Step 1: What is shunting?
Shunting an ammeter involves connecting a low resistance in parallel with the ammeter to allow most of the current to bypass the meter. This prevents the ammeter from being damaged by high currents.
Step 2: Effect on the measurement limit.
When the ammeter is shunted, its range of measurement is increased, meaning it can measure higher currents than it could without the shunt. The shunt bypasses most of the current, allowing a small current to pass through the meter and increasing its range.
Step 3: Conclusion.
Thus, when an ammeter is shunted, its measurement limit increases.
\[
\boxed{\text{Correct Answer: Increases}}
\]