for at least how many hours at its maximum current?
Question 27
A 240 V single-phase motor is nameplated at 10 A full-load current. If using Ohm's law, what is the approximate running impedance of the motor at full load?
Question 28
A motor nameplate lists a full-load current (FLA) value. How should this value generally be used by an electrician?
Question 29
A motor nameplate shows 10 FLA at 240 V, single-phase. Approximately what current would you expect if the same motor is loaded to 50% of its rated mechanical load?
Question 30
A 240 V electric water heater is rated at 4500 W. What is the minimum branch circuit current used for sizing, assuming the load is considered continuous at 125% of nameplate amperes?