I have a question that could be appropriate only for Physics Stack Exchange (and not for EESE), so I thought it would be a good idea to post it here on meta, so I could get a confirmation. Here goes the body of said question:

A bit of context

I came up with this question after someone suggested that two fuses are better than a main one in the below configuration. The converters are SMPSs which regulate output voltage.


Now someone justified that F1 and F2 are a better implementation through the following example: both converters are functioning within normal limits, each drawing 1A (and F1 and F2 are both designed to trip at 2A). If Converter 1 would fail open and Converter 2 would continue working normally, then during the finite instant when the aforementioned conditions start applying, as current cannot change instantly and has only one path to follow from supply to ground, the 2A will flow through Converter 2 and potentially damage it. Since F2 is there, it would protect against the over-current condition. If converters reverse roles in the same scenario, F1 will be there to open the circuit.

The justification basically says that the fuses are there to protect against an open-circuit event...instead of a short-circuit.

Main part

Now, remove the converters and the loads and place two real-world resistors between each fuse and ground, both (resistors) drawing 1A normally. Again, the total current drawn from the power supply would be 2 A.

The questions are:

1) If one removes a resistor (ceteris paribus), will the remaining other experience the 2A through for a very short, but finite amount of time? If it does, can it be due to something else, other than parasitic inductance?

2) Does 1) mean, if true, that ohm's law only applies if the time-step (or time scale) is large enough?

3) If 1) is true, is it worth taking into account this effect from an engineering perspective-i.e. during that short finite time, the 2A could damage the remaining resistor?


1 Answer 1


This would be fine for EE. Probably a bit too specific for Physics.

But you'll have to provide more context. "Someone justified" is not adequate. Where did this statement come from?

  • \$\begingroup\$ Thanks for answering, I have polished the part with the justification and it should be alright now. If you give me the green light, I'll go ahead and post it. \$\endgroup\$ Commented Feb 3, 2020 at 10:25
  • \$\begingroup\$ That isn't what I meant. Who was the "someone", and where did "current cannot change instantly" statement come from? It appears to be a false premise, and we need to know how to address your misunderstanding. Was "someone" talking about parasitic effects (inductance), or perhaps thinking of transmission lines? Go ahead and post the question and we can start working on it. \$\endgroup\$
    – Dave Tweed
    Commented Feb 3, 2020 at 12:35

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