Copper wire instead of fuses?

[Gareth Magennis]

Here's something I've not seen before.

A Power Amplifier has binding posts which you are supposed to solder wire
between, instead of fuses.
This is on the low voltage power supply. The wire fuses go to the bridge
rectifier/10,000uF caps, and supply the +/- 15v supplies.

The PCB is inscribed "wire Cu 0.25mm" and also designated F2 and F3.

And yes, there is (or was) thin copper wire soldered in place on both
identical channels of this amp.
(One side has melted both these wire fuses, as the caps are bad)



Why would a manufacturer do this? I'd be inclined to put back wire ended
fuses.


I'm guessing 0.25mm means 0.25mm Cross Sectional Area rather than diameter,
but it is not clear.
The following table gives 6A and 15A for each possibility, which seems quite
high for a low voltage supply.
http://www.gxk.org.uk/info/wire.htm

I took out a small remaining piece of the wire and it actually measured just
below 0.5mm diameter, but this is not a reliable measurement as the wire has
obviously suffered trauma.






This is the amplifier in question:
http://www.kv2audio.com/products/esr-series/esr2800.html



Cheers,


Gareth.

[N_Cook]

I thought they'd been going the other way these days for elfin safety,
statutory specification of sand filled fuse barrels and not air for
mains ones anyway.
Its not that much different to the deliberate necking of pcb power rail
traces, to make sure any burn-ups occur in safeish areas, but how they
guaranteee non-flamability of the underlaying polyester or overlaying
conformal coating is a mystery still.

[Reinhard Zwirner]

Gareth Magennis schrieb:

> Here's something I've not seen before.
>
> A Power Amplifier has binding posts which you are supposed to solder

> wire between, instead of fuses. ...

Hi,

Metrix, a French manufacturer of multimeters, used this method (at
least) in MX202 multimeter series.

<http://public.beuth-hochschule.de/hamann/telefon/mx202.html>

Best regards

Reinhard

[John-Del]

Wow, talk about rekindling a memory I'm sure would have laid dormant until I died.

Back in the 60s, a couple of TV manufacturers used fusible links to protect the filament string. I don't remember the diameter only that we had a small roll of enameled wire of the correct diameter just for this purpose. A suitable size was cut, tinned, sleeved with a fabric tube and soldered between two terminals.

I don't recall why this was done as opposed to using a glass pigtail fuse or socketed fuse for that matter.

[hrho...@att.net]

Back in the 60s, a couple of TV manufacturers used fusible links to protect the filament string. I don't remember the diameter only that we had a small roll of enameled wire of the correct diameter just for this purpose. A suitable size was cut, tinned, sleeved with a fabric tube and soldered between two terminals.

I don't recall why this was done as opposed to using a glass pigtail fuse or socketed fuse for that matter.

Any recollection of which manufacturers used that method of fusing?

[Paul Drahn]

The reason is the circuit has a BIG inrush current. A regular fuse
material takes a bit of time to open, but if the current is below, but
close to the rated current, the fuse material will soften and sag, and
get thinner after many uses. A copper wire will not do this, but will
melt at the rated current you found.

My plant uses three 200 amp services with meters. They are fused for 200
amps with silver fuses. They do blow at a small percent above 200 amps
and almost instantly, and cost $75 each to replace.

Paul

[John-Del]

Snort... "recollection"? I wear a name tag so I remember who I am. But I KNOW my older brother will remember not only who used it but what gauge of wire as well. I'll post back later today.

[legg]

It's a cost and marketing consideration.

This product doesn't carry UL safety listing, so the issue of fuse
behaviour under single-fault abnormals may never have been raised. As
it is in low voltage circuitry, the issue may never have been raised.

The use of wire fuses, even when considered acceptible, required
dedicate hardware and specific wire manufactured for that purpose in
potentially hazardous applications. This application represents an
energy hazard, rather than a shock hazard. Low voltage fuses with DC
ratings are expensive, but do exist.

RL

[Ron D.]

I remember TV's with the wire method too. They almost always were routed out under the wire. I would guess that the typical user does not own a soldering iron.

[hrho...@att.net]

I have seen some Christmas light strings that have a copper wire in the plug in place of the more common regular miniature fuses that 95% of the manufacturers use. Can only tell if you take the plug apart with pliers and hammer, and that is the end of the whole plug assembly, so obviously a one-time event.

[John-Del]

I talked to my brother yesterday and while he remembers the wire fuse, he doesn't remember the manufacturer(s) either. He thinks it was used as line or B+ while I think it was filament protection. Just too long ago.

If Lenny is looking in, maybe he will remember.

[legg]

On Mon, 14 Mar 2016 06:41:43 -0700 (PDT), John-Del <ohg...@aol.com>
wrote:

Wire fuses were used in old mains fuse boxes, where wire was located
between screw-down terminals in a removable shielded plug assembly,
with isolated finger pull tabs. Basically a fuse assembly with
replaceable fuse link. Too easily defeated or misapplied with
non-standard fuse wire, and a source of combustion.

You can still buy "fuse wire" in the UK. Google it.

RL

[Cydrome Leader]

Gareth Magennis <soundser...@outlook.com> wrote:
> Here's something I've not seen before.
>
> A Power Amplifier has binding posts which you are supposed to solder wire
> between, instead of fuses.
> This is on the low voltage power supply. The wire fuses go to the bridge
> rectifier/10,000uF caps, and supply the +/- 15v supplies.
>
> The PCB is inscribed "wire Cu 0.25mm" and also designated F2 and F3.
>
> And yes, there is (or was) thin copper wire soldered in place on both
> identical channels of this amp.
> (One side has melted both these wire fuses, as the caps are bad)
>
>
>
> Why would a manufacturer do this? I'd be inclined to put back wire ended
> fuses.

Fusible links handle surge currents better than fuses.

My question is why is on the output of the transformer. Is the input
fused at all?

[Phil Allison]

Cydrome Leader wrote:
>
>
> My question is why is on the output of the transformer. Is the input
> fused at all?
>

** The two on/off switch incorporate circuit breakers, but the trannys are very large and the low voltage windings need protecting against an overload or short that would not trip the breakers.



.... Phil

[Cydrome Leader]

I've been thinking about this and can only conclude the fusible links are
to protect against further damage from someobdy recycling the input
breaker on a permanent fault. It doesn't really explain what the breaker
is protecting against though. You could continue to flip the
breaker/switch if the primary winding have a fault or short of some type.
Is this device graceful enough to just trip the breaker instead of burning
up in the case of an overload?

It's just a power amp so it's not like it needs to continue to run a
cooling fan or something like that in case of other failures in the
system.

Strange.

[Phil Allison]

Cydrome Leader wrote:

>
> >>
> >> My question is why is on the output of the transformer. Is the input
> >> fused at all?
> >>
> >
> > ** The two on/off switch incorporate circuit breakers,
> > but the trannys are very large and the low voltage windings
> > need protecting against an overload or short that would not
> trip the breakers.
>
>
> I've been thinking about this and can only conclude the fusible links are
> to protect against further damage from someobdy recycling the input
> breaker on a permanent fault.
>

** No, the breaker/switch would never react to a fault in the low voltage supply.

> doesn't really explain what the breaker
> is protecting against though.
>

** A major fault of course - one that would burn the transformer.



.... Phil

[Cydrome Leader]

Phil Allison <palli...@gmail.com> wrote:
> Cydrome Leader wrote:
>
>>
>> >>
>> >> My question is why is on the output of the transformer. Is the input
>> >> fused at all?
>> >>
>> >
>> > ** The two on/off switch incorporate circuit breakers,
>> > but the trannys are very large and the low voltage windings
>> > need protecting against an overload or short that would not
>> trip the breakers.
>>
>>
>> I've been thinking about this and can only conclude the fusible links are
>> to protect against further damage from someobdy recycling the input
>> breaker on a permanent fault.
>>
>
> ** No, the breaker/switch would never react to a fault in the low voltage supply.

You're right. I re-read and saw it's for the +/- 15 rails. Still not
really sure why a fuse there would not suffice though. The parts did their
job so they did work as designed.

>> doesn't really explain what the breaker
>> is protecting against though.
>>
>
>
> ** A major fault of course - one that would burn the transformer.

yup.

[Phil Allison]

Cydrome Leader wrote:


>
> You're right. I re-read and saw it's for the +/- 15 rails. Still not
> really sure why a fuse there would not suffice though.
>

** Looks to me like the unit has no easily replaced fuses - probably a good idea both for reliability and to avoid over hazardous fusing by amateurs.


.... Phil