leaDCalc 4+

Application based on the Western Electric Co. Inc, Bell Laboratories, Bell System DC Power Lead Calculator which is in a circular slide rule format.  
Using allowable voltage drops specifically designed for telephone company central office direct current power plants and distribution wiring. The application references 48 volt battery systems but also works for other direct current voltages such as 24 volt. When using for 24 volts or other, choose by the required loop voltage drop instead of the specific section of the circuit.
Notes:
51. Voltage drop and wire size calculations are based on 2.00 volt LOOP drop from the power plant battery to the load equipment and return. 1.75 Final Volts Per Cell or 40 volts min. operating volts at the equipment for nominal 48V systems.
 (40 + 2 = 42 / 24 = 1.75fvpc) 


52. LOOP length is used in the calculations, often the battery and returns are unequal length. The result VD is shown as ONE WAY.


53. The formula used in the lead size calculations is:
CM = LoopLength * 11.1 * Fuse or Breaker @ 100% / VD
(T-Mobile does use 80% of the input breaker or fuse size to calculate DC power wires)
CM = LoopLength * 11.1 * Fuse or Breaker @ 80% / VD
For example the Bell System might use the leaDCalc recommended 66% of the input breaker or fuse size to calculate DC power wires.
The Bell System terms Peak and Busy Hour are antiquated electro-mechanical switch central office terms so leaDCalc recommends using 66% of the input fuse or breaker size, ie. 600A fuse or breaker calculate using 400 amperes and which is exactly as was done at Western Electric Co., Inc. for Bell System Telephone offices.
54. BDFB is a Battery Distributing Fuse Board. Fuse Panel is rack mounted at or near the load equipment. Load Equipment is the actual device requiring power. 


55. This application is intended for informational use. Based on the original Bell System Lead Calculator, Western Electric Co., Inc. Model GS-5420, 4-66.


56. "leaDCalc" is NOT affiliated with any person or company or anything else anywhere. No how, no way. 
Especially NOT T-Mobile nor the Bell System or even Western Electric Co. Inc., all of whom are mentioned. 
This application is meant as a guide only in determining the size and or capacities of power wiring used in direct current (DC), charging and storage battery telephone systems. 
This application is NOT intended to decide what type of wire, (or if you should even use wire or busbars in your DC systems), no how, no way and it is not for use with alternating current (AC) systems.