What is the maximum operative axle weight of dynamic brake to avoid isolating a unit for fuel conservation?

The maximum operative axle weight of dynamic brake to avoid isolating a unit for fuel conservation is established to maintain efficiency during train operations. Having a limit, such as 400 tons, ensures that the dynamic braking system functions effectively without overloading the units, which can lead to inefficiencies and increased fuel consumption.

By keeping within this parameter, crews can optimize the train's braking performance while minimizing wear and tear on equipment, thus maintaining better operational control. Exceeding this weight could necessitate isolating the unit to prevent damage or unsafe conditions, ultimately leading to higher operational costs and lower fuel efficiency. This makes the choice of 400 tons the correct answer as it strikes the right balance between braking effectiveness and cost management.