The table below will give you the costing in £ & p for operating an appliance for a given length of time. It will also show you the amount of load in amps, required to operate that appliance correctly. You will now be able to make sure the the correct protection fuse it fitted in the plug top, or if it is an electrical circuit, at the consumer unit ( fuse board ).

Step 1/.  Complete the table below by entering the wattage of your appliance, or tungsten light bulb, the time it's going to be used and cost of your electricity per unit into the the correct boxes below.  Now Press the "Calculate Button".
Please enter the full load of the appliance in watts only not KW. ( 1 KW = 1000 watts ).	The Wattage of the Appliances
Please enter the time in hours and minutes that this appliance is to going to be used for   Hours	Minutes
Please enter the unit cost of your own electricity. The amount entered is an estimated price per unit of electricity only.	Pence Per Unit
Please enter the full nominal voltage of the appliance. This is the voltage that is stated on the lamp or appliance.	The Voltage of the Appliance
The table shown below shows the cost of how much the appliance cost to use over a length of time.
Cost per day	£
Cost per week	£
Cost per quarter	£
Cost per year	£
The total load in amps required to operate your appliance correctly is given below. Your appliance requires the nearest larger size fuse or breaker. Fore example a 9.6KW shower requires 40 amps to operate therefore the correct size fuse must be 45 amp in size. The cable size must also be the correct size.
This is the total operating load of the appliance in Amps. The appliance load in amps must be lower than the circuit protection fuse or breaker size in amps. The circuit protection fuse or breaker must in turn be the weakest link of the circuit.This means that the cables, isolating switch and all parts of the circuit must be rated higher than the protection device. If in doubt please consult a qualified electrician.	Load in Amps
The table below give the most common sizes of fuse wire, cartridge fuses and mcb breakers.

Fuse Wire	5 Amp	10 Amp	15 Amp	20 Amp	30 Amp
Cartridge Fuse	6 Amp	10 Amp	15 Amp	20 Amp	32 Amp	35 Amp	40 Amp	45 Amp
MCB Breakers	6 Amp	10 Amp	15 Amp	20 Amp	32 Amp	35 Amp	40 Amp	45 Amp	50 Amp
Guide to Cable Sizes	1.0mm	1.5mm	1.5mm /2.5mm	2.5mm	6.0mm	6.0mm	6.0mm /10mm	6mm /10mm	10mm /16mm

As an Example lets see the difference between a 7.2KW shower replaced by a new 9.6KW shower :

The load of the 7.2KW shower would be    =    ( 7.2KW  x  1000 )    =    7200Watts.      Therefore the load current in amps would be    =    7200Watts    ÷    240volts    =    30 amps.
This means that the fuse size for this shower could be 30 amps, but for more reliability a 35 amp fuse. The alternative is a 32 amp breaker.

Now lets use the same formula to calculation the fuse size required for the new 9.6KW shower.

The load of the 9.6KW shower would be    =    ( 9.6KW  x  1000 )    =    9600Watts.      Therefore the load current in amps would be    =    9600Watts    ÷    240volts    =    40 amps.
This means that the fuse size for this shower could be 40 amps, but for more reliability a 45 amp fuse or breaker.

From the example above, by increasing the shower rating, you increase the load in amps. This means that the protection device must also be increase accordingly. But now is the cable the correct size to carry the additional load?

The table above give a guide to the cable size required for the load in amps. But there are other cable de rating factors that may effect the cable size like length of the cable, the method of the cable installation, loft insulation on top of the cable, etc.

Important Note

All installations or any alteration of an electrical installation must comply with the IEE Regulations currently in force at the time of that installation. You are responsible for what you do by law. Therefore you should not do any think that you are not qualified to do. But consult a professional qualified electrician who will advice you accordingly.

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