Fuses on Xmas tree lights

We always run out of the fuse bulbs, and there are so many different light-sets that it is difficult to get replacement fuse bulbs.
It seems to me that it would be much simpler if there were a fuse in the plug, with a specified amperage.
Is there anything one can do along these lines?
--
Timothy Murphy
e-mail (<80k only): tim /at/ birdsnest.maths.tcd.ie
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Nope!
The problem isn't that bulb failure results in the set drawing a higher current, this stays the same, except the same amount of current is now distributed amongst fewer bulbs.
Sparks...
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Sparks wrote:

That's completely wrong. Failed bulbs go short circuit, so the total resistance in the series circuit falls and the current rises. The remaining bulbs are over-run and thus more likely to fail too. Eventually a chain reaction occurs and, without the fuse bulb, you'd end up with a short across the mains, possibly setting fire to the thin wire.
The fuse bulb, if present, should stop the chain reaction before it's got too far. I suppose a 2 A plug fuse would protect the wiring and prevent a fire, but not until you'd lost all the other bulbs. (1 A plug fuses are available, but aren't ASTA or BSI approved and shouldn't be used.)
--
Andy

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There are plenty of 1amp fuses that meet BS1362 and there is no reason not to use them.
For example - http://uk.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU 23029
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dcbwhaley wrote:

It's not whether they comply with BS 1362 that matters, it's whether the particular fuse has an ASTA or BSI approval certificate to that standard. It used to be the case that the 1 A rated types (which aren't sand filled) weren't so approved.
However, having just looked at the data sheet for the Bussmann TDC180 I see it says that the 1 A version is approved, so I stand corrected. I'd still check that the fuse has the approval markings before using it though.
--
Andy

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Andy, could you explain that to me in words of one syllable. Complying with a BS doesn't mean that it is BSI approved?
(This is a genuine request for information not a sarcastic comment)
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dcbwhaley wrote:

Complying with a standard just means that the product meets all the (relevant) requirements of the standard. A manufacturer could be confident of this by design plus testing if necessary. This testing could be done by the manufacturer himself.
Without any reference to a third party, you've only got the manufacturer's word for it. They could be wrong, or even telling lies.
An approval certificate, OTOH, is evidence of third party examination and testing of the product by a approval body, themselves vetted. The approval process will also usually examine the manufacturer's ability to continue to produce compliant product (i.e. their QA system). The approval results in a licence to apply the approval mark of the approval body (a certification trade mark) to the product for a set period of time.
HTH
--
Andy

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Sorry Andy but I must be very thick 'cos I still don't understand.

What more can you ask than that a product meets all the requirements of the standard? If it walks like a duck etc then it is a duck.

But you just said that "Complying with a standard means that the product meets all the requirements of the standard". Did you mean to say that complying with the standard doesn't always mean that the product meets all the requirements of the standard?
So what is the point of the standard?
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dcbwhaley wrote:

The manufacturer says so versus an independant 3rd party says so. Even a plastic toy can be called a duck, and walk like a duck, but not be a duck.
NT
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That I could understand. But Andy says "Complying with a standard just means that the product meets all the (relevant) requirements of the standard. ". If the BS means that it "meets all the (relevant) requirements of the standard." what further reassurance can another certificate give?
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Test by an organisation other than the manufacturer and certification by them.
Another common example of this comparison is CE marking on products. For most classes of product is part of a self declaration by the manufacturer or importer that the product meets the standards relevant to that product. There is supposed to be a Declaration of Conformity signed by an officer or other responsible person of the supplier which includes which standards are involved. Reputable manufacturers do this as well as having on file supporting test reports from an appropriate test house.
To some extent, the exercise is a farce because it is not very actively policed, although there could be repercussions if Something Bad happened and it was found that the manufacturer/importer did not have their ducks in line. It's certainly open to abuse in the form of the archetypal Chinese toy manufacturer who puts a CE label on the box and the only thing that meets type requirements is the box.
There are classes of product where it is a *requirement* to use an outside test house and to be able to produce reports - some machine tools are an example of that.
In the past, I've seen all sorts of weasel phrases in product marketing literature - e.g. "designed to meet standard blah-blah" does not mean that it actually does.
In the end, for the consumer, it comes to credibility and trust. For items where safety is critical, I will only buy from very well known manufacturers who I believe will have done the proper testing or had it done and who can be reasonably relied upon not to have bent or broken the intent of the legislation and standards; and who will have product liability insurance in place.
None of this is a cast iron guarantee, but to my perspective it's a far better approach than buying goods of unknown origin via a volume retail supplier.
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I don't know about BS1362 fuses, but BS1363 (plugs, sockets, etc) are regarded as so critical to safety that I believe it is required that they are tested by an independant body, and that the testing is performed to destruction. Same may apply to BS1362, and that maybe why non-ASTA approved BS1362 fuses are not permitted in plugs.
--
Andrew Gabriel

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dcbwhaley wrote: NT:

A BS marking doesnt mean it meets BS. It means I the manufacturer, who have a lot of money and my own job riding on this, am claiming it does.
NT
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dcbwhaley wrote:

The manufacturer says so versus an independant 3rd party says so. Even a plastic toy can be called a duck, and walk like a duck, but not be a duck.
NT
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The heat and consequent light of a bulb is generated by current. If the bulbs get brighter when one blows, then it must be because the current has increased. The voltage of the mains is distributed over fewer bulbs, so each gets a higher valtage. As the voltage increases, the current increases, and that increases the heat, but also increases the resistance, providing some negative feedback, but the current does still increase.
I suspect though, that the current increase is fairly small, and so the fuse bulbs need to be very sensitive.
-- JJ
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a) don't buy them at all
b) keep a complete spare set of lights and when the first set fails throw the whole thing away and use the replacement.
c) Buy a replacement set for the replacement on Christmas Eve for 3 and remind yourself of (a)
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Check out wholesalers shortly after the holiday. They near give them away.
--
*Elephants are the only mammals that can't jump *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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I bought two sets for 50p each a few years ago post-Christmas, and the sodding things refuse to die.
--
Skipweasel
Pay no attention to that man behind the curtain.
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Timothy Murphy wrote:

Unfortunately the fuses for 13A plugs are 3A and 13A, with other ratings for FCUs.
I don't think a fuse of the lower rating needed for Xmas tree lights would have the breaking capacity to be suitable for use as a plug fuse, and there would always be the risk that someone would substitute a 13A fuse.
A fuse-bulb is cheapest for the manufacturers, and when you consider the rock-bottom price of many of the sets, cheapness is what counts.
Fuse-bulbs shoulnd't be blowing that often - unless lots of ordinary bulbs have already blown, or you've replaced some bulbs with the wrong rating.
Owain
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Owain wrote:

If its a modern set with shorting bulbs, and you dont use a fuse bulb, if 2 or 3 bulbs go then thers start going faster, and you get a chain reaction of bulbs blowing. As this happens, remaining bulbs get more and more power eacha nd start popping uberfast ,until theyre all shorted. Then the plug fuse goes. You're left with a 100% dead set, plus the risk of bulbs shattering and sort of explodng along the way. IOW use a fuse bulb.
If its an old set with non shorting bulbs, a fuse bulb is not particularly important, and those old sets can safely run without one. Every bulb acts as a fuse. But if you put modern shorting bulbs in, this changes.
NT
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