Electricity can flow either as direct or alternating current, and is used in homes to power electrical appliances.
Part of Combined ScienceElectricity
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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.