Do main cut-out fuses age ?

[Licklieder]

In posting a comment to another thread, i mentioned that i think the main cut-out fuse on my install is probably the original from ~1970 or about 50 years old by now. which got me to thinking - does the time-current characteristic curve degrade with time?

The only BS1361 chart i have been able to find ( https://www2.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=64556 ) would seem to indicate that at 100A, the specified blow time for an 80A fuse is off the chart at > 10,000 seconds (~2.5hrs). It is a bit of an academic question, but my curiosity i piqued - would a 50 year old fuse still have the same characteristic or would it have degraded ? if so, by how much?

 

[bernardgreen]

would a 50 year old fuse still have the same characteristic or would it have degraded ? if so, by how much?

They do degrade, but by how much will depend on many things.

Fuse wire exposed to the atmosphere can oxidise and become thinner.
Temperature cyclic with load currents close to or above the rated current will affect the wire

But in most cases the degrading of the fuse wire in a hermetically sealed cartridge fuse will be small enough to be insignificant

 

[securespark]

Yeah, I have had fuse wires deteriorate and rupture due to old age.

 

[JohnW2]

Yeah, I have had fuse wires deteriorate and rupture due to old age.

Me, too, in the fairly distant past - but, as bernard has said, one would expect much less/slower deterioration in the case of a hermetically sealed cartridge fuse.

It seems that, like the OPs, a lot of cutout fuses have been in service 'for ever'. Do people ever see instances of them blowing 'spontaneously' (i.e. 'for no good reason')? My experience is obviously very limited, but I don't think it's something I have ever heard of happening.

Kind Regards, John

 

[BS3036]

When we moved into our house, a long time ago, we had the main fuse blow after about a year. It was not related to any exceptional load. I gather now it was probably a 60A fuse. That's the only time, and the guy who came to fix it said 'it just happens now and then, because of old age'.

 

[JohnW2]

When we moved into our house, a long time ago, we had the main fuse blow after about a year. It was not related to any exceptional load. I gather now it was probably a 60A fuse. That's the only time, and the guy who came to fix it said 'it just happens now and then, because of old age'.

I suppose that's consistent with what I've seen/heard (or not) - i.e. I'm sure that it must happen occasionally, even if only once in a blue moon, but in all the decades I've been around, I don't recall ever having heard of it happening amongst my friends/family/colleagues etc.

Kind Regards, John

 

[securespark]

BS3036.....Was it a BS 3036?

 

[BS3036]

 

[Licklieder]

Thanks all. my take on it all is that yes, they do age but you just leave them be until / if /when they do pop.

My initial thinking was that age would be the main factor in deteriorating performance, without thinking through the causes. if i'd thought about it a bit more, i would have got to atmospheric oxidation and thermal cycling as bernardgreen pointed out. Bit a brain fart moment really - i used to work in a lab performing materials testing. once my brain started working again, i surmised that for encapsulated fuses that the prime aging mechanism is thermal mechanical fatigue - and with a bit more digging on Google, i managed to find some websites/dicsussions that do seem to confirm that, though they would seem to be more of an issue with Zinc based fuses than Copper or Silver.

My curiosity has been tweaked now and i'm wondering whether its possible to predict the expected lifetime....

 

[JohnW2]

My curiosity has been tweaked now and i'm wondering whether its possible to predict the expected lifetime....

That would presumably depend crucially on the nature of its service - if, for example, constant dramatic thermal cycling were involved (particular if involving currents up to, or beyond, the rating of the fuse), one might expect life expectancy might be appreciably reduced.

However, for the common situation in which an encapsulated fuse spend most of its life carrying currents well below its rating (and particularly if the current were relatively 'constant') I would imagine that the expected lifetime might well be 'many decades', if not more - probably far longer than would facilitate any empirical investigation. 'Accelerated testing' is all very well, but one never knows quite how that will relate to non-accelerated service!.

Kind Regards, John