How can two 30 amp breakers equal 30 amps? Well, 30 amps is 30 amps. Voltage and current are two different aspects of electricity. Using two legs on different phases does not change the amperage but does change the voltage. To put this into an analogy of water, current is the volume and voltage is the pressure. If there is more voltage or more current there is more power. Using a 240 volt 30 amp circuit delivers twice the power of a 120 volt 30 amp circuit but it is still a 30 amp circuit. As the voltage is increased the amount of current needed to do the same work is decreased. This is the reason why power transmission lines run at very high voltages. It's all rather strange but the amount of energy loss is dependent on current not voltage, I2r and all that. This is also why large appliances use 240 volt instead of 120. Everything gets smaller. The breaker size, the wire size, the line loss, etc, but the same amount of power is transmitted. At the facilities that I oversee everything electrical / electronic we use all kinds of voltages from 12470 on down.