Stumped by the Code? NEC Requirements for 10-Ft Tap Rules

June 19, 2015

Your most pressing National Electrical Code (NEC) questions answered

All questions and answers are based on the 2014 NEC.

Q. Please explain the 10-ft tap rules?

A. Except as permitted by Sec. 240.21(A) through (H), 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) (see Fig. 1).

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Fig. 1. Except as permitted by (A) through (H), overcurrent devices must be placed at the point where the conductors receive their power.

Branch circuit taps are permitted in accordance with Sec. 210.19 [240.21(A)].

Conductors can be tapped to a feeder as specified in Sec. 240.21(B)(1) through (B)(5). The “next size up protection rule” of Sec. 240.4(B) isn’t permitted for tap conductors [240.21(B)] (see Fig. 2).

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Fig. 2. Conductors can be tapped to a feeder as specified in Sec. 240.21(B).

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 [240.21(B)(1)]:

The ampacity of the tap conductor must not be less than [240.21(B)(1)(1)]:

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

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

Exception: Listed equipment, such as a surge protection device, can have their conductors sized in accordance with the manufacturer’s instructions.

The tap conductors must not extend beyond the equipment they supply [240.21(B)(1)(2)].

The tap conductors are installed in a raceway when they leave the enclosure [240.21(B)(1)(3)].

The tap conductors must have an ampacity not less than 10% of the rating of the overcurrent device that protects the feeder [240.21(B)(1)(4)].

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

Here’s an example problem that helps better explain how to apply these rules.

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

200A disconnect: 3/0 AWG is rated 200A at 75°C, and is greater than 10% of the rating of the overcurrent device (400A).

150A disconnect: 1/0 AWG is rated 150A at 75°C, and is greater than 10% of the rating of the overcurrent device (400A).

30A disconnect: 8 AWG is rated 40A at 60°C. The tap conductors from the 400A feeder to the 30A overcurrent device can’t be less than 40A (10% of the rating of the 400A feeder overcurrent device).

Holt is the owner of Mike Holt Enterprises, Inc. in Leesburg, Fla. He can be reached at www.mikeholt.com.

About the Author

Mike Holt

Mike Holt is the owner of Mike Holt Enterprises (www.MikeHolt.com), one of the largest electrical publishers in the United States. He earned a master's degree in the Business Administration Program (MBA) from the University of Miami. He earned his reputation as a National Electrical Code (NEC) expert by working his way up through the electrical trade. Formally a construction editor for two different trade publications, Mike started his career as an apprentice electrician and eventually became a master electrician, an electrical inspector, a contractor, and an educator. Mike has taught more than 1,000 classes on 30 different electrical-related subjects — ranging from alarm installations to exam preparation and voltage drop calculations. He continues to produce seminars, videos, books, and online training for the trade as well as contribute monthly Code content to EC&M magazine.