Been doing some reading and want to make sure I understand-

If there are from 7 to 9 current carrying conductors in a raceway, the maximum allowed current is 70% of the rating for the conductor.

For example, I installed 4- 120v branch circuits (8 conductors) which left the panel in one conduit before splitting off in different directions.

12 GA THHN/THWN is rated at 25A, & 70% is 17.5A, meaning each branch must be connected to a 15A breaker.

I found this to be surprising as I had assumed that a larger conduit would circumvent the need for derating.

Am I applying this correctly?