Section 240.21(B) has the requirements for installation of feed tap which is what you have described. This requirement does permit conductor (feeders) to be tapped without overcurrent protection at the tap.
240.21(B)(1) does permit the tap conductor to be terminated to MLO panel, if the tap conductors does not exceed 10 ft and the tap conductors comply with all of requirements.
(1) The ampacity of the tap conductors is
a. Not less than the combined calculated loads on the circuits supplied by the tap conductors, and
b. 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.
(2) The tap conductors do not extend beyond the switchboard, panelboard, disconnecting means, or control devices they supply.
(3) Except at the point of connection to the feeder, the tap conductors are enclosed in a raceway, which shall extend from the tap to the enclosure of an enclosed switchboard, panelboard, or control devices, or to the back of an open switchboard.
(4) For field installations where the tap conductors leave the enclosure or vault in which the tap is made, the rating of the overcurrent device on the line side of the tap conductors shall not exceed 10 times the ampacity of the tap conductor.
The (2) taps not over 25 ft, (3)taps supplying a transformer [Primary Plus Secondary Not over 25 ft Long], (4) taps over 25 ft, and (5) outside taps of unlimited length are required the terminate at a single circuit breaker or a single set of fuses that limit the load to the ampacity of the conductors.
