I'm looking at current readings from each branch in a fairly simple parallel circuit, and I'm trying to make sure that I am correctly diagnosing the problem based on the trends that I'm seeing in the data.

I have a constant voltage source and a number of branches in parallel. Each branch has a resistor in the form of a fuse. One of the fuses blows and creates an open circuit. In this situation, the resistance on the branch with the blown fuse should approach infinity, current on that branch drops to zero, and the total resistance of the circuit increases.

My question is this: What effect, if any, does an open circuit on one branch have on the current flow in the other branches in the parallel circuit? In my data trends, I'm seeing a drop in current from the rest of the branches in the circuit that I believe was caused by the blown fuse. V=IR, so an increase in total resistance should be accompanied by a decrease in total current to maintain constant voltage. But I would think that the decrease in total current would strictly come from the complete loss of current on the branch with the blown fuse, and that the current in the other branches would be unaffected. Am I not understanding something correctly here?

  • $\begingroup$ Are the fuses of identical resistance? $\endgroup$ – HiddenBabel Oct 7 '18 at 19:32

I you have an ideal voltage source, the current through each branch is independent on the currents in any other branch. If a fuse blows, the current in that branch should go to zero, the other branch currents remain unchanged and the total current goes down by the amount of current from the broken branch.

In practice, this depends on the source impedance of your voltage source. If you have a very "stiff" or regulated supply, the source impedance is very small and the voltage is independent of current. If you have supply with source impedance that's within two orders of magnitude of the branch impedance, you will see some "voltage droop", i.e. the voltage will go down a bit as the total current increases and go up a bit if the total current decreases. In that case you would see the branch currents slightly increasing if one branch blows a fuse.

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