Posted By Alec Wood Hi Nigel You are broadly speaking correct. However, they are correct also in that monitors, PC's etc have seperate internal fuses of the correct rating for the appliance. This is because the lead is detachable, and in some countries will not contain any fuse. For this reason it is now common to fuse the appliance itself, and the choice of fuse sizes is much greater than that available at the plug end of things. e.g. A monitor is likely to be fitted with a 1.2 amp fuse. In the case of a short to earth, it makes no difference really if it is 3 or 5 amp, the fault current will be so massive it will rupture just as quickly. The main purpose of a fuse is to protect the conductor from overheating due to excess current drain, and thus to protect the owner from fire. In the case of an appliance which draws 5.1 amps, you would be quite happy to see a 13 amp fuse (as long as the cable was appropriate) even though this is 7.9 amps above the normal load current for the appliance, so why is it a problem if a 5 amp fuse is fitted which is 3.8 amps above the normal load current? I do not see any safety case to use as a stick on Dell in this instance. If you analyse each potential fault condition you will find that they have all the bases covered. I'll agree it would be "better" if they fused at 3 amps, but then it would also be "better" if we had more than three standard fuse ratings for UK plugs available too! Alec Wood Samsung Electronics

Posted By Tim James I have to say that I agree with Dell here. The advice you have been given, ie that a 3A fuse should be used for an appliance up to 700 watts is not bad advice, just a little too basic for someone doing pat testing. In fact, the most important fact here is that the purpose of the plug top fuse is to protect the CABLE, not the appliance. This is a difficult concept to understand, but you must remember that the BS1363 plug is practically the only plug worldwide that contains a fuse. In every other plug you expect to fit an appropriate cable - old style 15A plugs and 16A commando plugs are always fitted with 1.5mm cable for example, round pin 3A plugs used on lighting circuits are always fitted with 0.5mm cable. The BS1363 plug is unusual in that it can be fitted with different cables, and this is why it is fused. Initially, the authorities expected that appliances would be fitted with 0.5mm cable (requiring a 3A fuse in the plug) or 1.25 or 1.5mm (requiring a 13A fuse in the plug.) and this is why BS1362 only initially recognised 3A and 13A values (and why 3A are RED, 13A BROWN and all the other values BLACK) Nowadays, it is very common to find equipment fitted with 0.75mm cable (which is rated nominally at 6A) and so we are required to fit a 5A fuse in the plug. So, you might say, why not fit a 3A fuse, or even a 1A or 2A if the appliance is low power? The answer, in this case lies in the fact that the IEC lead is detachable, and can therefore be used on other appliances. The cable and connector are rated at 6A and we therefore fit a 5A (next lowest) fuse in the plug. Manufacturers expect this, and fit IEC connectors to many appliances, some of which are rated at a higher power. Consequently, if a lead fitted with a 3A fuse were to be used on an appliance which required more current, the fuse would eventually blow. This, as we all know, is when a less knowledgable or less careful user starts to replace the fuse with a 'brown' one or if one is not to hand, something like a bolt or piece of tin foil!!! When we teach pat testing courses, we advise people to start by looking at the power rating of the appliance. From this, it is possible to calulate the current drawn by the appliance. This then enables you to determine whether the cable is thick enough. If so, the fuse in the mains plug should be selected to protect the cable. Standard IEC cables are always fitted with .75mm cables and should therefore be fitted with a 5A fuse. (For completenes I should also point out that there is a version of the IEC connector known as a 'hot condition'which is fitted with 1.0mm cable and therefore fitted with a 10A fuse. This latter type is used on kettles etc) There are other points to raise here, I could go on all night! But I hope this comments are helpful, and you don't fall out with Dell too much. I have to say that we test approx 5000 dell computers every year and they are usually the best built and have the lowest rate of failure of the computers that we test.