Appliance fuses

[stillp]

ericmark, as suspected, the EU to make things a little more compatible, rather than a sound old fashioned electrical approach.

Not the EU, but CENELEC. Decided by sound old fashioned electrical engineers.

 

[Gerrydelasel]

A household 100W tungsten has a cold resistance of 42 ohms. If you switch it on at the mains peak then you've got 8 amps of instantaneous inrush.

 

[PBC_1966]

And peak inrush currents apply to many things. I have an HP LaserJet printer sitting next to me for which the specification indicates a normal operating current of 7.8A, but with a peak inrush current of 22A, with 18mS 25% decay time (ratings for 120V 60Hz).

 

[ericmark]

I was asked about a charging trolley for laptops. Not sure how many it was to supply a class room so likely 20. Now my laptops power supply says input 2A at 100 ~ 250 volt output 19.5 volt at 4.7 amp. The 2A refers to at 100 volt so at 230 it is more like 0.4 amp. So the trolley likely supplied around 10A to all the chargers, but read the speck and it was around 40 amp.

I was told 2 and 2 makes 4 but it can also make 22!

 

[ban-all-sheds]

On that note, here's an OT "next in the sequence" puzzle

12
1112
3112
132112
............
............
............

 

[securespark]

endecotp, I am beginning to think I do.

Not yet, you don't.

A 13A fuse when the appliances draws around 4A is way over rated.

Not for the appliance flex, which it is designed to protect.

I was reading that they put 13A fuses in because the same appliance will sell in Europe where they have 16A radial circuits and no fuse in the plug.

How are our fellow Europeans in France, Germany, Spain, etcetera going to fit a BS1363 plug into their socket outlet?

A household 100W tungsten has a cold resistance of 42 ohms. If you switch it on at the mains peak then you've got 8 amps of instantaneous inrush.

Now I know why the cat in your avatar is looking mentally stretched! She's trying to work it all out!

 

[WhydidIstart]

On that note, here's an OT "next in the sequence" puzzle

12
1112
3112
132112

1113122112

 

[ban-all-sheds]

That's it.

 

[Mikefromlondon]

Is that it, I hope you got your thingy sorted! (don't say too much here) I hope you didn't have to move the wall instead!

 

[ban-all-sheds]

Is that it,

And then it's 311311222112

I hope you got your thingy sorted! (don't say too much here)

Oh that's long(ish) term.

 

[WhydidIstart]

Back to the topic, I found a 1A mains fuse in a lamp which had blown as the bulb had blown which is a nuisance failure.


However I have also had an appliance become faulty and catch fire = house fire and the 13A fuse did not blow. Interestingly when the fire brigade dragged the unit outside the mains lead was fine I'm not saying a lower, or more closly 'matched' fuse would have prevented the fire, but it may have done.


So a reason to use a lower value fuse where possible may be a potential lower risk of fire, it's just a wiki, but this is corroborated here http://wiki.diyfaq.org.uk/index.php?title=Fuse "Using a lower fuse value where possible can reduce risk of fire."


I have seen a 5kW pool heater tested using a standard 13A plug and operate at over 20 amps for over 10 minutes without blowing the 13A fuse, so it is possible to heavily overload the appliance. Yes a lead in free air may be rated to take this overload, but what if it is under a pile of washing, or someone has stored some insulating materials where the cable runs?

 

[Iggifer]

However I have also had an appliance become faulty and catch fire = house fire and the 13A fuse did not blow. Interestingly when the fire brigade dragged the unit outside the mains lead was fine I'm not saying a lower, or more closly 'matched' fuse would have prevented the fire, but it may have done.

Sorry to hear that, however, the manufacturer of said item - you don't say what it was, should have done a better job of designing/protecting their product. Also, a fuse is not a 'catch-all' for every electrical fault that can occur.

 

[Mikefromlondon]

Back to the topic, I found a 1A mains fuse in a lamp which had blown as the bulb had blown which is a nuisance failure.


However I have also had an appliance become faulty and catch fire = house fire and the 13A fuse did not blow. Interestingly when the fire brigade dragged the unit outside the mains lead was fine I'm not saying a lower, or more closly 'matched' fuse would have prevented the fire, but it may have done.


So a reason to use a lower value fuse where possible may be a potential lower risk of fire, it's just a wiki, but this is corroborated here http://wiki.diyfaq.org.uk/index.php?title=Fuse "Using a lower fuse value where possible can reduce risk of fire."


I have seen a 5kW pool heater tested using a standard 13A plug and operate at over 20 amps for over 10 minutes without blowing the 13A fuse, so it is possible to heavily overload the appliance. Yes a lead in free air may be rated to take this overload, but what if it is under a pile of washing, or someone has stored some insulating materials where the cable runs?

I will go some way agreeing with your logic, yes indeed I also install slightly underrated fuses in the hope they blow out before they have a chance to burn anything else. But for a washing machine, if you measured your s drawing 4 amps, that is most likely not running on full load, or its heater not on, you may have been testing its full load current on its highest spin minus any clothes, in which case if you installed a lower rated fuse, it may eventually blow out on fully loaded machine when it is on its highest spin cycle, which can last a few minutes, if your underrated fuse blows out and your mains socket is behind the machine, it means pulling out the machine just to replace a fuse. In some things like table lamps, yes you could do that.

In a similar scenario with a team of fire officers advising people how important it is to install Fire Detectors, and that we should also fit one in the kitchen where most fires break out when people leave pots and pans on the cooker and forget about them, so I said I have done many times and my smoke detector in the hall way fires up and alerts me to a potential melt down, and I explained to them that why many people don't fit one in their kitchen is because of the smoke triggering the smoke detector, so the guy said you can fit a heat detector, but has anyone given it a thought what exactly is a heat detector?

So I argued that heat detectors would be pointless as they only work on after a fire has broken out. Apart from saving your life it does not save your property.
A smoke detector does both, though it may become nuisance in a kitchen, better safe than sorry!

yup so i would say (that is just my opinion as well, that by fitting a smaller value fuse, it may protect an item just as well, but could cause nuisance by blowing up on prematurely or with intermittent load excursions and get tired in a long run, but equally well remember that a lower value fuse drawing current to near its max rating can cause fire by glowing up red, or before blowing outright, and that the heat it generates when glowing red hot can damage the plugs, I have rarely seen any plugs going up in flames, though one cannot rule this possibility.

so like you said to protect an item that needs 4 amps, one can safely fit a fuse rated slightly higher but one should not fit a 4 amp for a 4 amp load, danger of overheating. So my choice would be to fit a 5A for a 4 amp load rather than a 13 amp from the standard stock.

 

[SimonH2]

Not always easy to prevent single phasing when a fuse blows, ...

I recall my dad telling me of a job he got called out to back when he was a jobbing lecky. This particular one was to a joinery workshop, and they couldn't make one machine work - it just wouldn't start.
It turned out that they'd lost a phase on the supply, and they must have either already had stuff running, or had enough stuff running for the smaller machines to start with the synthetic 3rd phase the 3 phase machines were creating. But this one machine wouldn't start without the real 3rd phase.

 

[WhydidIstart]

Iggifer - Thanks, nobody hurt just property damage which is the main thing. I completely agree, the fire should not have happened in the first place - but things do happen and bad design or double or triple faults do occur sometimes. It was a tumble dryer. I always emptied the lint filter on every use, but something went wrong and it caught fire.


Mikefromlondon - I'm not the 4amp washing machine guy! Mine have 13A fuses and ~2kW heaters inside and no, I haven’t changed them from 13A to 10A even though they may still operate with a 10A fuse.


Even after the fire, I didn't go round changing all my appliance fuses. However in the days of "fake" plugs and dangerous equipment with fake CE markings, etc making its way into the market, I would err on the side of caution and use lower than 13A fuse ratings where appropriate rather than the recent "3 or 13A" guide, if I happened to be replacing a damaged plug for example.


See http://www.bs1363.org.uk/ for fake plugs.


I think a reasonable summary of the points so far are:

• It is generally safe to use the manufacturer's stated fuse size.
  
• Reducing the fuse size [edit: to an appropriate level, but still in excess of the appliance’s normal consumption] may cause nuisance failure of the fuse in some appliances, however it may also provide better, albeit not deemed necessary by the manufacturer, protection against some fault conditions that result in prolonged overloads but not dead shorts.