One-pole 120V breakers only require a single slot around the panel. Double-pole 240V breakers have to have two slots. Tandem breakers be a part of two 120V circuits in one slot, which is useful for smaller electric powered panels. changing an electrical panel, evaluate the type, amperage and circuit breakers https://electricianclearwater12984.bloggazza.com/32334007/helping-the-others-realize-the-advantages-of-electrical-service