Q. Can you please go over the basic rules for feeder taps?

A. Certainly. These rules are found in 240.21(B), and are different, depending on the length of the tap.

Feeder tap conductors up to 10 ft long are permitted without overcurrent protection at the tap location if installed as follows:

  1. The ampacity of the tap conductor must not be less than:
    • The calculated load in accordance with Art. 220, and
    • The rating of the device or overcurrent device supplied by the tap conductors.
  2. The tap conductors must not extend beyond the equipment they supply.
  3. The tap conductors must be installed in a raceway if they leave the enclosure.
  4. The tap conductors must have an ampacity not less than 10% of the ampacity of the overcurrent device that protects the feeder. FPN: See 408.36 for the overcurrent protection requirements for panelboards.
Feeder tap conductors up to 25 ft long are permitted without overcurrent protection at the tap location if installed as follows:
  1. The ampacity of the tap conductors must not be less than one-third the ampacity of the overcurrent device that protects the feeder.
  2. The tap conductors terminate in a single circuit breaker, or set of fuses rated no more than the tap conductor ampacity in accordance with 310.15 [Table 310.16].
  3. The tap conductors must be protected from physical damage by being enclosed in a manner approved by the AHJ, such as within a raceway.
Feeder tap conductors that supply a transformer must be installed as follows:
  1. The primary tap conductors must have an ampacity not less than one-third the ampacity of the overcurrent device.
  2. The secondary conductors must have an ampacity that, when multiplied by the ratio of the primary-to-secondary voltage, is at least one-third the rating of the overcurrent device that protects the feeder conductors.
  3. The total length of the primary and secondary conductors must not exceed 25 ft.
  4. Primary and secondary conductors must be protected from physical damage by being enclosed in a manner approved by the AHJ, such as within a raceway.
  5. Secondary conductors must terminate in a single circuit breaker, or set of fuses rated no more than the tap conductor ampacity in accordance with 310.15 [Table 310.16].
Outside feeder tap conductors can be of unlimited length, without overcurrent protection at the point they receive their supply, if installed as follows:
  1. The tap conductors must be suitably protected from physical damage in a raceway or manner approved by the AHJ.
  2. The tap conductors must terminate at a single circuit breaker or a single set of fuses that limits the load to the ampacity of the conductors.
  3. The overcurrent device for the tap conductors must be an integral part of the disconnecting means, or it must be located immediately adjacent to it.
  4. The disconnecting means must be located at a readily accessible location, either outside the building or structure, or nearest the point of entry of the conductors.