Check Your Fuses

  €dstowe 08:17 10 Aug 06

There is a thread running at the moment that mentions that the power lead to a computer had a 13 Amp fuse.

There are NO circumstances where a personal computer or normal ancillary equipment requires to have such a high rated fuse.

Can I suggest that you check the fuses in your power leads for all your computer equipment and, if incorrect, change to something more suitable.

Remember that fuses are protective devices and must be rated at a level suitable for the equipment they are attached to. Most "kettle" type leads are supplied with a standard 13 Amp fuse to accommodate the device they were originally intended for - a kettle which needs the high power rating - your computer does not.

Check soon and if it's wrong, change it. Even the most powerful personal computer should be adequately protected by a 5 Amp fuse. A 3 Amp should be OK for everything else on your computer (printers, scanners, modems and such like).

  The Old Mod 09:35 10 Aug 06

Hi, can I just add, that the primary purpose of a fuse in a domestic plug is there to protect the cable that is attached to it. Each cable has a current rating, therefore the fuse in the plug has to be smaller (current wise) to be able to blow if a fault occurs before the cable overheats or melts and causes a fire.

  €dstowe 14:54 10 Aug 06

Moving up before it drops off the front page.

  VCR97 21:05 10 Aug 06


  Wilham 21:56 10 Aug 06

Advanced electronic design may bring about 13amp plug fuses to psu's, if it hasn't done so already.

Switched mode power supplies (SMPS) have steadily improved in performance over the years. The present ATX ps's basically input the mains to a full wave rectifier which charges a largish capacitor. The potential would reach over 300v but an oscillator loads the source, generating a deformed sine wave 30 to 40kHz. This is fed to a transformer via a 'chopper'.

It has two huge advantages over ancient systems. Firstly it saves weight. An old rule of thumb for mains (50Hz) transformers was 25W/lb. Raise the frequency to 40kHz and there is (my guess) 40-fold power/wt gain Secondly, trains of pulses from the transformer can be switched through to the output, the control is applied at the crossover points when the voltage is zero. This is v nearly 100% conversion efficency.

"OK," you say, "...why 13 amp fuse?"

Answer: Speed of start-up.

I also notice circuit improvements in safety. When SMPS does fail it sets off a domino effect, causing tiny diodes and tenth-watt resistances to burn out, the combination producing what is called 'crowbar protection', and presents a dead short across the mains and blows the fuse,..of whatever amps.

  Wilham 22:34 10 Aug 06

"... at the crossover points when the voltage is zero." should be "... at the crossover points, ie when the voltage is zero."

The name VCR97 strikes a chord. In 1947 I was ill overseas in the RAF and had to wait an extra year to return to university. I spent 1st part of 1948 making a TV from war surplus. The screen was a British VCR97, (Valve Cathode Ray 97). I remember I changed later to an American 5CP1. My bedroom filled up with wires everywhere. Few had seen tv and my folks were glued to the tiny green screen.

Ah well...

  woodchip 22:39 10 Aug 06

Just as important in not more so is check TV's and all Electronic Equipment. That you have the right Fuse fitted, If not this can cause a fire

  squillary 03:26 11 Aug 06

My dad was an Electrical Engineer for 20 years (Marconi) before he went into teaching. He knew all the technical stuff but he liked to get his message across too and not waste time.

When he taught me he said a fuse is there to protect the device. In this case he'd say that using a fuse rated too high was effectively using your computer to protect your plug.

I never needed to ask another question after that.

  GRFT 12:06 11 Aug 06

As already mentioned, the 13A fuse in the plug is to protect the cable, not the connected device, which should have a suitable internal fuse fitted by the makers. In ATX PSUs this is 5 amp.
The UK is one of the very few, if not the only, country that fits fuses to the plugs of domestic appliances.

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