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I have a trouble solving this problem. (Actually, each resistor is not parallel with the bottom wire since the voltage across each of them is different with that of wire.)

In the manual, the bottom wire(which is red circled) is simply ignored and thus can be easily solved.

I don't understand why the bottom wire can be ignored. At first, I thought it's because the node between the wire has the same voltage, making voltage difference across the wire to be 0 resulting current flowing through the wire to be 0.

I used mesh current method by myself, not ignoring the bottom wire and i got different answer, which indicated that the wire has some non-zero current flowing through it.

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  • $\begingroup$ Redraw the circuit so the 7 and 1 ohm resistors are vertical, in series with the 20 ohm, and with their bottom ends connected to each other and to both sources. Then it'll make more sense. $\endgroup$ – hdhondt Apr 24 at 6:07
  • $\begingroup$ If you have trouble understanding what's going on, I suggest you try inserting a resistor with resistance $r$, then analyze the circuit and at the end take the limit where $r\to 0$. $\endgroup$ – Ofek Gillon Apr 24 at 7:02
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    $\begingroup$ What is being asked for in the problem and what do you mean by “ignored “? $\endgroup$ – Bob D Apr 24 at 10:31
  • $\begingroup$ hdhondt answered the question. In the figure the node showing the junction of 7 ohm resistor and -480 V and the node showing junction of 1 ohm resistor and +168 V are in fact THE VERY SAME NODE. $\endgroup$ – K7PEH Apr 24 at 14:39
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Just because a wire forms an equipotential structure does not mean there is no current. Otherwise, current wouldn't flow from the 480 V source + point to the beginning of the 5 $\Omega$ resistor. Don't worry about the non-zero current. Pay attention to the question the problem is asking (which you haven't shared with us).

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