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In theory, the voltage across a wire is zero, so any components bypassed by a short circuit can be ignored when analyzing the circuit.

A real wire, however, is not an ideal conductor. Is there any real-world situation where you would have a circuit where a component is deliberately short-circuited?

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  • \$\begingroup\$ Does a reset-line that is driven low with open collector outputs from several sub-ciruits count? \$\endgroup\$ – jippie Oct 1 '14 at 5:39
  • \$\begingroup\$ Sometimes parts of a circuit may be "disabled" by the (hobbyist) user by putting a jumper at a certain location. Voltage regulators come to my mind, which either allow to use e.g. 5V supply, or a direct 3.3V supply, bypassing the regulator. Sometimes instead of jumpers solder bridges are be used. That's for hobbyist or prototype use, of course; typically, in volumes, one would not include parts in a circuit which may be permanently bypassed in the product anyway. \$\endgroup\$ – JimmyB Oct 1 '14 at 14:21
  • \$\begingroup\$ However, in some circuit digrams such constructs can be found, usually indicating that the bypassed part may later be populated only for certain variants of the circuit and omitted on others. \$\endgroup\$ – JimmyB Oct 1 '14 at 14:24
  • \$\begingroup\$ Some times inputs are pulled up with a resistor and the short circuit pulls it low (or vice versa ) Used to turn on or off features or set addresses in that are set once and never changed. \$\endgroup\$ – Spoon Oct 1 '14 at 21:20
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I worked with a guy who liked to do this:

schematic

simulate this circuit – Schematic created using CircuitLab

In normal operation the LED is short circuited. If the fuse blows you've got a nice indicator to tell you why your circuit suddenly stopped working.

I can't say I'm 100% sure of the wisdom of continuing to run current through the load once it's had a fault that makes it blow a fuse though.

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  • \$\begingroup\$ There are car fuses that use this exact setup to indicate the fuse blew. \$\endgroup\$ – Passerby Oct 1 '14 at 5:14
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    \$\begingroup\$ I have several commercially made fuse holders that are similar, but they used neon indicators instead of an led. The trick to designing such a circuit is to choose a resistor value high enough to protect your wiring when the load is shorted, low enough to keep your indicator lit when the short is fixed, high enough to disable the load when the fuse is blown and the circuit to work over the entire range of possible load resistances. If your coworker did all this he is an EE to be reckoned with. Much easier to do with neon which is high impedance but it is only suitable for high voltage. \$\endgroup\$ – hildred Sep 17 '16 at 6:06

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