# Voltage across voltage source in a short circuit

When we short-circuit a voltage source, the current will be very high. The voltage across the wire is 0V. If we apply KVL, also the voltage across the voltage source is 0V. How can it be 0V if we have a voltage source?

• You absolutely have to always think of a voltage source as an ideal voltage in series with a resistor. A good voltage source has a low value for that resistor, but it is not zero. – DanielSank Feb 7 '16 at 20:40

• Ohm's law isn't the problem. The problem is assuming that the source has zero output resistance. Ohm's law just says $V = IR$. There's nothing approximate about that. OP is making the mistake of putting $R=0$ into that equation. – DanielSank Feb 7 '16 at 21:07