Richard, in the example you have given you are wrong i am afraid to say.
Voltage drop can only be calculated along the entire length of a circuit for design purposes. In your example the Voltage drop on the supply to the JB is ZERO because to measure this properly you need to disconnect from the branch to avoid loading by the installed fittings, and as there would be no load then there would be no volt drop.
This section of the circuit will suffer the maximum voltage drop on the circuit, the voltage drop on the branch sections is irrelevant in this example because the circuit should be designed to take into account all the volt drop along it's length.
This is why we use the equation VD=Mv/A/m
OK I will respond, but I think it will not be worth it, in the information you give above you are jumping from measurement to calculation.
I agree that if you were to
measure volt drop at the junction box with with the loads disconnected you would
measure zero.
Then you go on to say that this section with suffer max volt drop, despite it reading zero in measurement.
However I agree that the calculated volt drop would be under the most onerous conditions (i.e. maximum current flow) along that length.
I do not agree that it is the
maximum volt drop because if it was a 1m length of cable taking 10A, and the rest of the circuit was a 100m length of the same cable taking 0.5A (assuming the 9.5A remainder were used at the JB) the volt drop proportion would be five times greater over the long part of the circuit.
Could you let me know how you would calculate volt drop where the circuit has differing sizes of cable.
I also notice in your calculations in later posts that on summing the individual volt drops (that you state as incorrect) you miss out the volt drop on the supply cable, presumably you are assigning this as zero?
(This would not affect your "proof", the calculation would still come out with a higher volt drop by your method)
Anyway an interesting diversion, I will not go further as the horse is at the water.
(Sorry you were subjected to this Monkeyblaine)