On Fri, 23 Mar 2012 13:33:04 +1100, "Phil Allison"
wrote:


"Jeff Liebermann"

The coffee distillery is double insulated, which means it doesn't need
a ground pin on the power plug. Since a fault can affect either side
of the power line in such a symmertical arrangement, two fuses are
required.

** Horse manure.

Yep. My neighbors just unloaded some Llama manure in their "garden".
Doesn't smell too bad.

One fuse is sufficient to break the circuit in case of current overload.

http://www.freewebs.com/valvewizard/fuses.html
Some appliances use two fuses, one for live and one for
neutral. While there is some argument against using a
neutral fuse, there is no law against it (in the UK anyway).
You can buy IEC inlet sockets with built-in fuse holders,
which greatly simplifies construction.

http://www.appliance411.com/faq/dryerheat.shtml
There are 2 fuses or breakers for the dryer, both must
be good in order for the dryer to function properly.

Note that the thermal fuses also act as an internal short
protector.

** Even worse horse manure.

Well, there are things worse than horse manure. I've never tried
skunk manure, but I suspect that would qualify.

Thermal fuses act on temperature, not current at all.

True.

The max current rating given by makers is based on self heating to ensure
the fuse stays within temp rating tolerance.

The max current rating is the maximum current at which it will operate
safely without self-heating and blowing the fuse. I found out the
hard way that it's much like the rating on a typical wire fuse. If
you run a 5A fuse, at 5 amps at room temperature, it will eventually
blow. Same with a thermal fuse. If you run it near it's rated
maximum current (usually 5A, 15A, or 30A), it will eventually get warm
enough to melt the wax and trip the fuse. With a short circuit across
the power line, the self-heating will blow the thermal fuse almost
instantly. It's not designed to be a power fault protection device,
but does the job nicely anyway.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Jeff Liebermann = Nut Case ****wit "

The coffee distillery is double insulated, which means it doesn't need
a ground pin on the power plug. Since a fault can affect either side
of the power line in such a symmertical arrangement, two fuses are
required.

** Horse manure.

Yep.

** Glad you agree- ****wit.


One fuse is sufficient to break the circuit in case of current overload.

http://www.freewebs.com/valvewizard/fuses.html
Some appliances use two fuses, one for live and one for
neutral. While there is some argument against using a
neutral fuse, there is no law against it (in the UK anyway).
You can buy IEC inlet sockets with built-in fuse holders,
which greatly simplifies construction.


** Utterly irrelevant crap.


http://www.appliance411.com/faq/dryerheat.shtml
There are 2 fuses or breakers for the dryer, both must
be good in order for the dryer to function properly.

** That schem shows TWO PHASE power being used.

You ****ing tenth wit.



Thermal fuses act on temperature, not current at all.

True.

** Glad you agree - ****head.


The max current rating given by makers is based on self heating to ensure
the fuse stays within temp rating tolerance.

The max current rating is the maximum current at which it will operate
safely without self-heating and blowing the fuse.


** There is only a few degrees of self heating at the rated current.

So to melt the material inside takes at least 5 times that current.


I found out the
hard way that it's much like the rating on a typical wire fuse. If
you run a 5A fuse, at 5 amps at room temperature, it will eventually
blow.


** Wire fuses run very hot at rated current, the wire inside may bend or
even glow in the dark - ie nothing like thermal fuses.

Same with a thermal fuse.

** Blatant LIE.

If you run it near it's rated
maximum current (usually 5A, 15A, or 30A), it will eventually get warm
enough to melt the wax and trip the fuse.

** MASSIVE BULL**** !!!!!!!!!!


With a short circuit across
the power line, the self-heating will blow the thermal fuse almost
instantly.

** Nope - it will trip the supply breaker.

With a 10 times or more overload, breakers trip in a few milliseconds.

You stupid asshole.


.... Phil

On Sat, 24 Mar 2012 08:48:09 +1100, "Phil Allison"
wrote:

If you run it near it's rated
maximum current (usually 5A, 15A, or 30A), it will eventually get warm
enough to melt the wax and trip the fuse.

** MASSIVE BULL**** !!!!!!!!!!

With a short circuit across
the power line, the self-heating will blow the thermal fuse almost
instantly.

** Nope - it will trip the supply breaker.

With a 10 times or more overload, breakers trip in a few milliseconds.

You stupid asshole.

See: UL 60691 for testing of the the thermal fuse:
http://bbs.dianyuan.com/bbs/u/32/1122972217.pdf
Section 10.8 discusses its use as a short circuit protection
overcurrent fuse. (This is rev 3. Rev 5 is the current version).



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Thursday, March 22, 2012 12:03:41 AM UTC-4, jeff_wisnia wrote:
Over the years I've had a few thermal fuses in houshold appliances go
open for no apparent reason. When I've replaced them with ones with the
same temperature rating they stayed working fine for years more.

A couple of days ago our three year old Bunn coffee maker quit, because
a 141 degree celcius overtemperature thermal fuse on the water tank
opened. It might possibly have happened because the water tank
thermostat stuck closed, but after I repaired it the thermostat cycled
just as it should.

I was suprised to find that there were TWO identical thermal fuses
connected in series located right next to each other, the bodies were
actually touching. That seemed like a belt and suspenders approach,
unless there's a significant likelihood that a thermal fuse won't open
when it should?

Comments?

Thanks guys,

Jeff


--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10e12 furlongs per fortnight.

Two fuses in series is pretty common. Always see this in microwave ovens and my wifes vacuum cleaner motor had two. Not sure if its belt and suspenders or just making it more likely to fail.

Jimmie

"jeff_wisnia" wrote in message
...
Over the years I've had a few thermal fuses in houshold appliances go
open for no apparent reason. When I've replaced them with ones with the
same temperature rating they stayed working fine for years more.

Way back when, my dad used to do forensic engineering - analyzing various
disaster scenes to determine the cause. Thermal switches and circuit
protectors (which were often referred to generically (and incorrectly) as
"Klixons" did indeed fail from time to time. Usually they failed "safe" and
would interrupt the current flow, but on occasion they would "weld"
themselves together and fail to break the circuit. That's why you'll see
two of them in series on devices capable of self-ignition like coffee
makers, electric furnaces, etc. The likelihood of one failing is small, but
not negligible. Regrettably, it's happened often enough that many
manufacturers now use two is series. The probability of both failing
simultaneously *should* be pretty astronomical.

I recall one case dad investigated where the Klixon (and it really *was* a
Klixon branded unit) failed because the thermostat of a large electric
furnace had been wired incorrectly and the Klixon was actually doing the
turning on and off of the unit (very dangerous situation!). The expert sent
by the Klixon Corporation to testify said that the constant cycling of the
protective device as a switch caused a premature failure. He believed the
unit in question had been cycled 1,000's of times before it welded itself in
the closed position. The Klixons had been subjected to a fire of over 1,200
degrees F (determined by the "alligatoring" of the wood beams and the color
of the burned copper wiring). The fire damage to the unit made precise
metallurgical determination of the failure rather difficult.

That's when I learned (30+ years ago) that circuit breakers should not be
used as control devices unless they are specifically rated for that type of
use. I believe most are, nowadays, but that's not always been the case. I
think we've had this discussion before with lots of different opinions.
IIRC, even those breakers labeled SWD (switch duty) are only meant for
low-frequency applications such as turning the lights off and on once a day.

Not sure what the NEC has to say about it - I would think they would require
a switch, other than a circuit breaker, to control a load. However, I do
recall a number of people saying they routinely used the breaker panel to
kill lights, etc. in large stores and shops but it seems odd to me not to
require a switch in the circuit outside the circuit panel. That makes me
assume that the practice is allowed, at least in some jurisdictions. Maybe
there's a low-frequency exception involving lighting loads in large
buildings when using SWD-rated breakers.

A far worse risk (and one that seems to be committed far more often) is
resetting a tripped circuit breaker over and over again. That's definitely
a no-no in terms of asking for the protective device to fail. The fourth
time our kitchen breaker tripped was the signal to me that I needed to
install more 20A lines (eventually 3) to the kitchen. Great SAF. The
kitchen breakers haven't tripped in years. Only the GFCI's have nuisance
tripped in that time.

--
Bobby G.