Question 1 of 15
What NEC Article provides guidelines for sizing overload protection for 3-phase motors?
NEC Article 430, Part III covers the requirements for motor overload protection.
Question 2 of 15
What is the primary function of motor overload protection?
Overload protection prevents damage from prolonged overload conditions.
Question 3 of 15
For motors with a service factor of 1.15 or greater, what percentage of the full-load current (FLC) is used to size the overload protection?
The NEC specifies 125% of FLC for motors with a service factor of 1.15 or higher.
Question 4 of 15
For motors with a marked temperature rise of 40°C or less, what percentage of the full-load current (FLC) is used to size the overload protection?
The NEC specifies 125% of FLC for motors with a temperature rise of 40°C or less.
Question 5 of 15
For motors with a service factor below 1.15 or temperature rise above 40°C, what percentage of the full-load current (FLC) is used to size the overload protection?
The NEC specifies 115% of FLC for these types of motors.
Question 6 of 15
Which of the following can be used as an overload protection device for a motor?
Fuses, circuit breakers, and thermal overload relays are all acceptable forms of overload protection.
Question 7 of 15
What is the service factor (SF) of a motor?
Service factor indicates how much the motor capacity can be exceeded for a short time.
Question 8 of 15
What does a motor nameplate temperature rise of 40°C signify?
The temperature rise indicates the temperature difference above ambient.
Question 9 of 15
If a motor operates 10°C above its rated temperature, approximately what is the reduction in the lifespan of its winding insulation?
Studies show that a 10°C increase in operating temperature can reduce insulation lifespan by 50%.
Question 10 of 15
According to NEC, where are fuses installed for motor overload protection?
Fuses are installed on all ungrounded conductors, and on the grounded conductor when applicable, according to NEC.
Question 11 of 15
A single-phase AC motor may require how many fuses for overload protection?
Depending on the supply system, it may need one or two fuses.
Question 12 of 15
A three-phase motor requires how many fuses for overload protection?
A three-phase motor requires three fuses, one in each line.
Question 13 of 15
Overload protection devices protect against which type of fault?
Overload devices are designed for overload protection only.
Question 14 of 15
According to NEC 430.6(A)(2), what value is used to determine the setting for separate motor overload protection?
The motor nameplate current rating is used to determine the overload protection setting.
Question 15 of 15
What is a common reason why overload protection settings might be allowed to be higher than the calculated value based on the full-load current?
Motors draw a higher current during startup, which can trigger overload devices if they are set too low.
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