NEC 240 — Overcurrent Protection Practice Test 1

Question 1: The ampacity of the feeder tap conductors NOT MORE than 10 ft in length shall not be less than the rating of its terminating overcurrent device.

• True
• False

NEC Reference: NEC 240.21(B)(1)(1)

Question 2: Tap conductors that leave the enclosure or vault shall have an ampacity not less than ________ of the overcurrent device rating protecting the FEEDER conductors.

• 1/5
• 1/10
• 1/12
• 1/8

NEC Reference: NEC 240.21(B)(1)(4)

Question 3: The branch circuit  rated circuit breaker is marked for use with No 18 AWG and supplies a continuous load of 5.6 ampere, which of the following over current protection amperage that can be used?

• 7 amperes
• 10 amperes
• 15 amperes
• 20 amperes

NEC Reference: NEC 240.4

Question 4: The over current device should be connected in parallel with each ungrounded conductor.

• True
• False

NEC Reference: NEC 240.20(A)

Question 5: Normally over current devices are located in ungrounded conductors at a point where the conductors deliver the energy to the load.

• True
• False

NEC Reference: NEC 240.21

Question 6: Which of the following is the maximum voltage that a <strong>plug fuses</strong> are used as over-current protection devices in electric circuit?

• 150 volts
• 120 volts
• 240 volts
• 480 volts

NEC Reference: NEC 240.50(A)

Question 7: Which of the following is not a standard rating of a fuse or circuit breaker?

• 35
• 45
• 55
• 25

Question 8: When two different sizes of wire are connected in series, the maximum fuse rating that shall be used is one that protects .....................

• smallest wire
• largest wire
• both wires

NEC Reference: NEC 240.4

Question 9: Overcurrent protection is completely eliminated for tap conductors whose LENGTH does not exceed 25 feet.

• True
• False

NEC Reference: NEC 240.21

Question 10: Per NEC 240.4(D), what is the maximum overcurrent protection permitted for No. 14 AWG copper conductors in a branch circuit?

• 10 A
• 15 A
• 20 A
• 25 A

NEC Reference: NEC 240.4(D)(3)

Question 11: Per NEC 240.4(D), what is the maximum overcurrent protection permitted for No. 12 AWG copper conductors?

• 15 A
• 20 A
• 25 A
• 30 A

NEC Reference: NEC 240.4(D)(5)

Question 12: Per NEC 240.4(D), what is the maximum overcurrent protection permitted for No. 10 AWG copper conductors?

• 20 A
• 25 A
• 30 A
• 40 A

NEC Reference: NEC 240.4(D)(6)

Question 13: The diagram shows a 25 ft tap conductor running from a feeder to a subpanel. Per NEC 240.21(B)(2), the tap conductors must terminate in a single circuit breaker or set of fuses rated at no more than:

• The rating of the upstream (feeder) overcurrent device
• The ampacity of the tap conductors
• 125% of the continuous load
• 1/3 of the feeder overcurrent device rating

NEC Reference: NEC 240.21(B)(2)(3)

Question 14: Per NEC 240.21(B)(2), for the 25-foot tap rule to apply, the tap conductor ampacity shall be not less than what fraction of the upstream overcurrent device rating protecting the feeder?

• 1/10
• 1/4
• 1/3
• 1/2

NEC Reference: NEC 240.21(B)(2)(1)

Question 15: Per NEC 240.6(A), which of the following is NOT a standard ampere rating for fuses and fixed-trip circuit breakers?

• 60 A
• 65 A
• 70 A
• 80 A

NEC Reference: NEC 240.6(A)

Question 16: Per NEC 240.24(A), the center of the grip of a circuit breaker's operating handle, when in its highest position, shall not be more than _______ above the floor or working platform.

• 5 ft 6 in
• 6 ft 0 in
• 6 ft 7 in
• 7 ft 0 in

NEC Reference: NEC 240.24(A)(1)

Question 17: The cartridge fuse shown in the image has flat knife-blade contacts at each end. Per NEC 240.60(B), this type of contact indicates the fuse is rated at:

• 30 A or less
• Exactly 60 A
• 60 A or less
• Over 60 A

NEC Reference: NEC 240.60(B)

Question 18: Per NEC 240.22, overcurrent devices shall generally NOT be placed in series with which type of conductor?

• Ungrounded (hot) conductors
• Equipment grounding conductors
• Grounded (neutral) conductors
• All conductors equally

NEC Reference: NEC 240.22

Question 19: Per NEC 240.24(D), overcurrent devices shall NOT be located in the vicinity of easily ignitable material. Which of the following is the specific example given in the NEC?

• Attached garages
• Clothes closets
• Kitchen pantries
• Utility rooms

NEC Reference: NEC 240.24(D)

Question 20: The circuit breaker in the image has the marking "SWD" on its face plate. Per NEC 240.83(C), this breaker is listed and suitable for use as a switch on which type of circuit?

• Motor circuits rated 1 HP or less
• Fluorescent lighting circuits at 120 V or 277 V
• Electric resistance heating circuits
• HVAC compressor circuits

NEC Reference: NEC 240.83(C)

Question 21: Per NEC 240.10, supplementary overcurrent protection found inside luminaires or appliances:

• May substitute for the required branch-circuit overcurrent device
• Shall not be used as a substitute for required branch-circuit overcurrent protection
• Must be rated equal to the branch-circuit overcurrent device
• Requires a separate disconnecting means per NEC 430

NEC Reference: NEC 240.10

Question 22: Per NEC 240.4(B), when a conductor's ampacity does not correspond to a standard OCPD rating, the next higher standard device rating is permitted ONLY if the next higher rating does not exceed:

• 400 A
• 600 A
• 800 A
• 1,000 A

NEC Reference: NEC 240.4(B)

Question 23: Per NEC 240.80, circuit breakers shall be:

• Operable by automatic means only
• Capable of being opened and closed manually
• Equipped with a key-operated interlock
• Rated at a minimum of 30 A

NEC Reference: NEC 240.80

Question 24: Per NEC 240.51(B), Edison-base plug fuses shall be used only:

• In all new residential installations
• As replacements in existing installations where there is no evidence of tampering or overfusing
• In circuits up to 240 V
• In motor circuits up to 2 HP

NEC Reference: NEC 240.51(B)

Question 25: Per NEC 240.54(C), once a Type S fuse adapter is installed in a fuseholder, the adapter shall:

• Be removable with a standard screwdriver for future ampere-rating changes
• Be non-removable and accept only that specific ampere-class fuse
• Accept any ampere rating of Type S fuse
• Be removed before installing each replacement fuse

NEC Reference: NEC 240.54(C)

Question 26: The time-current characteristic curve shown has two devices: Curve A (current-limiting fuse) and Curve B (thermal-magnetic circuit breaker), both rated 100 A. At a fault current of 1,000 A (10× rating), which device clears the fault faster?

• Curve A — the current-limiting fuse
• Curve B — the thermal-magnetic circuit breaker
• Both clear in the same time at 1,000 A
• Cannot be determined from the curve alone

NEC Reference: NEC 240.2

Question 27: Per NEC 240.4(G), overcurrent protection for conductors supplying motor loads shall be provided in accordance with which NEC Article?

• NEC Article 210
• NEC Article 220
• NEC Article 430
• NEC Article 440

NEC Reference: NEC 240.4(G)

Question 28: Per NEC 240.85, a circuit breaker with a slash voltage rating of "120/240V" may be applied on:

• Ungrounded delta systems only
• Corner-grounded delta systems only
• Solidly grounded systems where voltage to ground does not exceed 120 V
• Any system where the line-to-line voltage does not exceed 240 V

NEC Reference: NEC 240.85

Question 29: Per the general rule in NEC 240.21(A), overcurrent protection shall be provided for conductors:

• At the point where they terminate at the load
• At the point where they receive their supply
• At the midpoint of the conductor run
• Only at the main service disconnect

NEC Reference: NEC 240.21(A)

Question 30: Per NEC 240.4(D), what is the maximum overcurrent protection permitted for No. 12 AWG aluminum or copper-clad aluminum conductors?

• 15 A
• 20 A
• 25 A
• 30 A

NEC Reference: NEC 240.4(D)(4)