During normal operating conditions, how is dynamic brake retarding force limited?

The limiting of dynamic brake retarding force during normal operating conditions occurs primarily through the number of operative dynamic brake axles. This is because the effectiveness of dynamic braking is directly related to how many axles are equipped and actively participating in the dynamic braking process.

Dynamic braking operates by utilizing the traction motors of the locomotive, which generate electricity as they are driven by the train's momentum, effectively acting as generators. The braking force generated is proportional to the amount of power that can be managed and dissipated by the dynamic brake system. When there are fewer dynamic brake axles that are functioning, this will diminish the overall retarding force that can be applied to slow the train down.

Thus, if a locomotive has limited operative dynamic brake axles — whether due to mechanical issues or design limitations — it inherently restricts the total retarding force available when using dynamic braking.

Adjusting the brake handle position, increasing the speed of the locomotive, or checking brake pressure levels do not serve to limit the retarding force itself, but rather affect how brakes are engaged or how the system operates under different conditions, making them secondary factors in the context of dynamic brake force limitations.