Ten Amp Fuse in a Telly Plug (aka plugtop)

[JohnW2]

180W - even though it's LED. .... I brought it with me ....

Fair enough - but even that is well under 1A. That's obviously a lot more than current ones which, as I said seem to be in the 30-40W range for 32".

... ... and it's quite happy with the 16A RCBO.

Well, it would be, wouldn't it?! It's only if it became unhappy ('unwell') that the rating of the OPD might be of some relevance!

I hate to keep on but as most places don't have any fuses to argue about, the discussion must be purely academic.

Indeed - and, to also repeat myself, the fact that most places don;t have fuses to argue about doesn't necessarily mean that fuses could not offer them any (very slight) potential benefit.

Kind Regards, John

 

[EFLImpudence]

Well, it would be, wouldn't it?! It's only if it became unhappy ('unwell') that the rating of the OPD might be of some relevance.

Isn't that the point? Might it? Would it?

I called it the main fuse (there is another of 3.15A) because it is on the supply cable so protects everything inside.

The 6.3 and 3.15 do seem to be precise values as if it has been calculated for a specific reason.

 

[JohnW2]

Isn't that the point? Might it? Would it?

That is, indeed, the point you keep making. What is certain is that the rating of the external fuse is irrelevant when the equipment is functioning and behaving normally.

I called it the main fuse (there is another of 3.15A) because it is on the supply cable so protects everything inside. The 6.3 and 3.15 do seem to be precise values as if it has been calculated for a specific reason.

I don't think that they have been 'calculated precisely' - 6.3 and 3.15 are R10 ('preferred') Renard numbers. Interestingly, 3 and 13 aren't (although 5 is). In other words, 6.3A and 3.15A fuses are 'off the shelf' ratings.

Kind Regards, John

 

[EFLImpudence]

That is, indeed, the point you keep making. What is certain is that the rating of the external fuse is irrelevant when the equipment is functioning and behaving normally.

Why are you bringing in 'behaving normally'; we know the fuse doesn't do anything then...

...but the 6.3A is doing the same job as a plug fuse would, so it doesn't need another in a plug, does it?

I don't think that they have been 'calculated precisely' - 6.3 and 3.15 are R10 ('preferred') Renard numbers. Interestingly, 3 and 13 aren't (although 5 is). In other words, 6.3A and 3.15A fuses are 'off the shelf' ratings.

D'oh, yes. I hadn't even realise one was double the other.

 

[JohnW2]

Why are you bringing in 'behaving normally'; we know the fuse doesn't do anything then...

Quite so. I'm not really 'bringing it in', now. It was you who responded to the statement when I made it with "Isn't that the point". However, it does us no harm to remember that it must be extremely rare for a TV to cause any OPD to operate - be it your 16A RCBO, a fuse in a UK plug or whatever

...but the 6.3A is doing the same job as a plug fuse would, so it doesn't need another in a plug, does it?

No, it doesn't - which (in the case of a TV) is essentially what I said in my initial post back on page 1 (which you "liked"!). I didn't discuss the 'no fuse' option, since that can't be done with a BS1363 plug, but I did say that (for a TV) it doesn't really matter what fuse is in the plug.

Kind Regards, John

 

[stillp]

If there is no credible mechanism whereby a piece of equipment could have a massive inrush current, then it's hard to see how it could have one.

It is very credible, to me.

However, is there not a requirement for the production variability to be within the limits of the characteristic (with a specified probability). If not, then what does the latter actually mean?

I don't think the probability is actually specified, but there must be one - fuse manufacturers can't test 100% of production!

Fitted by me if the manufacturer had fitted a fuse with a rating greater than 3A.

Not really relevant then.

 

[JohnW2]

It is very credible, to me.

Fair enough - but if you can think of a credible mechanism, could you perhaps share it with us?

I don't think the probability is actually specified, but there must be one - fuse manufacturers can't test 100% of production!

As you will be aware, these things are usually done on the basis of Statistical Quality Control methods - the requirement been on the basis of the variability seen in a sample of production. As you are also presumably aware, that requirement is commonly (for not-desperately-critical products) that the mean ± 2 Standard Deviations of a sample (of specified size) should be within a range defined in the specification (which means that roughly 95% of the production run sampled should be within the specified range).

Not really relevant then.

Having just checked, it seems that I did not tell the truth! It seems that when TVs came with 5A plug fuses, I left them as they were. The remainder have 3A fuses - it's possible that they came with them, but I think it more likely that they came with fuses >5A, so I changed them to 3A ones.

My comment was (or was intended to be) 'relevant' - since I was trying to say that all my TVs had 3A fuses (no matter who fitted them) and that none of those fuses had ever failed. I now need to modify that statement to say "3A or 5A fuses"!

Kind Regards, John

 

[stillp]

if you can think of a credible mechanism, could you perhaps share it with us?

I doubt if I could explain in a manner you would accept as 'credible'.

that requirement is commonly (for not-desperately-critical products) that the mean ± 2 Standard Deviations of a sample (of specified size) should be within a range defined in the specification

IME, usually 3sigma for electronic products.

My comment was (or was intended to be) 'relevant' - since I was trying to say that all my TVs had 3A fuses (no matter who fitted them) and that none of those fuses had ever failed. I now need to modify that statement to say "3A or 5A fuses"!

Do you have enough TVs to represent a statistically-significant sample?

 

[JohnW2]

I doubt if I could explain in a manner you would accept as 'credible'.

Does that mean that many/most people would not regard it as credible.

IME, usually 3sigma for electronic products.

Fair enough - you should know. That's more demanding than I would have expected for the sort of products we're discussing. As you presumably know, mean±3 SDs will mean that about 99% of the production run sampled will be 'within spec'.

Do you have enough TVs to represent a statistically-significant sample?

Undoubtedly not, but I have had around 8 in my house for at least 30 years (albeit many of them don't get used much).

Kind Regards, John

 

[Cigaro]

It will have a SMPSU, not things known for massive "switch-on surges"

I respectfully disagree. The input stage of an SMPS consists of a rectifier followed by one (or more) massive filter caps. They can have huge switch-on surges, so much so that a room full of computer equipment can sometimes pop an MCB if all powered on at once.

Unless it has "anti-inrush" circuitry (which, admittedly, many SMPS's do), it will probably draw far more than 10 amps for a very brief period at initial power on. Not for long enough to blow the fuse, probably, but still something to be aware of.

 

[JohnW2]

I respectfully disagree. The input stage of an SMPS consists of a rectifier followed by one (or more) massive filter caps. They can have huge switch-on surges, so much so that a room full of computer equipment can sometimes pop an MCB if all powered on at once. ... Unless it has "anti-inrush" circuitry (which, admittedly, many SMPS's do) ....

Fair enough. I must say that I thought that most did (have "anti-inrush" circuitry), but it sounds as if that may not be correct.

.... it will probably draw far more than 10 amps for a very brief period at initial power on. Not for long enough to blow the fuse, probably, but still something to be aware of.

Again, fair enough. It presumably depends upon the size of the power supply, and hence the size of those 'massive' capacitors. Anecdotally, all I can say is that I have any number of SMPSUs with 1A or 3A fuses in their plugs, and cannot recall a fuse ever having blown at switch-on.

Talking of those 'massive capacitors', I would imagine that failure of one of them is the most common cause of the sort of over-current situation we have been discussing.

Kind Regards, John