Short Taps From A Feeder

Sometimes, the feeder passes quite close to the motor location. The motor circuit tap from the feeder is required by Article 240-21 to have overcurrent protection at its input. However, under some conditions with minimum exposure to short-circuits, this requirement can be amended to avoid the need for this device. This is an important provision of the NEC that requires careful application. Exception No. 6 (the "25-foot rule") permits the use of smaller tap-offs to individual motors without overcurrent protection at the input to the tap-off when ALL of the following conditions are met:

1. The tap-off conductors must be correctly sized for the motor (i.e., 125% of rated full-load current at the operating temperature).
2. The ampacity of the tap must not be less than one-third of the ampacity of the feeder or branch circuit conductors from which the tap is taken.
3. The tap must not be longer than 25 feet from the tap to the motor's running overcurrent device.
4. The tap-off must terminate in a single device.
5. The conductors must be protected against mechanical abuse.

Article 430-28 permits smaller conductors for motor taps if sized for the motor and not longer than 10 feet, and if enclosed in an appropriate raceway or controller enclosure.

You should also note that a tap with conductor ampacities equivalent to those of the feeder from which it is being tapped has as much ampacity as the feeder itself. Therefore, it is protected by the same overcurrent device that the feeder uses. This is true regardless of the length of the tap. Likewise, a smaller conductor does not require a separate overcurrent device from the feeder if the feeder overcurrent device is set for the ampacity of the smaller conductor. This is sometimes part of the design when oversize conductors are used for a feeder to reduce voltage drop. Even though oversizing conductors this way would permit the omission of protection, some designers provide short-circuit protection there anyway at the input to the branch circuit.