1. The problem statement, all variables and given/known data I am looking for a general explanation of when the total reluctance of a magnetic circuit is not equivalent to the sum of the reluctances if each area. In several examples the text has added 2 areas in parallel and then added the third area. I'm not 100% sure on when this is required. 2. Relevant equations I use R=l/(μA) to determine the reluctance of each area, but don't know if/when reluctances need to be added in parallel. 3. The attempt at a solution For example, if I have a shape like this: where the shaded region is air and the rest (the white area) is iron, I calculated the reluctance for the left, middle, right and small air gap. However, is the total the simple addition of them or are the left and right "legs" in parallel?