Eico

[john]

There's a lot to the humble fuse. I think the ubiquitous 3AG is a 250V
part, because that's the max voltage it can open with certainty, without
sustaining arc/plasma conduction.

Fuse curves are interesting. Its scary how long a 1 amp fuse can run with
1.2 A (for example) before opening .... (hint...it's a considerable time!)

Happy new year all!
John


At 11:44 AM 12/30/00 -0500, you wrote:
>Interesting Don. Looks like though, in most small audio amplifiers
>and receivers, transmitters up to say 100W, that if you added a
>small fuse or two on the secondary, say for example, a 1 amp
>pigtail, it could only help. Surely it wouldn't arc, and if it only
>seperated by 1/8" when it blew and arc'd over to the rest of the fuse
>material, THAT would soon blow too? No holder needed anyway.
>
>I am sure now that there is a lot more to this than what I had
>thought!!
>
>Happy New Year chaps!
>
>On 1 Jan 2001, at 11:12, DMallozzi at aol.com wrote:
>
>> Hi gang
>>
>> Regarding Brian's comments about why manufacturers did not use HV voltage
>> fuses on the secondaries I can venture a few guesses.
>>
>> First, (and probably the big driver) is the expense of the fuse and the
>> holder are much more than the usual 250 V fuse.
>>
>> The HV fuses are physically much larger and therefore in smaller equipment
>> become a mechanical issue.
>>
>> Third, many applications we are discussing do not draw large secondary
>> currents and the high voltage fuses are typically not available in a lot of
>> currects below 1 A.
>>
>> I have had a little experience using fuses at high voltages (up to 50,000
>> VDC) and I can tell you that the use requires some thought. Also, there are
>> techniques similar to fuses I have seen in use at above 5 KVDC but they are
>> not appropriate for consumer applications.
>>
>> I had the occassion in one job to test some fuses (250 V) at 5 to 10 times
>> there ratings in standoff voltage. The results were things like arcs and
>> plasmaing that result in the fuse not interrupting a fault. Some of this is
>> due to physical size and construction. The remainder is usually a result of
>> the way the fuse link deteroriates. In some fuses to stop the arcing/plasma
>> scenario the link is surrounded by a material similar to sand (don't have a
>> clue what it actually is) that physically fills the path between the
ends of
>> the broken link.
>>
>> If anyone has more insight to this I would like to hear it.
>>
>> 73's and a Happy and Healthy New Year to all
>>
>> Dom
>> N1DM
>
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