Light keeps blowing a fuse

amandstu

Only twice but I get the feeling that if I replace the fuse again (a 16A round fuse which is probably very old fashioned -you put it in the fuse socket and screw it tight with a round ceramic and metal head) it will go again.

I am surprised that a simple light would be causing a fuse to go (there is nothing else on the circuit- just a couple of wall sockets that are hardly ever used)

16A seems quite sufficient to me for a bedside light.Could I go higher or is that risky?

Lewis_Benson

A light blowing a 16A fuse means something is very wrong. I'd get an electrician to look at that.

amandstu

https://www.boards.ie/discussion/comment/122972708#Comment_122972708

Thanks very much. I will do that.

Lewis_Benson

And don't use the light until you get someone to take a look at that.

Slightly Kwackers

https://www.boards.ie/discussion/2058384984/light-keeps-blowing-a-fuse

Are you serious?

The light plugs into the wall socket I gather?

If it's hardwired into a spur or something and the fault isn't obvious, unscrew it and dump it.

If it has an unfused plug, look for a problem or find someone with a PAT unit

If it has a fused plug, do the same and remove the chunk of metal shorting the fuse link out.

You are using a standard off the shelf lamp I assume and not a carbon arc light or a bulb you got from a chum on the council that get nice orange ones :-)

fritzelly

Buy a new lamp

rob w

You don't need an electrician to look the this . It's sounds like a faulty lamp. Just chuck it and get a new one.

Slightly Kwackers

https://www.boards.ie/discussion/comment/122983552#Comment_122983552

I think blowing a 16A fuse needs a tad more consideration than just a like for like swap.

A typical lamp will have 0.75 or 1mm conductors.

Now why would a 16A fuse pop when the cable will make a perfectly good fuse and provide a far better indication than that of the ceramic fuse as it will give a visible indication using smoke, flame and can even give a more positive indication using the fire brigades engines.

Who can argue that a couple of fire engines pumping water into your house are not more visible than the disk at the rear of the fuse?

The problem does not seem that difficult, but something is seriously amiss somewhere if a bedside lamp causes a power dissipation of 3.7kW in the protected circuit. That equates to a lot of energy if the fuse is a bit lethargic.

If the OP does not know why the fuse has ruptured, he needs to find out rapidly.

rob w

The lamp likely has a short circuit in its wiring. When plugged in, high current flows on the circuit, rupturing the fuse.

A cable is not 'a perfectly good fuse'. A fuse is a fuse. Not sure what you are getting at there!

OP, is the fuse blowing straight away when it gets plugged in?

amandstu

https://www.boards.ie/discussion/comment/122984534#Comment_122984534

No ,not straight away.

It went about a week after I changed the fuse which I thought was suspicious (and likely to recur)

. There is really only that light which connects to that fuse.

It was the first time in 20 years that a fuse has gone so quickly.

I did open up the light but it looks in good shape. Perhaps I should check the plug at the wall.

It is 3 pronged but I can only see 2 wires at the light itself.

I haven't used the light since -just use the main overhead light until I work this through.

Slightly Kwackers

https://www.boards.ie/discussion/comment/122984534#Comment_122984534

Of course a cable is a "perfectly good fuse"

It has Ohm's, not a lot hopefully, but all you need for a fuse is resistance, current and the ability to change from a solid to something else.

I have used glass as a fuse, not to intentionally protect anything I might add, but just to observe the result.

There are those that will argue that glass, or indeed a cable cannot be fuses, but if you stick a whisker of wire wool into a Wylex fuse carrier and feed it from a 30A ring, you still have two fuses. Three if the cable in between is so thin it melts.

A fuse never blows straight away. It might seem to, but if you look at the wiring regulations they provide the response times for fuses and breakers. Manufacturers give curves and go into some detail for rewire-able fuses

Basically this fuse business is common sense and relies on ensuring that the replaceable or other protective device is the weakest link in the feed. Now a 16A fuse is perfectly good no doubt to protect what feeds it, but a bedside light is not normally fitted with a cable that will pass 16A, if that's the case, then the cable should be fed from a smaller fuse, 3A if it's got a BS 1363/A plug.

This prevents the 16A fuse blowing, the cable acting as a fuse and the arrival of the fire brigade :-)

rob w

https://www.boards.ie/discussion/comment/122985109#Comment_122985109

Getting off topic here, but this is waffle. The purpose of a fuse is to safely break an overload or fault current. In a domestic setting or otherwise, nothing else is used for that purpose except for fuses/circuit breakers. Just because a cable could melt and break a circuit doesnt make it a good fuse, I'm not sure I've ever heard an argument like that one before!

rob w

https://www.boards.ie/discussion/comment/122985104#Comment_122985104

Ok, may not be a faulty lamp so. You will only see two wires at the light bulb, live and neutral. There may or may not be an earth depending on the type and construction of the lamp. What size is the fuse in the plugtop? What type of lamp is it?

So the 16A fuse is protecting a socket circuit I assume?

What else goes off in the house when the fuse blows?

Have you tried the lamp plugged in to another circuit?

Its unlikely that the lamp is just overloading and blowing the fuse. There may be some other appliance causing an overload/fault either.

amandstu

https://www.boards.ie/discussion/comment/122985321#Comment_122985321

As another example the power adapter on my external satellite tuner went up in mini flames before my eyes a month or so back. I saw the flame (a hot red line) come out of the adapter and advance a good inch along the cable.

No idea if those things have a fuse or not but, after initial confusion and despair I used another I had lying about and the tv worked again.

Re the bedside light I have just opened up the 3 pin plug. A bit untidy but don't think any of the loose strands on the neutral pin were touching anything metal (not now anyway)

A 13 amp fuse was in it sitting in the "live" space. There is no wire going to the "Earth" space.

If the 16A fuse in the fuse box has gone does that indicate that the 13A fuse in the plug is not working ? Or is 16A and 13A close enough for the 16A to go first? (I would be very confident there is nothing else on that circuit in use)

rob w

https://www.boards.ie/discussion/comment/122985395#Comment_122985395

That other example of equipment bursting in to flames is worrying.

Might be worth getting an electrician in to carry out a periodic test of the wiring in your house after all. Sounds like its an old installation if using fuses anyway.

Be aware that an inspection may find issues that need to be remedied, and could cost a few bob to fix, but to be honest the peace of mind to let you sleep at night its worth it.

Re the fuses blowing, in theory the 13A fuse should blow first in an overload case (assuming the lamp is causing the problem), but it doesnt always work that way in real world. And a 3A fuse would likely be sufficient for the lamp plugtop - what wattage is the lamp?

If you leave the lamp unplugged for a period of time and see if the fuse blows without it? If so, there is definitely something else going on.

https://safeelectric.ie/help-advice/periodic-inspection-reports/

amandstu

https://www.boards.ie/discussion/comment/122985346#Comment_122985346

"So the 16A fuse is protecting a socket circuit I assume?"

Yes ,we have a few fuse boxes around the house with screw in casings.That particular one just serves a few sockets including the one I use for the bedside light(the only thing actually in use on that circuit)

"What else goes off in the house when the fuse blows?"

Nothing else-just the other socket that I don't use

"Have you tried the lamp plugged in to another circuit?"

Yes.It worked elsewhere when I tried that

rob w

https://www.boards.ie/discussion/comment/122985651#Comment_122985651

I think its time to get a professional in to check the wiring then.

My understanding of this when I posted first (saying you don't need an electrician) was that the fusetop plug was blowing, I misunderstood it was actually a circuit fuse.

Not much more can be diagnosed here without someone actually looking at/testing the wiring installation.

Slightly Kwackers

https://www.boards.ie/discussion/comment/122985321#Comment_122985321

The cable will function as a fuse as I said. A fuse melts and interrupts the current, although I have worked on DC circuits where the fuse has melted as expected and not interrupted the current.

If you care to attach a length of bell wire to your kettle, you will indeed find that the wire will disconnect the power when it "blows".

It isn't the safest way of interrupting power and liable to pong a bit, but the ESB's generator will feel no pain :-)

Basically what I am getting at in a roundabout way is a 16A fuse feeding a lamp should never go and indicates a serious potentially dangerous problem if the flex to the lamp is 1mm or less.

The OP does say "There is really only that light which connects to that fuse".

Why "really" one wonders?

A 16A fault current would leave evidence unless the plug was wired live to neutral.

amandstu

https://www.boards.ie/discussion/comment/122987041#Comment_122987041

"Why "really" one wonders?"

Well that socket and another in an adjacent but unused bedroom are the only ones that I have linked to that fuse over the years.

I sometime plug the hoover into the socket in question but have not done so for a long time and I don't suppose that has any bearing on why the fuse went twice in a short timespan.

Slightly Kwackers

https://www.boards.ie/discussion/comment/122987098#Comment_122987098

Well for a start a 13A fuse is incorrect for a lamp.

A basic light should be fine with a 3A fuse.

Stick one in, tidy and remake the cable in the plug and look carefully at the lamp and cable, noting the symbols. It should have the double insulated, two square boxes one inside the other symbol.

If it looks fine, give it a go. As the 13A fuse isn't blown it seems unlikely the lamp is faulty, but a 3A fuse is better form of protection and will provide definite proof with no room for doubt that the lamp is at fault if it blows.

Your satellite power adapter sounds weird. Is there "a bit of a story" perchance?

The 12V/24V 2A devices are very common and very reliable. I never had one go like you say.

There is almost always a cement coated fuse type resistor in those supplies which just opens and the whole thing goes dead. I have never seen one that wasn't sealed either, so I can't understand how the flame was involved.

amandstu

https://www.boards.ie/discussion/comment/122987108#Comment_122987108

Thanks .I will change that fuse to the correct ampage.

Regarding the power adapter this is a double socket with 4 plugs(so two adapters in each socket)

The first socket has the wifi plus the router in the house.

The second has the tv (32 inch) power cable plus the aforementioned external satellite tuner power adapter cable.

As I said I was watching the power adapter for the external satellite tuner (can't remember if I had just plugged them in or not) ..anyway I was right in front of it when I saw the cable melt just where it joins the power adapter and I saw the red colour of burning and it seemed to snake along for short distance

Pretty dramatic but if I was to say it "went up in flames" that would be a small overstatement.

It was just an inch or so of the actual cable that turned red and (probably) smoked a bit.

I still use the same external satellite tuner now ,just with a new cable that I was lucky to come upon (from a previous dead tuner quite possibly although there were others I thought to canibalise at first that might have worked as well)

Slightly Kwackers

https://www.boards.ie/discussion/comment/122987121#Comment_122987121

Am I wrong in assuming the satellite supply is the standard 13A moulded "box" with the low Voltage cable coming out?

If so it should not happen.

If the mains feed goes in via the cable it could be a simple arc where the cable broke having been flexed near the body or plug.

There would be a smelly brown damaged bit left marking the fault area. This is not too uncommon and nothing related to wiring problems incidentally.

PixelCrafter

16 Amp Diazed / Neozed fuses will pop faster than the plug-top fuse in a 13amp plug - those things are quite slow blowing in comparison.

In a straight short circuit it's not unusual to see the Diazed fuses pop or the MCBs trip before the BS1362 fuses in the plug tops go. The comparison with the UK is also not accurate either, as the old rewardable Wylex type fuses used there were slower blowing than the plug tops. That isn't the case with the continental style cartridges used here in old wiring. They're a made to a very tight DIN spec and are genuinely a lot more predictable and reliable in reality. The repairable fuse wire stuff used in the UK was very crude.

Where the plug top fuse will blow first is usually an overload situation where it's been running at slightly beyond capacity for a while e.g. an overloaded multi-way power strip going beyond 13amps for a while.

I've even seen 3amp fuses in plugs not pop at all when 16amp Diazed fuses have popped in a short.

I'm not sure what the curve used in BS1362 fuses is, but it's definitely tending towards very slow blowing caracteristics. It seems to be designed to stay intact during short surges of load, and will blow if hot for quite a while.