Final answer:
A time delay fuse can handle high initial surges of current above its rated value for short durations, which allows for the startup of devices with high inrush currents like those with electric motors. However, the continuous operating current should not exceed 80% of the fuse's current rating to prevent potential thermal hazards.
Step-by-step explanation:
A time delay fuse can handle brief surges of high current, such as when a device is first turned on and draws a higher current temporarily—a phenomenon known as cold current. These surges can be substantially greater than the steady-state operating current of a device. For example, if a light bulb normally operates at a steady-state current of 2.50 A, it might briefly draw a much higher current when first switched on. However, the current quickly declines as the bulb's temperature stabilizes. Special slow blow fuses are designed to tolerate these high inrush currents for a few seconds, making them suitable for appliances with electric motors that also experience high startup current.
For example, a 15-A fuse on a 120-V circuit would trip if the continuous current exceeds 15 A. However, the safety margin typically allows continuous load to be a maximum of 80% of the fuse's rating, which would be 12 A in this case. To assess whether a combination of household devices will blow the 15-A fuse, we need to calculate the total current drawn by all devices in parallel.
- An 1800-W toaster draws 1800 W / 120 V = 15 A.
- A 1400-W appliance, like a speaker or an electric frying pan, draws 1400 W / 120 V = 11.67 A.
- A 75-W lamp draws 75 W / 120 V = 0.625 A.
Therefore, this combination will certainly blow a 15-A fuse.