Can someone confirm what the "sand" in typical cartridge fuses is put
there for? I suspect it probably has to do with quenching a high current
arc before it eats everything up. I'm looking at a 60 amp 250 vac fuse
right now which is labled "Class K5, 50,000 amps internal rating" and
which spilled sand on me when it crumbled apart yesterday as I was
pulling it out of its holder.

If arc extinguishing is what the sand is there for, is maybe a chemical
reaction involved?

My focus on fuses right now is because I've been living at home for the
past 19 years with a 60 amp GE fused disconnect which has a proclivity
for having its contacts start heating up after about a year or two of
service protecting the circuit to a HVAC heat pump air handler with
auxillary resistance make up heaters in it.

The stationary switch contacts are just the flat sides of the fuse clips
on the input end of the fuses. (The other side of those clips are curved
to match the fuse end caps.) So, when the contacts start oxidizing, they
eventually get hot enough to melt the solder joining the fuse link to
the inside of the fuse end cap, the circuit opens, and the air handler
quits.

Along the lines of "Things which go away by themselves usually come back
by themselves.", if I disassemble the switch parts and dress all the
contacting parts clean, then apply a little Kopper-Shield to them, the
darn thing works like a charm for so long that I forget about it until
we wake up to "no heat" on a cold morning and I have to climb into the
attic to fix it. I even went as far as to buy a new set of GE guts for
the thing about 8 years ago, thinking maybe the original installer had
just gotten a dud. but the same thing happened a year or so later.

Yesterday I went out and bought a Square-D non-fused disconnect to
replace that GE fused disconnect. It looks like it's got much "tighter"
contacts in it.

I understand the safety importance of having a disconnect next to the
equipment, but as the circuit is protected by a dedicated 60 amp breaker
in the home's load center, and the load is primarily resistance heating,
I think that local fusing there is redundant.

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"

Hi, Jeff.
The sand is not to quench the arc, but to hold the fusable material
steady through all those years of heating almost to the fusing point,
and then cooling. Without the sand support, the thin material would
rather quickly break.

Paul, KD7HB

wrote:

Hi, Jeff.
The sand is not to quench the arc, but to hold the fusable material
steady through all those years of heating almost to the fusing point,
and then cooling. Without the sand support, the thin material would
rather quickly break.

Paul, KD7HB


Got it, thanks!

I understand how a fuse works, but I'm always a little suprised when I
see just how small a cross section a fuse link has. The unblown 60 amp
links in those two Kentucky fried fuses I was ranting about measure
..008" thick by .065" wide at the narrow part. That's quite small
compared to the size of the wires needed to carry a 60 amp load.

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"

Jeff Wisnia wrote:
wrote:

Hi, Jeff.
The sand is not to quench the arc, but to hold the fusable material
steady through all those years of heating almost to the fusing point,
and then cooling. Without the sand support, the thin material would
rather quickly break.
Paul, KD7HB


Got it, thanks!

I understand how a fuse works, but I'm always a little suprised when I
see just how small a cross section a fuse link has. The unblown 60 amp
links in those two Kentucky fried fuses I was ranting about measure
.008" thick by .065" wide at the narrow part. That's quite small
compared to the size of the wires needed to carry a 60 amp load.

Jeff

No, that's quite small when compared to the size wire to _safely_ carry
a 60 amp load.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Tim Wescott wrote:
Jeff Wisnia wrote:

wrote:

Hi, Jeff.
The sand is not to quench the arc, but to hold the fusable material
steady through all those years of heating almost to the fusing point,
and then cooling. Without the sand support, the thin material would
rather quickly break.
Paul, KD7HB


Got it, thanks!

I understand how a fuse works, but I'm always a little suprised when I
see just how small a cross section a fuse link has. The unblown 60 amp
links in those two Kentucky fried fuses I was ranting about measure
.008" thick by .065" wide at the narrow part. That's quite small
compared to the size of the wires needed to carry a 60 amp load.

Jeff

No, that's quite small when compared to the size wire to _safely_ carry
a 60 amp load.


My, what sharp eyes you have Grandma!

Your correct of course.

Jeff (Who wonders where this thread he started is going to end up...He
sees that it's already reached the IED stage.)

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"

On Wed, 12 Jan 2005 11:55:52 -0500, Jeff Wisnia
wrote:



I understand how a fuse works, but I'm always a little suprised when I
see just how small a cross section a fuse link has. The unblown 60 amp
links in those two Kentucky fried fuses I was ranting about measure
.008" thick by .065" wide at the narrow part. That's quite small
compared to the size of the wires needed to carry a 60 amp load.

Jeff
At 60 amps, your fuse is close to melting while the wire is still
safely cool.
Gerry :-)}
London, Canada

The sand is an essential component in current limiting fuses. It provides a
heat sink and absorbent for the metal vapor created when the fuse element
blows. Without it, the fuse barrel would be filled with ionized gases and
metallic vapor when interrupting high currents. Current interruption(if it
occurred at all) would have to wait for a natural current zero before enough
time would elapse to allow the ionization to dissipate. Conversely, current
limiting fuses have the ability to interrupt the current flow well before
the first half cycle completes. This feature much reduces total energy
released by a fault, saving equipment damage and reducing fire hazard. A
side benefit is that the fuse does not vent any hot gases into the enclosure
in which it is mounted.

Randy


wrote in message
oups.com...
Hi, Jeff.
The sand is not to quench the arc, but to hold the fusable material
steady through all those years of heating almost to the fusing point,
and then cooling. Without the sand support, the thin material would
rather quickly break.

Paul, KD7HB

R. O'Brian wrote:
The sand is an essential component in current limiting fuses. It provides a
heat sink and absorbent for the metal vapor created when the fuse element
blows. Without it, the fuse barrel would be filled with ionized gases and
metallic vapor when interrupting high currents. Current interruption(if it
occurred at all) would have to wait for a natural current zero before enough
time would elapse to allow the ionization to dissipate. Conversely, current
limiting fuses have the ability to interrupt the current flow well before
the first half cycle completes. This feature much reduces total energy
released by a fault, saving equipment damage and reducing fire hazard. A
side benefit is that the fuse does not vent any hot gases into the enclosure
in which it is mounted.

Randy


wrote in message
oups.com...

Hi, Jeff.
The sand is not to quench the arc, but to hold the fusable material
steady through all those years of heating almost to the fusing point,
and then cooling. Without the sand support, the thin material would
rather quickly break.

Paul, KD7HB


Exercising some rarely displayed diplomacy I ask, "Is it possible that
both you guys are correct about what the sand accomplishes?"

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"

What if I filled my renuable fuses with sand?


"R. O'Brian" wrote in message
news:7DdFd.21187$Wo.3145@lakeread08...
The sand is an essential component in current limiting fuses. It provides
a
heat sink and absorbent for the metal vapor created when the fuse element
blows. Without it, the fuse barrel would be filled with ionized gases and
metallic vapor when interrupting high currents. Current interruption(if
it
occurred at all) would have to wait for a natural current zero before
enough
time would elapse to allow the ionization to dissipate. Conversely,
current
limiting fuses have the ability to interrupt the current flow well before
the first half cycle completes. This feature much reduces total energy
released by a fault, saving equipment damage and reducing fire hazard. A
side benefit is that the fuse does not vent any hot gases into the
enclosure
in which it is mounted.

Randy


wrote in message
oups.com...
Hi, Jeff.
The sand is not to quench the arc, but to hold the fusable material
steady through all those years of heating almost to the fusing point,
and then cooling. Without the sand support, the thin material would
rather quickly break.

Paul, KD7HB

On Wed, 12 Jan 2005 18:51:06 GMT, Tom Gardner wrote:
What if I filled my renuable fuses with sand?

You'd change their characteristics in unknown ways. Why would you
do that?

The least of my worries if the "Fuse Police"! Do you think I alter their
characteristics when I double-up the links?
(Actually I have fazed-out renewables in favor of 1-times due to advice I
got here and I am better for it.)


"Dave Hinz" wrote in message
...
On Wed, 12 Jan 2005 18:51:06 GMT, Tom Gardner wrote:
What if I filled my renuable fuses with sand?

You'd change their characteristics in unknown ways. Why would you
do that?