The change in 240.21(B)(1)(1)(b) makes it clear that the tap conductor ampacity cannot be less than the rating of the equipment containing an overcurrent device(s) supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors.
The previous code language allowed the tap conductor ampacity to be rated no less than the “device” supplied by the tap conductors. This was misleading and opened the door to the idea that a tap conductor could be without any overcurrent protection at the load end of the conductor if it supplied a device rather than an overcurrent device.
A new exception was also added to address tap conductors supplying listed equipment such as surge protective devices (SPD). For these types of devices, simply follow the manufacturer’s installation instructions.
Below is a preview of the NEC. See the actual NEC text at NFPA.ORG for the complete code section. Once there, click on the “free access” tab and select the applicable year of NFPA 70 (National Electrical code).
2011 Code Language:
240.21(B)(1).
(1) The ampacity of the tap conductors is:
Not less than the combined calculated loads on the circuits supplied by the tap conductors, and
Not less than the rating of the device supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors.
2014 Code Language:
240.21(B)(1).
(1) The ampacity of the tap conductors is:
Not less than the combined calculated loads on the circuits supplied by the tap conductors, and
Not less than the rating of the equipment containing an overcurrent device(s) supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors.
Exception to b: Where listed equipment, such as a surge protective device(s) [SPD(s)], is provided with specific instructions on minimum conductor sizing, the ampacity of the tap conductors supplying that equipment shall be permitted to be determined based on the manufacturer’s instructions.
