Eico

[Domenic M. Mallozzi]

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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