I am trying to describe the best I can the scenario I came up with in order to try to understand a short circuit.

Let’s say there is only one main circuit breaker and there are two outlets in the room.

Let’s say that outlet 1 gets short circuited by a cable that is cut on an Air conditioning unit.

Outlet two has a gfci type circuit breaker or a detachable circuit breaker with extra outlets ( An outlet extender with a circuit breaker)

Now to my understanding when a short circuit happens there is high amperage flowing through the circuit until the main circuit breaker pops and shuts off the power.

Now in those milliseconds of time between the short circuit happening and the circuit breaker popping, theoretically there is ALOT of amperage going around on the main circuit until the main circuit breaker pops.

This includes the excess amperage traveling through outlet 2. Theoretically shouldn’t the outlet with the circuit breaker pop as well as the main breaker since it is experiencing the flowing of extra amperage as well and by turning off and cutting electricity from outlet 2 help the devices that could be connected to it not get their power supplies / components damaged since it is closer.

Even if it does not pop should it not help since it is isolating a sub circuit from the main circuit that is experiencing the extra amperage.

  • \$\begingroup\$ Usually the main breaker is much higher rating than the branch circuits, and has a slower "break" time specifically to allow the lower value breaker to open before the larger main breaker. \$\endgroup\$
    – Ron Beyer
    Nov 23 '19 at 0:01
  • \$\begingroup\$ So would the devices on outlet 2 benefit from the second small circuit breaker if outlet 1 shorts and prevent damage if it were to happen? \$\endgroup\$
    – j w
    Nov 23 '19 at 0:05

If the cable plugged into outlet 1 is shorted, a high current will flow through the main breaker, outlet 1, the faulty cable, and the wiring in the wall between outlet 1 and the main breaker. High current will not flow through outlet 2, but both outlet 1 and outlet 2 will lose power when the main breaker trips.

In house wiring, all outlets on a circuit are wired in parallel, so all outlets see the same voltage. The current through each branch of a circuit will only depend on the load on that branch.



simulate this circuit – Schematic created using CircuitLab

In the above circuit, if Lamp 3 develops a short, a large current will flow through the top and bottom horizontal wires, and through F4 and lamp 3. This should blow fuse F4. The currrents through Lamps 1 and 2 will not be affected by the large current going to lamp 3.

In practice, depending on the characteristics of F1 and F4, F1 may blow before F4, then the whole circuit looses power. At no time does the high current through the shorted lamp 3 cause an increased current in lamps 1 and 2, so their fuses will not blow.

  • \$\begingroup\$ Suppose that they were connected and not wired in parallel, would my theory then work? \$\endgroup\$
    – j w
    Nov 23 '19 at 0:32
  • \$\begingroup\$ Just curious as to this situation \$\endgroup\$
    – j w
    Nov 23 '19 at 0:32
  • \$\begingroup\$ If two devices are wired in series, the same will flow in both devices. \$\endgroup\$ Nov 23 '19 at 0:44
  • \$\begingroup\$ Would the extra breaker pop as well and protect the devices in a series from possible damage? Thank you for helping me to understand I appreciate it. \$\endgroup\$
    – j w
    Nov 23 '19 at 0:49
  • \$\begingroup\$ Like a gcfi outlet or a similar extender that you plug into an outlet with a circuit breaker \$\endgroup\$
    – j w
    Nov 23 '19 at 0:50

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