Thermal Fuse, Transformer

[Stevie D]

I've a question as to which value 'fuse' to use in series with the
primary winding of this Technics amplifier of which the original one
opened-up. I bought two today and will wait to hear from this group
before I proceed. I've purchased a 171 degrees f and a 189 degrees f .
I suspect I might be a little off maybe, maybe too high??? I cannot
remove the original one to verify. Any help is appreciated, thank-you.
Cheers, Steve

[Eeyore]

Stevie D wrote:

> I've a question as to which value 'fuse' to use in series with the
> primary winding of this Technics amplifier of which the original one
> opened-up. I bought two today and will wait to hear from this group
> before I proceed. I've purchased a 171 degrees f and a 189 degrees f .
> I suspect I might be a little off maybe, maybe too high??? I cannot
> remove the original one to verify. Any help is appreciated, thank-you.

It's supposed to open before the winding and insulation temperatures
exceed a safe level.

Since 130C is an extra specially high option, yes you're way high. Oh it's
Fahrenheit. Convert it yourself. I can't be bothered with retarded US only
units. Get METRIC !

105C is more normal as a safe materials temp but the switch has to be in a
'hot spot', so a lower temp may be used in practice to compensate..

Graham

[Diogenes]

Eeyore wrote:
>
> Stevie D wrote:
>
>> I've a question as to which value 'fuse' to use in series with the
>> primary winding of this Technics amplifier of which the original one
>> opened-up. I bought two today and will wait to hear from this group
>> before I proceed. I've purchased a 171 degrees f and a 189 degrees f .
>> I suspect I might be a little off maybe, maybe too high??? I cannot
>> remove the original one to verify. Any help is appreciated, thank-you.
>
> It's supposed to open before the winding and insulation temperatures
> exceed a safe level.
>
> Since 130C is an extra specially high option, yes you're way high. Oh it's
> Fahrenheit. Convert it yourself. I can't be bothered with retarded US only
> units. Get METRIC !
>
> 105C is more normal as a safe materials temp but the switch has to be in a
> 'hot spot', so a lower temp may be used in practice to compensate..
>
> Graham
>
>
what a pompous ass. anything of value that you add is completely nulled
by your attitude.
plonk.

[Eeyore]

Diogenes wrote:

> Eeyore wrote:
> > Stevie D wrote:
> >
> >> I've a question as to which value 'fuse' to use in series with the
> >> primary winding of this Technics amplifier of which the original one
> >> opened-up. I bought two today and will wait to hear from this group
> >> before I proceed. I've purchased a 171 degrees f and a 189 degrees f .
> >> I suspect I might be a little off maybe, maybe too high??? I cannot
> >> remove the original one to verify. Any help is appreciated, thank-you.
> >
> > It's supposed to open before the winding and insulation temperatures
> > exceed a safe level.
> >
> > Since 130C is an extra specially high option, yes you're way high. Oh it's
> > Fahrenheit. Convert it yourself. I can't be bothered with retarded US only
> > units. Get METRIC !
> >
> > 105C is more normal as a safe materials temp but the switch has to be in a
> > 'hot spot', so a lower temp may be used in practice to compensate..
>
> what a pompous ass. anything of value that you add is completely nulled
> by your attitude.
> plonk.

Why do bloody Americans have to use units no-one ekse in the world does ?

Go **** yourself !

Fahrenheit ! LMAO.

[Eeyore]

Soundhaspriority wrote:

> "Stevie D" > wrote
>
> > I've a question as to which value 'fuse' to use in series with the
> > primary winding of this Technics amplifier of which the original one
> > opened-up. I bought two today and will wait to hear from this group
> > before I proceed. I've purchased a 171 degrees f and a 189 degrees f .
> > I suspect I might be a little off maybe, maybe too high??? I cannot
> > remove the original one to verify. Any help is appreciated, thank-you.
> > Cheers, Steve
>
> You partially unwound the transformer?
>
> I don't understand the rationale for thermal fuses in transformer primaries.

To stop them catching fire.


> Going back afew years, I don't recall they were used at all. Yamaha preamps
> transitioned from a design which used discrete external fuses to one that
> used the internal fuse.
>
> Is there anyone who can supply a detailed argument why the thermal fuse
> could not be omitted, replaced instead by a close-value external fuse?

Slightly complicated story w.r.t. power amps. I don't have time right now.


> It seems to me the purpose may have been to avoid the occasional spontaneous
> fuse blow, but when the internal one goes, what a mess it is!

What I did was to fit 'logic level' auto-resetting thermal switches in some
amps' transformers which simply muted the audio until they cooled down. Nothing
to replace.

Graham

[Arny Krueger]

"François Yves Le Gal" > wrote in
message

> On Sat, 22 Nov 2008 18:22:35 +0000, Eeyore
> > wrote:

>> Why do bloody Americans have to use units no-one ekse in
>> the world does ?

> Because they want to see some nice fireworks when their
> silly space shuttle explodes.

....as opposed to the rest of the world who doesn't have anything operating
that is even close to a space shuttle, and all but one of them never even
ever tried.

This is like me making fun of my neighbor because his Ferrari has a flat
tire.

[Trevor Wilson[_2_]]

"Soundhaspriority" > wrote in message
...
>
> "Stevie D" > wrote in message
> ...
>> I've a question as to which value 'fuse' to use in series with the
>> primary winding of this Technics amplifier of which the original one
>> opened-up. I bought two today and will wait to hear from this group
>> before I proceed. I've purchased a 171 degrees f and a 189 degrees f .
>> I suspect I might be a little off maybe, maybe too high??? I cannot
>> remove the original one to verify. Any help is appreciated, thank-you.
>> Cheers, Steve
>
> You partially unwound the transformer?
>
> I don't understand the rationale for thermal fuses in transformer
> primaries. Going back afew years, I don't recall they were used at all.
> Yamaha preamps transitioned from a design which used discrete external
> fuses to one that used the internal fuse.
>
> Is there anyone who can supply a detailed argument why the thermal fuse
> could not be omitted, replaced instead by a close-value external fuse? It
> seems to me the purpose may have been to avoid the occasional spontaneous
> fuse blow, but when the internal one goes, what a mess it is!

**[True story]
----
Many years ago (ca. 1985), I sold a range of audio equipment, from a range
of manufacturers, including Sansui. I refused to sell some of the Sansui
products, because I did not like the construction, which consisted of
plastic side pieces and a pressboard baseplate. The power transformer was
mounted within 1cm of the plastic side cheeks. Typical models included:
A700, A900, B77, et al. I did sell the AUD series, due to their high quality
construction and advanced topology.

A mate called into my store one day and asked for me. I wasn't available, so
he travelled to another store. The other store sold him some of the Sansui
stuff, I refused to sell. A couple of years later I ran into him at a
function. I asked him how he was going with his house rebuilding. He said
that things were progressing. I asked if the investigators had worked out
what had caused the fire that burned his house down. He said that it was the
stereo amplifier that did it.
----
It was not uncommon back then (ca. 1985) for repairers to short out the
thermal fuse, after it had failed (which it did with huge numbers of cheap
Sansui amps, due to the high operating temps of the transformers - partly
due to the poor quality of the transformers and partly due to poor
ventilation, due the pressboard baseplates).

Moral: Always replace the thermal fuse with another, similar thermal fuse.

Further and for the record: So cheap and crappy were this range of
amplifiers, that Sansui employed *no* current limiters in many of the models
in their cheap range.


--
Trevor Wilson
www.rageaudio.com.au

[Chris Hornbeck]

On Sun, 23 Nov 2008 02:02:24 -0500, "Soundhaspriority"
> wrote:

>I don't understand the rationale for thermal fuses in transformer primaries.
>Going back afew years, I don't recall they were used at all. Yamaha preamps
>transitioned from a design which used discrete external fuses to one that
>used the internal fuse.
>
>Is there anyone who can supply a detailed argument why the thermal fuse
>could not be omitted, replaced instead by a close-value external fuse? It
>seems to me the purpose may have been to avoid the occasional spontaneous
>fuse blow, but when the internal one goes, what a mess it is!

It's almost certainly a defacto requirement for UL type approval. For
the manufacturer, an internal thermal fuse adds a very large warranty
repair cost (a whole power transformer) to any of gazillions of
possible electronic failures, so would be avoided if it were possible
to do so.

Much thanks, as always,
Chris Hornbeck

[Eeyore]

Chris Hornbeck wrote:

> "Soundhaspriority" > wrote:
>
> >I don't understand the rationale for thermal fuses in transformer primaries.
> >Going back afew years, I don't recall they were used at all. Yamaha preamps
> >transitioned from a design which used discrete external fuses to one that
> >used the internal fuse.
> >
> >Is there anyone who can supply a detailed argument why the thermal fuse
> >could not be omitted, replaced instead by a close-value external fuse? It
> >seems to me the purpose may have been to avoid the occasional spontaneous
> >fuse blow, but when the internal one goes, what a mess it is!
>
> It's almost certainly a defacto requirement for UL type approval.

UL doesn't count much any more. Except in ONE country.

Apply the tests in IEC60950 and you'll understand.


> For the manufacturer, an internal thermal fuse adds a very large warranty
> repair cost (a whole power transformer) to any of gazillions of
> possible electronic failures, so would be avoided if it were possible
> to do so.

They do it because doing it better is more expensive. One cost more than cancels
the other.

Graham

[GregS[_3_]]

In article >, Stevie D > wrote:
>I've a question as to which value 'fuse' to use in series with the
>primary winding of this Technics amplifier of which the original one
>opened-up. I bought two today and will wait to hear from this group
>before I proceed. I've purchased a 171 degrees f and a 189 degrees f .
>I suspect I might be a little off maybe, maybe too high??? I cannot
>remove the original one to verify. Any help is appreciated, thank-you.
>Cheers, Steve

Just bypass it. If it overheated correct the possible problem by installing a fan.
You can still use a thermal fuse. Its unknown why they melted, but
probably from hitting them too hard. Most transformers
opperate and you are able to touch them, so use a fuse no higher than 130 degrees,
thats on the outside of the case. Your not going to be able to get
inside the windings very far. I don't know todays standards. Does every transformer require a fuse,
or only those underdesigned.

greg

[Eeyore]

GregS wrote:

> Stevie D > wrote:
> >I've a question as to which value 'fuse' to use in series with the
> >primary winding of this Technics amplifier of which the original one
> >opened-up. I bought two today and will wait to hear from this group
> >before I proceed. I've purchased a 171 degrees f and a 189 degrees f .
> >I suspect I might be a little off maybe, maybe too high??? I cannot
> >remove the original one to verify. Any help is appreciated, thank-you.
> >Cheers, Steve
>
> Just bypass it. If it overheated correct the possible problem by installing a fan.
> You can still use a thermal fuse. Its unknown why they melted, but
> probably from hitting them too hard. Most transformers
> opperate and you are able to touch them, so use a fuse no higher than 130 degrees,
> thats on the outside of the case. Your not going to be able to get
> inside the windings very far. I don't know todays standards. Does every transformer require a fuse,
> or only those underdesigned.

Every transformer needs to be protected from a short on the output. Small transformers may have such high DC winding resistance
that differentiating between a shorted output and normal operation (especially switch-on surge) is very difficult, so using a
'normal fuse' is tricky. Hence the thermal fuse.

Graham

[Trevor Wilson[_2_]]

"GregS" > wrote in message
...
> In article
> >,
> Stevie D > wrote:
>>I've a question as to which value 'fuse' to use in series with the
>>primary winding of this Technics amplifier of which the original one
>>opened-up. I bought two today and will wait to hear from this group
>>before I proceed. I've purchased a 171 degrees f and a 189 degrees f .
>>I suspect I might be a little off maybe, maybe too high??? I cannot
>>remove the original one to verify. Any help is appreciated, thank-you.
>>Cheers, Steve
>
> Just bypass it. If it overheated correct the possible problem by
> installing a fan.
> You can still use a thermal fuse. Its unknown why they melted, but
> probably from hitting them too hard. Most transformers
> opperate and you are able to touch them, so use a fuse no higher than 130
> degrees,
> thats on the outside of the case. Your not going to be able to get
> inside the windings very far. I don't know todays standards. Does every
> transformer require a fuse,
> or only those underdesigned.

**Read my earlier post. Lazy techs who bypass protection systems can cause
serious damage to not only the equipment concerned.


--
Trevor Wilson
www.rageaudio.com.au

[Chris Hornbeck]

On Mon, 24 Nov 2008 14:21:01 GMT, (GregS)
wrote:

>Just bypass it.

Please, please don't do this.

Thank you,
Chris Hornbeck

[Eeyore]

Chris Hornbeck wrote:

> (GregS) wrote:
>
> >Just bypass it.
>
> Please, please don't do this.

I dunno. Some people enjoy fires !

Graham

[Richard Crowley]

"Stevie D" wrote ...
> I've a question as to which value 'fuse' to use in series with the
> primary winding of this Technics amplifier of which the original one
> opened-up. I bought two today and will wait to hear from this group
> before I proceed. I've purchased a 171 degrees f and a 189 degrees f .
> I suspect I might be a little off maybe, maybe too high??? I cannot
> remove the original one to verify. Any help is appreciated, thank-you.
> Cheers, Steve

So, install the 171 and stress-test the system to see if it will hold.
If it gets too hot and cuts out, put in the 189. If that one also gets
too hot and cuts out, then the problem might be with the transformer
and not with the thermal fuses.

[Eeyore]

Richard Crowley wrote:

> "Stevie D" wrote ...
> > I've a question as to which value 'fuse' to use in series with the
> > primary winding of this Technics amplifier of which the original one
> > opened-up. I bought two today and will wait to hear from this group
> > before I proceed. I've purchased a 171 degrees f and a 189 degrees f .
> > I suspect I might be a little off maybe, maybe too high??? I cannot
> > remove the original one to verify. Any help is appreciated, thank-you.
> > Cheers, Steve
>
> So, install the 171 and stress-test the system to see if it will hold.
> If it gets too hot and cuts out, put in the 189. If that one also gets
> too hot and cuts out, then the problem might be with the transformer
> and not with the thermal fuses.

Or the PRODUCT !

Graham

[Stevie D]

On Nov 24, 7:10*pm, Chris Hornbeck >
wrote:
> On Mon, 24 Nov 2008 14:21:01 GMT, (GregS)
> wrote:
>
> >Just bypass it.
>
> Please, please don't do this.
>
> Thank you,
> Chris Hornbeck

Thanks all for the advise. Here's what I've done; replaced with the
171 degrees f thermal fuse, let it sit, turned on with volume at zero
and waited... It took a few hours, then I touched the transformer, it
was hot to the touch, hot enough to worry me. I turned the receiver
off and waited two hours. The xfmr was still warm. Under "power on"
condition, it was almost unbearable to keep my hand on it, this is my
litmus test, and I considered it a fail! The fuse held up but my
customer is not getting this back until I undo my repair and recommend
he buy a new one.
Cheers

[GregS[_3_]]

In article >, "Soundhaspriority" > wrote:
>
>"Chris Hornbeck" > wrote in message
...
>> On Sun, 23 Nov 2008 02:02:24 -0500, "Soundhaspriority"
>> > wrote:
>>
>>>I don't understand the rationale for thermal fuses in transformer
>>>primaries.
>>>Going back afew years, I don't recall they were used at all. Yamaha
>>>preamps
>>>transitioned from a design which used discrete external fuses to one that
>>>used the internal fuse.
>>>
>>>Is there anyone who can supply a detailed argument why the thermal fuse
>>>could not be omitted, replaced instead by a close-value external fuse? It
>>>seems to me the purpose may have been to avoid the occasional spontaneous
>>>fuse blow, but when the internal one goes, what a mess it is!
>>
>> It's almost certainly a defacto requirement for UL type approval. For
>> the manufacturer, an internal thermal fuse adds a very large warranty
>> repair cost (a whole power transformer) to any of gazillions of
>> possible electronic failures, so would be avoided if it were possible
>> to do so.
>>
>You may be right, but I wonder if there are other factors involved as well?
>What if the transformer is enclosed in metal? What if the transformer metal
>can sink enough power such that it could not reach sustained ignition with a
>proper slow-blo fuse in place? It seems to me this was the strategy in older
>equipment.
>
>Does anyone know when thermal fuses came in? The earliest piece of equipment
>I have seen that was junked because of thermal fuse failure was a Yamaha
>C-70 preamp. I have several of these; the one that failed had no fuse
>external to the power transformer. The others did.

If equipment has an on/off switch it certainly should have a fuse.
I would have thought these modern amplifiers that can't drive
4 ohms should certaily have a thermal fuse.

greg

[Eeyore]

Stevie D wrote:

> Chris Hornbeck > wrote:
> (GregS) wrote:
> >
> > >Just bypass it.
> >
> > Please, please don't do this.
>
> Thanks all for the advise. Here's what I've done; replaced with the
> 171 degrees f thermal fuse, let it sit, turned on with volume at zero
> and waited... It took a few hours, then I touched the transformer, it
> was hot to the touch, hot enough to worry me. I turned the receiver
> off and waited two hours. The xfmr was still warm. Under "power on"
> condition, it was almost unbearable to keep my hand on it, this is my
> litmus test, and I considered it a fail! The fuse held up but my
> customer is not getting this back until I undo my repair and recommend
> he buy a new one.

Sounds like a shorted turn to me.

Graham

[Eeyore]

GregS wrote:

> If equipment has an on/off switch it certainly should have a fuse.

Not a requirement (for a replaceable fuse) at all. Merely enough protection to prevent fire hazard.

Graham

[GregS[_3_]]

In article >, Eeyore > wrote:
>
>
>GregS wrote:
>
>> If equipment has an on/off switch it certainly should have a fuse.
>
>Not a requirement (for a replaceable fuse) at all. Merely enough protection to
> prevent fire hazard.
>
>Graham

My feeling, switches frequently go bad, fall apart, and
touch chassis and sparks, and, or shock. The fuse can't
protect for shock though. There are wires which usually
can't handle full outlet power after entering the equipment, plus the line
cord often is only 18 gauge. Thats why you need a fuse.

But my Christmas tree lights and a lot of other things don't seem to have a fuse.


greg

[Eeyore]

GregS wrote:

> Eeyore > wrote:
> >GregS wrote:
> >
> >> If equipment has an on/off switch it certainly should have a fuse.
> >
> >Not a requirement (for a replaceable fuse) at all. Merely enough protection to
> > prevent fire hazard.
>
> My feeling, switches frequently go bad, fall apart, and
> touch chassis and sparks, and, or shock.

In which case they are unapproved for mains use.


> The fuse can't protect for shock though.

It's not meant to.


> There are wires which usually
> can't handle full outlet power after entering the equipment, plus the line
> cord often is only 18 gauge. Thats why you need a fuse.

To protect the cable. Correct. A little known fact.


> But my Christmas tree lights and a lot of other things don't seem to have a fuse.

In the UK we uniquely have a fuse inside the AC wall plug.
http://en.wikipedia.org/wiki/BS_1363

The fuse can be selected to suit the cable rating. One of many reasons why electrical fires are
virtually unknown here.

Graham

[Mark D. Zacharias[_3_]]

"Stevie D" > wrote in message
...
On Nov 24, 7:10 pm, Chris Hornbeck >
wrote:
> On Mon, 24 Nov 2008 14:21:01 GMT, (GregS)
> wrote:
>
> >Just bypass it.
>
> Please, please don't do this.
>
> Thank you,
> Chris Hornbeck

>Thanks all for the advise. Here's what I've done; replaced with the
>171 degrees f thermal fuse, let it sit, turned on with volume at zero
>and waited... It took a few hours, then I touched the transformer, it
>was hot to the touch, hot enough to worry me. I turned the receiver
>off and waited two hours. The xfmr was still warm. Under "power on"
>condition, it was almost unbearable to keep my hand on it, this is my
>litmus test, and I considered it a fail! The fuse held up but my
>customer is not getting this back until I undo my repair and recommend
>he buy a new one.
>Cheers

If it's getting that hot just sitting there turned on, it has some other
problem. A shorted diode in the power supply area for example. A voltage
regulator could be sitting there happily putting out 12 volts DC even with a
large AC component going in. You might never hear it or trigger the
protection circuit, but the transformer would get hot like that.

Actually had this happen once, in fact.

Mark Z.

[Tomi Holger Engdahl]

Eeyore > writes:

> > But my Christmas tree lights and a lot of other things don't seem to have a fuse.
>
> In the UK we uniquely have a fuse inside the AC wall plug.
> http://en.wikipedia.org/wiki/BS_1363
>
> The fuse can be selected to suit the cable rating. One of many reasons why electrical fires are
> virtually unknown here.

Ring circuits are commonly used in British wiring with fused 13 A
plugs to BS 1363. They are generally wired with 2.5 mm² cable and
protected by a 30 A fuse, an older 30 A circuit breaker, or a European
harmonised 32 A circuit breaker.

When such high current main ring circuits are used , it is definately
necessary to have a smaller size fuze on the mains plug (sized to
prptect the plug wire). If 30A or more gets directly to thin
wire it will definatly start to melt soon...

In other part of Europe the mains outlets are normally fused with
10A or 16A fuses (maybe 6A on some very old systems). The
thickness of the mains cable on the equipment is sized so
that in can safely carry the equipment normal operating current
plus that a short circuit on that cable will burn the 16A fuse
long before the wire insulation starts to melt. The fuse
or other protection in equipment will make sure that the
constant current flow equipment can take on cable will
not exceed the wire constant current flow rating.
So equipment fusing protects against constant overload
possibility and wire is thick enough to burn fuse
quickly on short circuit without too much damage.
The equipment cables have normally thickness of
0.75mm^2 to 1.5mm^2 on normal equipment plugged
to 10A or 16A outlets (there are some special exceptions
where even thinner cable is allowed).

Electrical fires are also quite rare where I live
(I live in Finland).

--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/

[Tomi Holger Engdahl]

(GregS) writes:

> In article >, Eeyore > wrote:
> >
> >
> >GregS wrote:
> >
> >> If equipment has an on/off switch it certainly should have a fuse.
> >
> >Not a requirement (for a replaceable fuse) at all. Merely enough protection to
> > prevent fire hazard.
> >
> >Graham
>
> My feeling, switches frequently go bad,

Sometimes yes.

> fall apart, and

Sometimes when mechanically abused.

> touch chassis and sparks, and, or shock.

Touchning chassis or socking the user is pretty
hard on the equipment where the switches are
made of insulating plastic. The switch can
internally be damaged pretty baddly without
any danger to user when switch is made of
plastic material and wires to it mounted
so that they can't easy get loose. That's
the norm in normal modern equipment where I live.
It is not recommended to use switches with
metal case and metal handle for equipment
mains power switching.

Danger of shock user or mains power toucing
the case is petty much closer on the switches
with user touchable metal parts unless the
switch is very very carefully designed.
In many metallic switches I have see that have
been rated for up 125V mains voltage there
is not to much safety marginal if something
breaks down inside switch... Dangerous sparking,
touching case or getting shocked are possible.

> The fuse can't protect for shock though.

Fuses usually don't protect the user if they get in
touch with the mains power...

> There are wires which usually
> can't handle full outlet power after entering the equipment, plus the line
> cord often is only 18 gauge. Thats why you need a fuse.
>
> But my Christmas tree lights and a lot of other things
> don't seem to have a fuse.

Many simple lighting equipment do not use fuses, because
there is very low possiblity that the device starts
to take more power than wire is rated... The light bulb
itself mostly acts more or less like a fuse prtecting
against too mugh currents..

--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/

[GregS[_3_]]

In article >, "Mark D. Zacharias" > wrote:
>
>"Stevie D" > wrote in message
...
>On Nov 24, 7:10 pm, Chris Hornbeck >
>wrote:
>> On Mon, 24 Nov 2008 14:21:01 GMT, (GregS)
>> wrote:
>>
>> >Just bypass it.
>>
>> Please, please don't do this.
>>
>> Thank you,
>> Chris Hornbeck
>
>>Thanks all for the advise. Here's what I've done; replaced with the
>>171 degrees f thermal fuse, let it sit, turned on with volume at zero
>>and waited... It took a few hours, then I touched the transformer, it
>>was hot to the touch, hot enough to worry me. I turned the receiver
>>off and waited two hours. The xfmr was still warm. Under "power on"
>>condition, it was almost unbearable to keep my hand on it, this is my
>>litmus test, and I considered it a fail! The fuse held up but my
>>customer is not getting this back until I undo my repair and recommend
>>he buy a new one.
>>Cheers
>
>If it's getting that hot just sitting there turned on, it has some other
>problem. A shorted diode in the power supply area for example. A voltage
>regulator could be sitting there happily putting out 12 volts DC even with a
>large AC component going in. You might never hear it or trigger the
>protection circuit, but the transformer would get hot like that.
>
>Actually had this happen once, in fact.
>
>Mark Z.

I have seen bad transformers with high loss such as a shorted turn.
When the transformer overheated the short may have appeared
or it may have just decided to short for no other reason.

greg

[Trevor Wilson[_2_]]

"GregS" > wrote in message
...
> In article >, Eeyore
> > wrote:
>>
>>
>>GregS wrote:
>>
>>> If equipment has an on/off switch it certainly should have a fuse.
>>
>>Not a requirement (for a replaceable fuse) at all. Merely enough
>>protection to
>> prevent fire hazard.
>>
>>Graham
>
> My feeling, switches frequently go bad, fall apart, and
> touch chassis and sparks, and, or shock. The fuse can't
> protect for shock though. There are wires which usually
> can't handle full outlet power after entering the equipment, plus the line
> cord often is only 18 gauge. Thats why you need a fuse.

**No. That is why you need either an Earthed chassis, or double insulation.
One of these is mandatory over most of the planet.

>
> But my Christmas tree lights and a lot of other things don't seem to have
> a fuse.

**And they would need to be double insulated in most nations. You must have
very old Christmas tree lights. Perhaps such dangerous products are still
legally available in the US. I've not seen anything but low Voltage types
for many years.


--
Trevor Wilson
www.rageaudio.com.au

[Jerry Peters]

Trevor Wilson > wrote:
>
>
>
> "GregS" > wrote in message
> ...
>> In article >, Eeyore
>> > wrote:
>>>
>>>
>>>GregS wrote:
>>>
>>>> If equipment has an on/off switch it certainly should have a fuse.
>>>
>>>Not a requirement (for a replaceable fuse) at all. Merely enough
>>>protection to
>>> prevent fire hazard.
>>>
>>>Graham
>>
>> My feeling, switches frequently go bad, fall apart, and
>> touch chassis and sparks, and, or shock. The fuse can't
>> protect for shock though. There are wires which usually
>> can't handle full outlet power after entering the equipment, plus the line
>> cord often is only 18 gauge. Thats why you need a fuse.
>
> **No. That is why you need either an Earthed chassis, or double insulation.
> One of these is mandatory over most of the planet.
>
>>
>> But my Christmas tree lights and a lot of other things don't seem to have
>> a fuse.
>
> **And they would need to be double insulated in most nations. You must have
> very old Christmas tree lights. Perhaps such dangerous products are still
> legally available in the US. I've not seen anything but low Voltage types
> for many years.

Some older Christmas tree lights used to have a replaceable fuse in
the plug. I'd expect more modern ones to have a non-replaceable fuse,
since if they ever short out you'd probably just pitch them.

Jerry