It’s easy to get confused when checking the plug fuse during PAT Testing.
One important thing to remember is that the job of the person doing the PAT Testing is expected to look at the plug fuse and make a decision on whether or not it is suitable. Many people simply check the fuse and write down the value, without actually considering whether it is appropriate or not!
A very simple way of checking the fuse is to look at the Power Rating on the rating plate of the appliance. You should always be able to see how much power (in Watts) the appliance will consume when in use. A mark of 150W means that the appliance is ‘rated’ at 150 Watts – or to express it scientifically, it will use 150 Joules of energy every second.
If the appliance is rated at less that 700W then the best fuse to use is a 3A.
If the appliance is rated at more than 700W then it can be fitted with a 13A fuse.
This method is very simple, and quite basic, but works well enough.
The main purpose of the plug fuse is to protect the cable, and you may find appliances with 6A cable fitted with 5A plug fuses. This is quite acceptable. Many power tools (such as electric drills and jigsaws) are like this, as well as many mains leads supplied with computers.
It is not usually necessary to replace a small fuse with a bigger one, – for example if a TV is fitted with a 3A fuse, and is working correctly, it would not be a good idea to fit a larger fuse – even if it is fitted with heavier cable. New appliances (provided they are purchased from a reputable supplier) are required by law to have a suitable plug (with an appropriate fuse inside) fitted when sold. However, very old appliances were probably not supplied with a plug, and the person fitting the plug all those years ago has probably fitted a 13A fuse when a smaller one would have been better. Hence, the older the appliance is, the more likely it is that the fuse will be too big.
Be prepared to replace lots of 13A fuses with smaller ones if you routinely deal with older appliances!