In US electrical breaker boxes there are two legs of AC power in opposite phase. This means that they each have 120V of potential relative to neutral or ground, and 240V potential relative to each other. Using a multimeter testing for AC voltage you can determine which breakers are associated with each leg. As long as the breaker terminals read 0V between them and not 240V between them, you can wire those breakers together to achieve the sum of their amperage limits rather than buying a large breaker. Four 20A breakers with 0V potential between them function as one 80A breaker when wired together. Remember though, that while 10 gauge wire is suitable from breaker to junction in this scenario, the wire downstream will need to be adequately sized for the full 80A current payload!