Final answer:
A fuse or a circuit breaker is used to prevent excessive current from passing through a circuit, protecting against thermal hazards. GFIs and isolation transformers provide further safety from electric shocks.
Step-by-step explanation:
The specified special device that prevents excessive current from passing through a circuit is typically a fuse or a circuit breaker. A fuse is comprised of a wire with a low melting point that melts when excessive current flows, breaking the circuit and preventing further current flow. Fuses need replacement once activated. Circuit breakers, on the other hand, are like automatic switches that trip and open the circuit when they detect a current overload; they can be reset after tripping. Ground Fault Interrupters (GFIs) and isolation transformers are additional safety devices that prevent electrical shock by breaking the circuit when current flows along an unintended path or by isolating the appliance from the source to prevent a complete circuit that could shock a user.
An ammeter measures current and is placed in series within the circuit branch but is not a device meant to protect against excessive current flow.