"MEC" wrote in news:1166737416.477032.162250@
42g2000cwt.googlegroups.com:

Hi,
The glass type 5A fuse in the switch to my tiller pilot blew the
other day. The manual calls for a 12A fuse. Replaced fuse with one from
local hardware shop but switch wont function at all with this one. It
was a 15A 3AG or 3WG (will replace with 12A asap). Is this because it's
a 240V fuse? Are there fuses specifically for 12V DC? Have tried other
switches with fuse with same result.

Thanks for your advice in advance



No, The 240V rating on the fuse is the highest circuit voltage the fuse
is rated to interrupt. At higher voltages, its melted-open gap may arc
when it melts. You may use a 240V fuse on any circuit LESS than 240V.
12V is fine....

Did the 15A fuse blow, too?

Fusing on a circuit is normally quite a bit more than the circuit
actually draws but no more than the wiring the fuse protects is rated
for. Europeans fuse their equipment lots closer than Americans, which is
sometimes frustrating with nuisance blows on good equipment, just because
there was a momentary current charging power supply capacitors or the
like, for instance. If it draws 10A, fuse it for 15A, 50% over normal
load. Fuses do NOT protect fragile electronics from surges. Fuses are
thermal beasts and FAR slower to blow than diodes, transistors, ICs, and
other electronic components. To protect electronics from voltage surges
on DC circuits, we use a special sensing IC that fires a device to ground
the offending overvoltage condition, blowing the fuse, when the fuse gets
around to it. Under no circumstances will those protectors allow
overvoltage to appear on the protected electronics.

Of course, those protective circuits cost money and reduce profits, so
most consumer electronics, such as you buy for your boat, don't have
them. We need to sell you new stuff at regular intervals, planned
obsolescence, you know. The other trick is to put something like charts
on proprietary memory ROMS noone else is allowed to produce. After the
next series of chartplotters comes out, you simply stop producing charts
for the one you want to die, like my Garmin GPSMAP 185S. You put
"Discontinued" on its webpage, trying to render it useless and valueless
so they all have to go buy the next generation of nonsense they don't
need. It's an old NMEA trick that's worked for years.....

The other trick is to come out with a "new, improved" version of
incompatible NMEA data at a different rate.....NMEA 2000.