NEC: Overcurrent Protection Device Sizing Quiz…

Q: What is the primary purpose of an overcurrent protection device (OCPD) in an electrical circuit?

To protect conductors and equipment from damage due to excessive current. — OCPDs prevent damage from overcurrents like short circuits & overloads.

Q: According to the NEC, which article covers overcurrent protection?

Article 240 — Article 240 is the NEC article dedicated to overcurrent protection.

Q: When sizing an OCPD for a continuous load, the OCPD must be rated at not less than what percentage of the continuous load current?

125% — NEC requires OCPDs to be sized at least 125% for continuous loads.

Q: For a non-continuous load, the OCPD must be sized to carry at least what percentage of the load current?

100% — For non-continuous loads, the OCPD must be rated at 100%.

Q: What is the primary factor that determines the ampacity of a conductor?

The material and size of the conductor, and ambient conditions — Ampacity depends on conductor type, size, and temperature effects.

Q: If a motor nameplate indicates a full-load current of 10 amps, and it's not a continuous duty motor, what is the minimum size OCPD permitted?

10 amps — For non-continuous loads, OCPD should be sized 100% of the load current.

Q: Where can you find the ampacity values for various conductors?

In the NEC tables (e.g., Table 310.15(B)(16) or equivalent). — NEC Tables provide ampacity based on conductor size and conditions.

Q: When sizing an OCPD for a motor, what must be considered in addition to the motor's full-load current?

The motor's starting current (locked-rotor current). — Starting currents are significantly higher than running currents for motors.

Q: What type of overcurrent protection is typically used for branch circuits?

Fuses and circuit breakers — Fuses and circuit breakers are the primary overcurrent protection.

Q: What is the purpose of the overcurrent protection device for a feeder circuit?

To protect the feeder conductors from overcurrent. — The OCPD protects the conductors carrying power to the connected loads.

Question 1 of 10

What is the primary purpose of an overcurrent protection device (OCPD) in an electrical circuit?

OCPDs prevent damage from overcurrents like short circuits & overloads.

Question 2 of 10

According to the NEC, which article covers overcurrent protection?

Article 240 is the NEC article dedicated to overcurrent protection.

Question 3 of 10

When sizing an OCPD for a continuous load, the OCPD must be rated at not less than what percentage of the continuous load current?

NEC requires OCPDs to be sized at least 125% for continuous loads.

Question 4 of 10

For a non-continuous load, the OCPD must be sized to carry at least what percentage of the load current?

For non-continuous loads, the OCPD must be rated at 100%.

Question 5 of 10

What is the primary factor that determines the ampacity of a conductor?

Ampacity depends on conductor type, size, and temperature effects.

Question 6 of 10

If a motor nameplate indicates a full-load current of 10 amps, and it's not a continuous duty motor, what is the minimum size OCPD permitted?

For non-continuous loads, OCPD should be sized 100% of the load current.

Question 7 of 10

Where can you find the ampacity values for various conductors?

NEC Tables provide ampacity based on conductor size and conditions.

Question 8 of 10

When sizing an OCPD for a motor, what must be considered in addition to the motor's full-load current?

Starting currents are significantly higher than running currents for motors.

Question 9 of 10

What type of overcurrent protection is typically used for branch circuits?

Fuses and circuit breakers are the primary overcurrent protection.

Question 10 of 10

What is the purpose of the overcurrent protection device for a feeder circuit?

The OCPD protects the conductors carrying power to the connected loads.

NEC: Overcurrent Protection Device Sizing Quiz