A magnetic breaker trips when the strength of the magnetic force exceeding the force exerted by a spring. The megnetic force is determined by the ampere turns in the coil exerting the megnetic force. The only impact that the voltage has on this is with resistive loads is that the voltage goes up, so does the current. E=IR. E is voltage, I is current, R is resistance. With the thremal breakers, the heat generated by power flowing through a bi-metallic element causes the breaker to open. The advantage of the thermal breaker is that it is heat that will damage the transformer. So a thermal breaker can be specified to match the increase in heat in the transformer. Since it takes time for the heat to build up, the thermal breaker will allow high current loads for short periods of time. This has the advantage of getting motors to start spinning, which are started by closing contacts and applying line voltage to start motors. Toy trains are subject to many short circuit situations due to the power being in exposed adjacent rails. It is desirable for toy train power supplies to be protected with magnetic breakers to quickly interrupt these short circuits. But the transformer manufactures installed thermal breakers in the transformers to protect the transformer winding leaving it up to the toy train operator to provide circuit protection to protect the trains. In the postwar era Lionel provided the 91 circuit breaker for this. Most operators never used any additional protected and survived to talk about it. The important thing is to never leave trains energized and unattended. Now that trains are in the electronic era there are new protective devices and new problems. A whole new era.
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