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Should fuses be in plug tops

adrian92

Do these fuses serve serve any useful purpose,

or just complicate the plug top components ?

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Baseball72

I'm not n electrician but fuses in a plug prevent fuse boards from blowing completely. If a plug hasn't a fuse you shouldn't use it...

Tell me how

adrian92 wrote: »

Do these fuses serve serve any useful purpose,

or just complicate the plug top components ?

They serve a purpose.

They limit potential current flow to a device to usually 13A or possibly 5A or even 3A.
This is necessary on devices which can have very small gauge wire which might not stand up to the 32A which could be available from the consumer unit on some circuits.

adrian92

I take your argument , but I have never seen a 13 Amp plug top fuse fail with a short circuit in the appliance.

Always it is the Distribution Board MCB or RCD which has isolated the fault.

Charles Babbage

Fuses in plugs are a consequence of ring circuits,but if the proper fuse is used it can also limit the current on thin leads as the previous poster said.

Tell me how

adrian92 wrote: »

I take your argument , but I have never seen a 13 Amp plug top fuse fail with a short circuit in the appliance.

Always it is the Distribution Board MCB or RCD which has isolated the fault.

There are different types of overload scenarios.

But, in cases where there might be a fault on the non-fixed device which increases current flow significantly, say to about 18A, without it being a direct short, then the likelihood of serious damage would be much greater without an appropriate fuse.

Victor

Also limits the current if the cable is damaged.

Always Tired

The US type doesn't have them. And then the fuse box has fuses that blow and need to be replaced (in the dark). Used to happen if you switched things on and off quickly. Here I rarely have had surges hit the fuse box and it's much better to just have it be a switch that you can push back to solve the issue.

adrian92

But what is the purpose of a 13 Amp fuse in a plug top.

How often do they provide protection?

adrian92

There must be of the order of tens of millions of appliances in Ireland with 13 Amp fuses fitted.

There have been electrical faults on some appliances over the years.

Does anyone know any occasion that the 13 Amp fuse , in the plug top, isolated the fault?

2011

Tell me how wrote: »

The short circuit is very high current but for a very short amount of time and MCB's can operate very quickly, and particularly when compared to a fuse.

It’s actually the other way around. Under short circuit conditions fuses can operate quicker than breakers. This can happen to the point that discrimination is lost.

kramer1

Lso good for stopping people over loading extension leads

adrian92

kramer1 wrote: »

Lso good for stopping people over loading extension leads

Can anyone say how a 13 Amp fuse has provided electrical protection ?

I still do not understand why we put fuses into plug tops

L1011

adrian92 wrote: »

Does anyone know any occasion that the 13 Amp fuse , in the plug top, isolated the fault?

Yes. Lots

Why do you think replacement fuses are sold? For fun?

endacl

adrian92 wrote: »

But what is the purpose of a 13 Amp fuse in a plug top.

How often do they provide protection?

All the time.

adrian92

endacl wrote: »

All the time.

How?

deandean

Like Adrian92 i have never seen a 13 amp plugtop fuse blow. In the event of an appliance or flex fault I have always seen the MCB trip first.
The plugtop fuse in a lot of appliances is way over rated. Like a 13A fuse in a table lamp1

Bruthal

adrian92 wrote: »

But what is the purpose of a 13 Amp fuse in a plug top.

How often do they provide protection?

Well any devices are providing protection even when they never operate.

Plug top fuses are a debatable topic though. They are probably useful in extension leads.

seamus

adrian92 wrote: »

Can anyone say how a 13 Amp fuse has provided electrical protection ?

I still do not understand why we put fuses into plug tops

The fuse in the plug top limits the maximum amount of current that can be drawn into the appliance.

In the case of a multi-gang extension lead, this means that no matter how many appliances you connect to it, or how far you daisy-chain it, the total current will never exceed 13 amps.

Back in the 1980s and earlier, it was common for people to use multi-adapters. These allowed you to plug multiple appliances into a single socket. Like this, but back then the adapter was often unfused. Tended to be fine if you were plugging in a kettle and a toaster together. But it was common for people to daisy chain them too. And use them to plug in heaters and washing machines. And before you know it you have 25 amps flowing through the adapter. Fires were common.

How the fuse in the plug top provides protection is by blowing before the appliance goes on fire. The ring circuit typically has a fuse/breaker rated for 30/32 amps. Your typical appliance is not. If a fault developed in the appliance that caused it to draw 30 amps, then if you're lucky the cabling or circuitry will blow, and that's that. If you're unlucky it will go on fire. If your appliance's plug has the correct fuse in it, then the fuse will pop before anything goes on fire.

This is not a concern in other countries because they tend to be wired differently.

Tuco88

I think the bread and butter of the fuse was to protect the flexible cable supplying the appliance... More so than the appliance itself.

The fuse size is incorrectly too large at times, like for table lamps and such.

Lots of poor quality ones out there. They fail alot (what I see anyway) before the fuse on the metal base thats attached to the fuse holder on cheap brands.

Bruthal

A 13 Amp fuse will allow currents above 13 amps to flow for a while. 15 or 16 amps could flow for quite a while.

Single appliances won't really overload its cable. Typically any faults are short circuits.

kramer1

I've seen them blow, dead short at a boiler, was probably a 3 amp

adrian92

Well,

It would be of interest to me to know if anyone can give an example of how a 13A fuse in a plug top has provided electrical protection

2011

adrian92 wrote: »

Well,

It would be of interest to me to know if anyone can give an example of how a 13A fuse in a plug top has provided electrical protection

The 13A fuses in overloaded extension leads have been known to blow preventing the conductors within the cable overheating, melting the insulation and going on fire.

As a rule fuses operate more quickly than MCB's under short circuit conditions. Therefore a short circuit within equipment plugged into a socket often results in the fuse within the plug operating.

Both of the above examples show how plug top fuses provide a degree of protection.

It is important to understand that MCB's that socket circuits are fed from (generally rated from 16 to 32A) can not provide over current protection to leads on appliances that may only have 0.75mm sq. conductors.

Bruthal

They don't actually have to operate to have provided protection.

As in, the circuit after the fuse is protected from over-currents above what the fuse will fail at. Protection that is not needed I guess we could say, if there never is an overload. Passive protection.

Maybe the question should be, has anyone seen them disconnect an appliance or extension lead.

LeBash

adrian92 wrote: »

Well,

It would be of interest to me to know if anyone can give an example of how a 13A fuse in a plug top has provided electrical protection

Many many moons ago I worked in a wholesaler and we sold plug top fuses over the counter more than once everyday. I'd say we used to go through 200-300 per month across the range. Boilers, table lamps, brown goods, white goods, glass 20mm quick blow fuses in microwaves, old school Christmas lights.

When hair straighteners became a thing at first, we would see at least 1 everyday with a fuse blown. Hair dryers were another one that appeared regularly at the counter.

We would change them for the old dears who would come in and God Bless the lad who invented the 13a plug top where you could pop the fuse out without opening the whole thing.

adrian92

LeBash wrote: »

Many many moons ago I worked in a wholesaler and we sold plug top fuses over the counter more than once everyday. I'd say we used to go through 200-300 per month across the range. Boilers, table lamps, brown goods, white goods, glass 20mm quick blow fuses in microwaves, old school Christmas lights.

When hair straighteners became a thing at first, we would see at least 1 everyday with a fuse blown. Hair dryers were another one that appeared regularly at the counter.

We would change them for the old dears who would come in and God Bless the lad who invented the 13a plug top where you could pop the fuse out without opening the whole thing.

Thanks for that. I wonder. though, if the 13A fuses were used to replace the failed fuses with a lower rating, such as 3A fuses?

2011

adrian92 wrote: »

Thanks for that. I wonder. though, if the 13A fuses were used to replace the failed fuses with a lower rating, such as 3A fuses?

I believe that this is a very common occurrence.

Dardania

I agree that they serve a useful purpose for sure (particularly for short circuits), however I wonder if their utility / need is reduced due to presence of the ELCB since the late 80s?

Before the ELCB, any field short to ground would just flow away until a overload device would catch it like a fuse. Having a fuse rated close to the device rating probably helped with that, particularly if on a ring circuit.

But nowadays we have ELCBs / RCBOs which catch a common issue, double isolated devices, more stringent CE making with better quality products etc... maybe the risk having a local device specific fuse justified has been mitigated by other means.

2011

They serve completely different purposes.
Fuses and MCBs are for protection against over current conditions (sustained overload and short circuit). Whereas an RCD (or ELCB as they were previously known) is checking that there is no imbalance between the current in the phase an neutral of a final circuit.

Depending on the nature of the fault one device may operate and the other may not.

Bruthal

Well the rcd will sometimes save a fuse from blowing.

But many devices dont have any earth conductor in their leads, so it will do nothing on those in terms of fault tripping.

So they dont really reduce the need for plug fuses, if there is a need for them.