Electricity can flow either as direct or alternating current, and is used in homes to power electrical appliances.
Part of Combined ScienceElectricity
Fuses come in various ratings, but the common sizes are 3 A, 5 A and 13 A.
The current flowing through an appliance can be calculated using the equation:
Electric power P = voltage V x current I
P = VI
Once the current is known the next highest fuse rating is chosen.
Example
A toaster has a power rating of 750 W, 230 V.
P = 750 W
V = 230 V
750 W = 230 V x I
I = \(\frac{\text{750 W}}{\text{230 V}}\)
I = 3.26 A
The normal current for the toaster is 3.26 A. Hence a 5 A fuse would be selected.
A 3 A fuse would 鈥渂low鈥 when the normal operating current flowed.
A 13 A fuse would allow dangerously high current to flow and still not blow.
A bed side lamp is rated 60 W, 240 V.
Calculate the size of fuse that should be fitted to the lamp for it to operate safely.
The fuse available are 3 A, 5 A and 13 A.
P = 60 W
V = 240 V
60 W = 240 V x I
I = \(\frac{\text{60 W}}{\text{240 V}}\)
I = 0.25 A
The normal current for the lamp is 0.25 A. Hence a 3 A fuse would be selected.