Wikipedia:Reference desk/Archives/Computing/2019 May 24

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May 24

What should be the fuse rating for 1500W 250V AC 4 socket single switch spike guard /spike buster

What should be the fuse rating for 1500W 250V AC 4 socket single switch spike guard /spike buster/spike suppressor/power strip with spike suppression/surge protection ability that will be used for desktop computer LED/LCD monitor.122.15.54.25 (talk) 10:36, 24 May 2019 (UTC)

Look on the back of the power strip, packaging or similar. That is the only definitive answer. At a guess since 1500W => 6A you'll need a 13A fuse, a 5A one won't quite cut the mustard, but please check the equipment first. Martin of Sheffield (talk) 10:45, 24 May 2019 (UTC)

You should talk to an electrician. The question is posed a bit backwards. The fuse rating should be whichever fuse rating is safe for your building without causing a fire; and then, the follow-on question would be, given this maximum safe fuse rating, can I reliably plug in this computer and monitor without blowing the fuse?

Because this can affect fire-safety, you should definitely consult a professional. If you put a bigger fuse than safe, the computer may stay on and the fuse may operate correctly, but the wiring might overheat and the building might burn down.

This is the top cause of electrical fire in most parts of the world. According to the 2018 Home Fires Report published by NFPA, electrical distribution - including wrongly-set fuses - were the #1 most significant contributor to dollar-losses, and the #3 cause of deaths, in home fires in the USA. This stuff is easily preventable: don't overload your wires! If you're blowing fuses, ask an electrician!

Nimur (talk) 17:16, 25 May 2019 (UTC)

You don't say whether this is the fuse for the 13A plug attached to the power strip, or the fuse protecting the wiring from the distribution board. As Martin says above, six amps would be sufficient, but such fuses are rare. I used to have some ten amp fuses, but thirteen amps is now standard for a 13A plug in the UK. However, this assumes that the flex to the power strip is rated at 13 amps. As mentioned above, if you are blowing fuses, then consult an electrician. Dbfirs 20:43, 25 May 2019 (UTC)

• This is presumably India. It's not clear what fuse ratings are available to you. A 10A would be common British practice, or a 13A as the most usual.

The point is, what is the fuse for? It's not there to protect against overloads (i.e. plugging an 1800W load into this strip rated at 1500W). This type of plugtop fuse is a fairly crude device - it's just not reliable to protect against such misuse, you also have to check manually that you simply haven't plugged in more than that load. That is why extension leads are an insidious risk for fires when overloaded - you can't expect them to detect overloads like that.

The purpose of the fuse supplying the extension lead is primarily to protect against faults, rather than overloads, such as shutting the cable in a door and damaging it. That will (usually) be protected by a 13A fuse. Equally, each piece of equipment is protected by a fuse in its own plug, and these can be low-rated, often 1A or 3A. As these also only carry the load of a single equipment, and their fault currents are probably as great as a fault in the whole strip, that ratio is greater, thus easier to protect with a fuse. If it's important to equipment to protect at a lower current, there will be a fuse on the back panel of the equipment, rather than in the plugtop. This fuse will be a 20mm "electronics grade" fuse, rather than a "plugtop" ceramic fuse and they can have much lower and more precise ratings. Those are where overload protection is done, if needed.

What would I fit? Well I'd fit a 3A (maybe 5A) fuse and I'd lower the usable rating of the extension strip (I'd also label it, for future replacement). If this is a surge protection strip for a computer and monitor, then I don't need 1500W of load, even if the strip can handle that. My computer load might be more like 300W (and a 3A fuse is plenty). I don't want anyone to plug in an electric heater or big motor load into this 'clean' strip, alongside my computer. Andy Dingley (talk) 17:41, 26 May 2019 (UTC)

Surely the purpose of a fuse is to protect the infrastructure downstream of the fuse. Imagine that a big fat cable enters your house, capable of supplying 100A without problem. You don't want to wire evry single thing in your house with 100A capable wire, so you fit a 13A fuse and then can use smaller 13A wire.. Then perhaps you want to use 5A wire which would overheat if used at 13A, so you have to fit a 5A fuse where the 5A wire starts. Then maybe within a unit it is wired with 1A wire. Thus it needs a 1A fuse - strictly it needs higher rated wiring from the inlet to the unit to the fuse than it has after the fuse. You never want a wire to carry more current than it is rated for. Also cable ratings change depending upon whether they are alone in free air, tightly enclosed or bundled with other wires. So 5A wire is only 5A rated sometimes - in a bundle maybe a 3A fuse would be appropriate. -- SGBailey (talk) 11:16, 29 May 2019 (UTC)

SGBailey Exactly. Andy Dingley Re "insidious risk". It is interesting that throughout the 1960s, 1970s, 1980s and 1990s the fire service regularly railed against people building "christmas trees" and advised people to fit extra sockeets to avoid this practice. Since Prestcott's changes to the building regs it is noticeable how many sockets have extension strips more or less permanently attached. Forty years of campaigning by professionals overturned by a cabin steward's attempt to placate unions. :-( Martin of Sheffield (talk) 12:52, 29 May 2019 (UTC)

The proliferation of low-power electronic devices has rendered 40-year-old thinking about building power receptacles obsolete. In today's environment, if you want each device to plug directly into a building power receptacle, and allow for the reality that people will use their devices based on where the furniture is rather than where the receptacles are, you would need to provide a continuous strip of receptacles all the way around every room, spaced about 50 mm apart. All of them would have to be surge-protected. I am not aware of any proposals by the "professionals" to do that. If they professionals don't make realistic proposals they will be, and are being, ignored. Jc3s5h (talk) 17:06, 29 May 2019 (UTC)

That's about the socket spacing I have. Where the computers are in the study, there's a line of C13 outlets. There's also a wall-mount USB outlet with 8 outlets in the space of a single socket outlet. The server rack has another PDU on it, with C13s and BS1363s. Andy Dingley (talk) 17:47, 29 May 2019 (UTC)

You don't need surge protection for the vacuum cleaner, lamps, TVs, reclining chairs, stereos or anything in either the kitchen or workshop. The latter two are where the use of strips is particularly bad and where the fire brigades were most insistent about adding rows of sockets. Martin of Sheffield (talk) 19:37, 29 May 2019 (UTC)