Final answer:
Electrical systems incorporate circuit breakers or fuses and a three-wire system to protect against thermal and shock hazards.
Step-by-step explanation:
The two built-in safety mechanisms in electrical systems are circuit breakers (or fuses) and the three-wire system. Circuit breakers and fuses are designed to interrupt excessive currents to avoid thermal hazards, such as electrical fires caused by overheating. The three-wire system consists of live/hot, neutral, and earth/ground wires, with the neutral wire and case of the appliance being grounded to protect against both thermal and shock hazards. This system ensures that any fault current is directed harmlessly into the earth, thereby preventing electric shock to users.