Final answer:
NC contacts in a magnetic overload device are connected in series with the main circuit to break the flow of current during overload, while household appliances are connected in parallel to maintain the same voltage level for proper operation.
Step-by-step explanation:
The NC (normally closed) contacts in a magnetic overload device are typically connected in series with the main circuit. This design ensures that when the overload device is activated due to an overload condition, the NC contacts open and break the circuit, stopping the flow of current and thus protecting the motor or other components in the circuit. In the context of household wiring, appliances are typically connected in parallel to ensure they each receive the same voltage level, which is essential for their proper operation.