PIV electrics

[stillp]

not one scrap of evidence that fused plugs provide any benefit in reducing fires originating in appliances

Other than that which can be deduced by anyone with a basic knowledge of elementary physics, no.

so you are not arguing that the purpose of fuses in plugs is to provide any protection to the internals of appliances

I am not arguing anything about the purpose of fuses. I am arguing that it is a fallacy to state that fuses only protect the cables and not the appliances connected via those cables, and that the lower the value of the fuse, the more protection is provided to the appliance (and its cable).

If the protection provided by the fuse in the plug is to be closer than the protection provided by something else, what something else could there be apart from the circuit OPD?

Read the whole exchange. My statement was in answer to EFLI's "why was it considered necessary to fit other rated fuses in the plug"
The protection provided by a lower value fuse is closer than the protection provided by a greater value. Don't you realise that?

In circumstances where veracity of evidence is considered important, hearsay evidence is not allowed.

Since this is an internet forum and not a court of law, that is hardly relevant.

So I guess it is up to you to decide how important it is here that what you say should be regarded as true.

I have little hope that what I say here will be accepted by you as being true, since it is a view that differs from yours.

 

[stillp]

Evidence and rationality.

Is it not rational that smaller value fuses allow less let-through energy than larger fuses? Do you need evidence of that fact?

 

[EFLImpudence]

Is it not rational that smaller value fuses allow less let-through energy than larger fuses?

It is, but that is not the fundamental point, though, is it?

Rather, it is - would these, by definition, small appliances - be saved by limiting this let-through energy should they develop a fault?
This, of couse, presumes the manufacturer has not made provision for this by designing the product to fail safely, by including, if not a fuse, then a weak link, when he knows that it will likely be on a 16A circuit in most places.

It, surely, is only short-circuits or eath-faults as these appliances are unlikely to cause an overload sufficient to rupture even a low rated fuse.

Do you need evidence of that fact?

Not of that fact, but it would be good to have an example of an item where this limited let-through energy would be advantageous by, supposedly, saving the item from damage - or unwanted consequences - that they must sustain in the rest of the world.


I am actually having a bit of trouble thinking of a product to which this applies.
Extractor fans are in my mind and the usual topic for 'fuse needed or not'.
Fitting 3A or 1A fuses to television plugs (other thread) is obviously not necessary so that was a red herring. The subject need never have been raised.
Electronic items have wall-warts.

I have a 12W glue-gun (bought here). Should I fit a British plug to it with a 50mA fuse?
That may be a silly example but it is what you are saying.

 

[stillp]

I have a 12W glue-gun (bought here). Should I fit a British plug to it with a 50mA fuse?
That may be a silly example but it is what you are saying.

No it isn't what I'm saying!
If it had a BS1363 plug, what fuse would you fit?

 

[JohnW2]

It is, but that is not the fundamental point, though, is it? Rather, it is - would these, by definition, small appliances - be saved by limiting this let-through energy should they develop a fault?

As I have said, in the majority of cases it probably wouldn't make an appreciable difference - since, by the time some malfunction (everyday 'fault') has resulted in enough current to blow any fuse (and that includes any internal fuses) it's very likely that the device will have been damaged beyond realistic/cost-effective repair. However, there presumably must be some (even if rare) 'borderline' cases, in which the lower let-through energy of a lower-rated fuse (as compared with, say, that of a 16A MCB) might just make a difference.

This, of couse, presumes the manufacturer has not made provision for this by designing the product to fail safely, by including, if not a fuse, then a weak link, when he knows that it will likely be on a 16A circuit in most places.

Indeed, as I said (or implied) in my very first response, in the case of something like a TV which will almost always have internal fuses, from the point of view of the equipment, there is no point in having any external OPD (and that includes the circuit's OPD, which is therefore only needed to protect cables) unless it is such that it would be likely to operate before the equipment's internal fuse(s).

Electronic items have wall-warts.

Some electronic items have wall-warts. For what it's worth, none of my items of AV equipment have wall warts, and few of my items of IT equipment do. Most either have internal power supplies or an external one which is powered via a cable and BS1363 plug/socket. I couldn't tell you how many of these items have (adequate) internal protection.

Kind Regards, John

 

[EFLImpudence]

However, there presumably must be some (even if rare) 'borderline' cases, in which the lower let-through energy of a lower-rated fuse (as compared with, say, that of a 16A MCB) might just make a difference.

You can't just keep saying that.
If you cannot quote a definite example then it cannot be a reason.

 

[EFLImpudence]

No it isn't what I'm saying!

Yes, it is.
You say you would fit the lowest rated fuse that would allow the device to work.

If it had a BS1363 plug, what fuse would you fit?

As I have said, for a customer I would fit a 3A because otherwise they might mistakenly think I had done something wrong - like the poster with the TV.
They may even say, if thinking like you, "Why didn't you fit a 50mA one?" - because there are none which fit - Why not?

For my own, I may very well fit a 3A as I have some and don't want to use all the 13A ones.
I obviously cannot fit it in the kettle so using it because it is there is not trapping me into admitting anything.

I have said these things (3/5A fuses) are only used because they are there, not because they are needed for electrical reasons.
Perhaps they are only made because of erroneous instructions by manufacturers when selling in Britain or, originally, mistaken beliefs by those who devised the ring circuit necessitaing fused plugs and they, like you, thought it would be a good idea.

Entrenched beliefs, no matter how misguided, are difficult to eradicate.

 

[stillp]

Entrenched beliefs, no matter how misguided, are difficult to eradicate.

Yes, including the belief that the only benefit of plug fuses is to protect cables.

 

[stillp]

Yes, it is.
You say you would fit the lowest rated fuse that would allow the device to work.

I'm pretty certain that the BS doesn't include 50 mA fuses.

 

[EFLImpudence]

Hence: "because there are none which fit - Why not?"

 

[stillp]

Because currents that can blow a fuse below 1A don't need sand-filled ceramic fuses to achieve the rupturing capacity?

 

[JohnW2]

You can't just keep saying that. If you cannot quote a definite example then it cannot be a reason.

I don't think you can keep saying that, either!

I'm not sure what you actually mean by 'a definite example'. If you're talking about 'an actual case', as I've said before, that is impossible - since, if there was an external low-rating fuse when 'something happened', one cannot know what would have happened in the absence of the fuse and, similarly, if there were no external low-rating fuse, one cannot know what would have happened if there had been one - just as one cannot know whether the presence of an RCD had resulted in an electric shock being non-fatal, or whether the presence of an RCD (when there wasn't one) might have prevented a shock being fatal.

The magnitude of the excessive current which flows when something goes wrong within a piece of equipment obviously cannot be altered by any protective device, but the device may be able to limit the duration of that current (i.e. reduce the 'let-through energy').

Do you agree that, at the extremes, a 'moderate' excessive current would probably not, in itself, do any additional damage (although damage may already have been done by the primary fault) if it persisted for only a few microseconds, but may well do damage if it persisted for a much longer time (or 'indefinitely')? Getting a bit less extreme, do you also agree that the amount of 'additional damage' is quite likely to increase as the duration of the excessive current increases?

If you agree with the above, do you not accept that a device which 'clears' the excess current more quickly might, at least sometimes, result in less damage?

Kind Regards, John

 

[EFLImpudence]

Because currents that can blow a fuse below 1A don't need sand-filled ceramic fuses to achieve the rupturing capacity?

So, you cannot afford protection below a 3A fuse - plus its fusing factor?.

Surely you think that is not good enough.

 

[EFLImpudence]

If you agree with the above, do you not accept that a device which 'clears' the excess current more quickly might, at least sometimes, result in less damage?

Not in any way which would be beneficial.

 

[EFLImpudence]

From BEAMA.

No mention of any appliance.

http://www.beama.org.uk/asset/A3738A16-B693-4354-9BA38AB49204773F/