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I often find that consumer electronics from reputable brands come with fused plugs that are rated significantly higher than the actual product.

I would have thought that the ideal fuse would be \$x+\epsilon\$ where \$x\$ is the product's expected maximum draw. Obviously, that's not practical, but frequently I find the fuses are larger than they 'have to be', that there's a standard size between what they shipped and \$x\$.

Is it just being cheap, using whatever's available (even if it's actually more expensive than the better choice, I suppose it may be 'cheaper' by availability)?

Surely the greater difference between the fuse and \$x\$ the less point there is in having it at all. Or is it more complex than I realise, should I prefer whatever was shipped over one closer in rating even if I happen to have it?

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    \$\begingroup\$ The formatting help says inline latex can be achieved with single dollars, but it's not rendering for me? (Double dollars for blacks worked fine so seems unlikely it's just an issue my end, but I'm not certain.) \$\endgroup\$
    – OJFord
    Commented May 30, 2020 at 16:15
  • \$\begingroup\$ \$x\$ is the way to get \$x\$. \$\endgroup\$ Commented May 30, 2020 at 16:16
  • \$\begingroup\$ I just saw in your edit, thanks! This could do with fixing here: electronics.stackexchange.com/editing-help#latex \$\endgroup\$
    – OJFord
    Commented May 30, 2020 at 16:17
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    \$\begingroup\$ @BrianDrummond Republic of Ireland, and I believe some of the Commonwealth. \$\endgroup\$
    – OJFord
    Commented May 30, 2020 at 16:55
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    \$\begingroup\$ @BrianDrummond Malta, Saudi Arabia, Malaysia, Sri Lanka and loads more \$\endgroup\$
    – Finbarr
    Commented May 30, 2020 at 20:38

2 Answers 2

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The purpose of the fuse is not to protect the product, it's to protect the wiring — to keep it from getting hot enough to start a fire. The fuse is rated according to the gauge of the wire. The only connection with the actual power consumption of the product is that the wire gauge must be selected to support the expected power draw.

The same thing is true for the circuit breakers in your house. They exist in order to keep the branch circuit wires from overheating in the walls.

In most jurisdictions, the minimum permitted wire size is established by regulations. For example, in the USA, the minimum gauge for house wiring is AWG14, and the minimum gauge for product line cords is AWG18.

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  • \$\begingroup\$ So my final paragraph in OP was misinformed, but still, there's no reason to use much thicker cable and fuse than necessary for the product, right? So, ceteris paribus, the smaller stuff is cheaper, and the only 'reason' to ship a larger one would be that it happens to be what you have? \$\endgroup\$
    – OJFord
    Commented May 30, 2020 at 16:52
  • \$\begingroup\$ Yes. It's one form of inventory cost reduction for the manufacturer. They come out ahead even if the individual product appears to be more expensive. \$\endgroup\$
    – Dave Tweed
    Commented May 30, 2020 at 17:06
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In addition to the answer by Dave Tweed, while BS1362 fuses can be bought in a wide variety of ratings, there are only two "standard" values that people are expected to keep to hand. These are 3A and 13A. 3A is for small flexes on things such as table lamps. 13A is for everything else. So long as the fuse blows before the flex melts, that is considered acceptable.

In reality a lot of IT equipment is supplied with cables only rated at 6A, so these are often fitted with 5A fuses.

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