Final answer:
Connecting an ammeter into a powered circuit can blow the fuse or battery in the meter or otherwise damage the meter.
Step-by-step explanation:
Connecting an ammeter into a powered circuit can blow the fuse or battery in the meter or otherwise damage the meter. Ammeters need to have a very low resistance to measure current accurately, and if they are connected in a circuit where the resistance is not negligible, it can change the equivalent resistance and modify the current being measured. To protect the ammeter from damage, it typically contains a fuse to handle high currents.