Lesson 7: Special Conductor Overcurrent Protection Permitted, Including Taps (2023)

A 3/0 AWG copper feeder conductor is tapped with 20 feet of 2 AWG conductor. What is the maximum OCPD size allowed at the termination of the tap conductors installed in a fused switch or circuit breaker? (All conductors and terminations are rated 75°C.)

110 A Note: NEC 240.21(B) does not allow the use of 240.4(B), known as the round-up rule. The 2 AWG conductor ampacity from Table 310.16 is 115 amperes. The standard rating for OCPDs shown in 240.6(A) would therefore require a 110-ampere OCPD to be used.

An existing 50-ampere branch circuit is located in a kitchen for the connection of cooking equipment. A tap conductor is used to supply a new wall-mounted oven and a new counter-mounted cooking unit. The wiring method used between the 50-ampere junction box and the new cooking equipment is Type NM cable. What is the minimum size conductor and maximum conductor length allowed by the Code for this installation?

12 AWG, unlimited length, but not longer than necessary Note: NEC 240.21(A) references 210.19, and this type of installation is addressed by 210.19(A)(3) Exception No. 1.

Indicate whether feeder taps of 20 feet are covered or not covered in each of the following NEC sections.

240.21(A) → Not covered 240.21(B)(1) → Not covered 240.21(B)(2) → Covered 240.21(B)(3) → Covered 240.21(B)(4) → Not covered 240.21(B)(5) → Covered

Feeder taps not over 10 feet long are covered by ? .

240.21(B)(1)

The NEC permits a set of conductors feeding a single load, or each set of conductors feeding separate loads, to be connected to a transformer secondary without overcurrent protection at the secondary, as specified in ? .

240.21(C)(1) through (C)(6)

A back-up power generator is provided to supply back-up power to two subpanels though a transfer switch. The nameplate of the generator shows a 200-ampere, 240-volt, single-phase system connected from a 200-ampere main circuit breaker located on the generator. The subpanels are located eight feet away from the wireway where the taps are located, and each panel contains a 100-ampere main MCCB. A 3/0 AWG THWN-2 copper conductor is used to connect to the utility power source, the generator, and the wireway. Using the 75°C column of Table 310.16, what is the minimum size THWN-2 copper conductor permitted from the wireway to each panel?

3 AWG Note: Please refer to NEC 240.21(B)(1).

Tap conductors shall be permitted to be protected against overcurrent in accordance with ? .

A.) 210.19(A)(4) B.) 240.21 C.) 368.17(B) D.) 430.53(D) All of the above NEC Reference: 240.4(E)

Which of the following is true regarding the 10-foot tap rule where the ampere rating of the OCPD protecting the tap on the line-side connection is 250 amperes?

A.) For field-installed tap conductors that leave the enclosure in which the tap was made, the tap conductor's ampacity is not less than 1/10th of the OCPD ampere rating that is protecting the feeder conductors. B.) The ampacity of the tap conductor is not less than the ampere rating of the OCPD at the termination of the tap conductor, or is not less than the rating of the equipment containing an overcurrent protective device(s) supplied by the tap conductor. C.) The ampacity of the tap conductor is not less than the calculated load of the loads supplied by the tap conductor. D.) The tap conductors are enclosed in raceway if run external of an enclosure. All of the above

In an industrial installation, three separate 400-ampere bus duct taps, each 40 feet in length, are permitted to be tapped from a 1,200-ampere busway protected by a 1,200-ampere OCPD.

Acceptable Note: NEC 240.21(E) and 368.17(B) permit this installation, provided the taps do not contact combustible material.

A 150-ampere feeder conductor is installed outside the building in a metal wireway. A 60-ampere tap conductor is installed from the metal wireway to a new garage building located 100 feet away from the original building. A 60-ampere fused disconnecting means is provided outside the new garage. The tap conductors are protected from physical damage by a rigid metal conduit.

Acceptable Note: Please refer to NEC Reference: 240.21(B)(5).

A 25-foot, 4 AWG, 75°C, copper conductor could be tapped from a 3/0 AWG 75°C, copper feeder conductor protected by a 200-ampere OCPD if the 4 AWG conductor terminates in an 80-ampere OCPD and the tap conductors are protected from physical damage by being enclosed in an approved raceway.

Acceptable Note: The 4 AWG conductor ampacity is 85 amperes and is not less than 1/3 of the OCPD rating protecting the 3/0 AWG conductor, which has an ampacity of 200 amperes. The minimum tap conductor ampacity in this case is 67 amperes (200 ÷ 3 = 67). This tap is permitted, provided the 4 AWG conductors terminate in a single circuit breaker or set of fuses not more than 85 amperes.

NEC 240.21, with some exceptions, requires overcurrent protection in each ungrounded conductor to be located where the conductors connect to the load.

False Note: NEC 240.21, with some exceptions, requires overcurrent protection in each ungrounded conductor to be located where the conductors receive their supply.

Section 240.21 provides specific 10-foot and 25-foot tap rules for service conductors.

False Note: Service conductors are permitted to be tapped as per 230.46. Always check with the local utility for allowed service conductor tap rules.

Conductors, other than flexible cords, flexible cables, and fixture wires, are required without exception or other permission to be protected against overcurrent in accordance with their ampacity specified in 310.14 at the source connection point of the conductor.

False NEC Reference: 240.4 Note: Seven exceptions to this general rule are recognized in 240.4(A) through (G).

A ? conductor is a conductor, other than a service conductor, that has overcurrent protection ahead of its point of supply that exceeds the value permitted for similar conductors and is protected as described elsewhere in 240.4.

Tap NEC Reference 240.2

Which of the following is not a required item for tap conductors over 25 feet long used in a high bay manufacturing building over 35 feet high at the walls?

The tap conductors are sized 8 AWG copper or 2 AWG aluminum or larger.

A service conductor is never a tap conductor.

True

Once a feeder conductor has been tapped with smaller tap conductors serving downstream equipment, it is not permissible to apply a second tap on the first tap. (In essence, do not tap a tap.)

True NEC Reference: 240.21

Overcurrent protection shall be permitted to be installed as close as practicable to the storage battery terminals in an unclassified location.

True NEC Reference: 240.21(H)