Selecting power cables and circuit breakers for a WDM device

Q1: Which factors are important for selecting power cables with different specifications?
A1: Consider the following factors when selecting power cables with different specifications: ambient temperature, transmission distance, current size, input voltage, and minimum voltage of the device.
Q2: How do I calculate these factors?
A2: (I = P/U)
I: working current of the device, in the unit of A
P: maximum tested power consumption of the device, in the unit of W
U: rated working voltage of the device, in the unit of V
L: length of a loop of the power cable, in the unit of m. The value is determined by survey engineers.
ΔU: voltage drop value of a loop.
γ: conductivity of the copper conductor, with the value of 57 m/Ω.mm2. The conductivity of a copper clad aluminum (CCA) power cable is 36.557 m/Ω.mm2
S: section of the power cable conductor, in the unit of mm2. The value is a rounded up integer. For example, the calculated section of 14.8 mm2 is rounded up to 16 mm2.
Q3: I have a subrack that only its optical layer is used or has been fully configured. I do not need high current circuit breakers. How can I calculate them?
A3: Circuit breakers = 1.2 x Maximum possible power consumption of the subrack/Minimum voltage (38.4)
The value is a rounded up integer. For example, if the calculated current is 11 A, the minimum circuit breaker can be 16 A.