          # Fuse Rating

This web page explains fuse ratings.

This web page answers the questions:

• What are typical fuse ratings?
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• How to calculate the fuse rating.
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• What is a fuse rating?
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• Why are fuses rated?

## Typical Fuse Ratings

• Clock radio – 3 amp.
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• Coffee maker – 5 amp.
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• Dishwasher – 13 amp.
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• DVD player – 3 amp.
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• Electric blanket – 3 amp.
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• Fan – 3 amp.
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• Food mixer – 3 amp.
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• Fridge – 3 amp.
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• Hair dryer – 13 amp.
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• Hi-fi – 5 amp.
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• Iron – 13 amp.
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• Kettle – 13 amp.
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• Lamp – 3 amp.
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• Laptop PC – 3 amp.
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• Microwave oven – 5 amp.
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• PC – 3 amp.
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• Table lamp – 3 amp.
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• Toaster – 5 amp.
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• TV – 3 amp.
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• Vacuum cleaner – 3 amp.
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• Video player – 3 amp.
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• Washing machine – 5 amp.

## How To Calculate The Fuse Rating

Using the guideline that the fuse is rated at 125% of the normal operating current.

Power (Watts) = Current (Amps) x Voltage (Volts)

Therefore:

Current = Power/Voltage

Therefore:

Fuse rating = (Power/Voltage) x 125%

OR, put another way:

Fuse rating = (Power/Voltage) x 1.25

OR, put another way:

Fuse rating = (watts/volts) x 1.25

• Note the power of the appliance – usually in the appliance manual,
• Note the voltage (240 volts in the UK).
• Use the next highest fuse rating after the calculation.
• Say the calculated fuse rating is 2.2679 amps, use a 3 amp fuse.
• Say the calculated fuse rating is 4.9431 amps, use a 5 amp fuse.
• Say the calculated fuse rating is 8.9032 amps, use a 13 amp fuse.
• Say the calculated fuse rating is 10.6421 amps, use a 13 amp fuse.

### Fuse Rating Calculations

The assumption in this calculation is that their are only 3 fuse ratings, 3 amp, 5 amp and 13 amp.

Say the power is 500 watts.

Fuse rating = (watts/volts) x 1.25

Fuse rating = (500/240) x 1.25

Fuse rating = (2.083333333) x 1.25

Fuse rating = 2.604166667 amps

Next fuse up is a 3 amp fuse, use a 3 amp fuse.

Say the power is 200 watts.

Fuse rating = (watts/volts) x 1.25

Fuse rating = (200/240) x 1.25

Fuse rating = (0.83333333) x 1.25

Fuse rating = 1.04166667 amps

Next fuse up is a 3 amp fuse, use a 3 amp fuse.

Say the power is 1500 watts.

Fuse rating = (watts/volts) x 1.25

Fuse rating = (1500/240) x 1.25

Fuse rating = (6.25) x 1.25

Fuse rating = 7.8136 amps

Next fuse up is a 13 amp fuse, use a 13 amp fuse.

Say the power is 900 watts.

Fuse rating = (watts/volts) x 1.25

Fuse rating = (900/240) x 1.25

Fuse rating = (3.755) x 1.25

Fuse rating = 4.6875 amps

Next fuse up is a 5 amp fuse, use a 5 amp fuse.

## What Is A Fuse Rating?

A fuse rating is the current need to blow (break) the fuse.

When a fuse has blown it removes electrical power from an electrical circuit.

The fuse rating is usually on the side of the fuse.

The fuse rating is usually defined in ‘amps’ – amps are the unit of measurement of electrical current.
Miles are a unit of measurement of distance, Celsius are a unit of measurement of temperature, amps are the unit of measurement of electrical current. ## Why Are Fuses Rated?

Fuses have different ratings so they can protect different electrical circuits.

Different electrical circuits use different amounts of electrical current – what may be too much electrical current for one electrical circuit may not be too much for a different electrical circuit.

A fuse that blows at, say, 10 amps is no use in an electrical circuit that uses 12 amps – the fuse would blow during normal circuit working.

A fuse that blows at 10 amps is no use in an electrical circuit that is using too much electrical current at 5 amps. The electrical circuit would be using double the ‘safe to use’ electrical current before the fuse blows.