2011 Changes to the NEC – 240.21

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• Each Code section which contains a change includes a summary of the change, followed by a paraphrase of the NEC text affected by the change. Any specific change is denoted by underlined text and in the corresponding chapter color
• Graphics with green borders and 2011 CC icons next to the heading are graphics that contain a 2011 change; graphics without a green border or icon are graphics that support the concept being discussed, but nothing in the graphic was affected by a 2011 Code change.

240.21(B)(1)(4) 10-Foot Feeder Tap

An editorial revision has been made to provisions for sizing a 10 ft feeder tap conductor.

240.21 Overcurrent Protection Location in Circuit.

Except as permitted by (A) through (G), overcurrent devices must be placed at the point where the branch circuit or feeder conductors receive their power. Taps and transformer secondary conductors aren’t permitted to supply another conductor (tapping a tap isn’t permitted).

Figure 240-7 (Click on image to enlarge)

(B) Feeder Taps. Conductors can be tapped to a feeder as specified in 240.21(B)(1) through (B)(5).

(1) 10-Foot Feeder Tap. Feeder tap conductors up to 10 ft long are permitted without overcurrent protection at the tap location if the tap conductors comply with the following:

(1) The ampacity of the tap conductor must not be less than:

a. The calculated load in accordance with Article 220, and

b. The rating of the device or overcurrent device supplied by the tap conductors.

Figure 240-8 (Click on image to enlarge)

(2) The tap conductors must not extend beyond the equipment they supply.

(3) The tap conductors are installed in a raceway if they leave the enclosure.

(4) If the tap conductors leave the enclosure or vault in which the tap is made, the tap conductors must have an ampacity not less than 1/10th of the rating of the overcurrent device that protects the feeder.

Note: See 408.36 for the overcurrent protection requirements for panelboards.

Example: A 400A breaker protects a set of 500 kcmil feeder conductors. There are three taps fed from the 500 kcmil feeders that supply disconnects with 200A, 150A, and 30A overcurrent devices. What are the minimum size conductors for these taps?

Figure 240-9 (Click on image to enlarge)

• 200A: 3/0 AWG is rated 200A at 75°, and is greater than 10 percent of the ampacity of 500 kcmil, which is rated 380A at 75°.
• 150A: 1/0 AWG is rated 150A at 75°, and is greater than 10 percent of the ampacity of 500 kcmil, which is rated 380A at 75°.
• 30A: 8 AWG is rated 50A at 75°, and is greater than 10 percent of the ampacity of 500 kcmil, which is rated 380A at 75°. Anything smaller than 8 AWG can’t be used, as it will have an ampacity of less than 10 percent of 380A (38A) in the 75° column of 310.15(B)(16).

ANALYSIS: Previous editions of the Code have required that the overcurrent device upstream of the feeder tap not exceed 10 times the ampacity of the conductor. This revision changes the wording to require that the conductor have an ampacity of not less than 1/10 the rating of the overcurrent device. This results in no technical change whatsoever, but provides a section that’s easier to read. It also brings the NEC text into alignment with the existing text of 240.21(B)(2)(1).

 

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