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I have a small portable fan that, for reasons beyond my understanding, has a fuse inside of the plug. The fan stopped working because the fuse broke. At the store, I couldn’t find a fuse nearly as tiny as the one in the plug, but a colleague suggested I look in my Christmas lights because they often have the same size fuse in those plugs. Surely enough, I found the size fuse as a spare in a box of unused Christmas lights. The only difference is the fuse is labeled as 3 amps, and the plug of the fan has this text on it: Plug

So, I’m just curious what danger lies in using a 3 amp fuse here. Could the fan be damaged? Could the house burn down? Something else?

  • You said the fuse broke. Like snapped in two? Or do you mean it blew? Why would it blow? – Harper - Reinstate Monica Feb 1 at 22:02
  • @Harper-ReinstateMonica - I hadn’t used it in a few months and when I tried to, it didn’t turn on. I opened that fuse cover to discover it was broken in two. I suppose maybe after being unplugged, it could have dropped on the floor hard enough to break the fuse. – bubbleking Feb 2 at 2:53
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    you could almost surely use a 2A fuse, unless you have one heck of a fan. – dandavis Feb 2 at 3:23
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    @dandavis that's a good notion. Sounds like an answer to me. 240 watts is an awful lot for a fan. OP since it physically cracked you don't have to worry about the fan being defective and having burned out the last fuse. – Harper - Reinstate Monica Feb 2 at 6:40
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    I don't think you could argue that replacing a 2.5 amp fuse with a 3 amp one was negligent. – Jack Vand Feb 2 at 8:05
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Disclaimer: I am a visitor here from Electrical Engineering SE. Exceeding recommended safety ratings always comes with some amount of risk. Whether that risk is significant can vary greatly depending on the particular situation. Take the following answer with the greatest of precaution.

I don't think the difference would cause any significant issue, as any hard failure would blow the 3 Amp fuse just as fast as it would a 2.5 Amp fuse, for most practical purposes.

In higher powered or more critical situations, one would be wise to be very careful about safety concerns. In this situation, 3 Amps of current would not likely even come close to pushing the limits of the branch circuit to which the item is connected before the 3 Amp fuse blows.

If the offset in ratings between the two different valued fuses were larger, then there might be some room for concern, but one has to consider that fuses are not an exact science. In their simplest form, their tolerances can vary greatly.

According to the manufacturer "Littelfuse" on page 4 section 1 in this PDF, just a change in temperature alone can change the rating of the fuse by 25%. Furthermore, section 3 on the same page actually shows a situation where a circuit that is intended to blow a fuse at 2.25 Amps, actually should use a 3 Amp fuse.

  1. NORMAL OPERATING CURRENT: The current rating of a fuse is typically derated 25% for operation at 25ºC to avoid nuisance blowing.

In view of this, the 2.5 Amp specification being 16% less than the 3 Amp fuse you would like to use seems insignificant. Based upon the above-linked PDF, the original 2.5 Amp fuse could have passed over 3 Amps of current before it blew if the fuse were very cold.

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Fuse selection at a local hardware store is often limited to the types that are likely to be used by customers in the area. You should instead consider looking at a distributor that you can access online to gain access to a much larger selection.

If I am not mistaken you are looking for a micro fuse that measures 3.6x10mm in size. You can find sets of fuses rated at 2.5A 125V or even 250V.

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Picture Source

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  • Thanks, that’s very helpful. Just curious if you happen to know why a simple desk fan would have a fuse in its plug? – bubbleking Feb 1 at 17:01
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    @bubbleking - It is hard to say why there would be a fuse in the plug. Some possible thinking may be: (1) Fuses in plugs are common in the UK. (2) Maybe the fan can severely overheat if the fan blade is blocked for some reason and the stalled motor draws enough current to blow the fuse. (3) Possibly the power cord can become frayed to the extent that the wires in the cord can short out which would pop the fuse as a safety measure. – Michael Karas Feb 1 at 17:08
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    @bubbleking Probably because UL put a gun to their head and said "you can either put a fuse on it, or totally redesign the fan to meet UL standards without a fuse". And the fuse cost less. – Harper - Reinstate Monica Feb 1 at 22:04
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You are taking the risk that your house could burn down, and that your insurance policy could be void because you knowingly caused the fire.

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    I would change "knowingly" to "negligently". – stevieb Feb 1 at 20:26
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    Even though it should be painfully obvious, it wouldn't hurt to include how the fire might start: e.g., if a 2.9A current flows for an extended period of time, it could -while not strong enough to trigger the 3A fuse- melt the 2.5A rated-plug uncapable of dissipating the excess heat caused by the increased electrical resistance arising from that 0.4A of extra current. – Will Feb 2 at 1:23
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    @Will - do you really believe plugs etc. are made to that close a tolerance? – Tim Feb 2 at 9:42
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    After the house has burnt down, there would be a little lump of metal that was once a fuse. It's highly unlikely that would happen anyway, but how could anyone prove it was once a 3A fuse? – Tim Feb 2 at 9:45
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    @Tim It seems unlikely, but I don't know how else said house is supposed to burn down? I'm just spelling out the prerequisites required for Phil's answer to be at all realistic. If it isn't, then this answer amounts to little more than fear-mongering. – Will Feb 2 at 10:56

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