Copper wire instead of fuses?

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.

Gareth Magennis schrieb:

Hi,

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

Best regards

Reinhard

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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 sma ll 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 betw een two terminals.

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

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 sma ll 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 betw een two terminals.

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

Any recollection of which manufacturers used that method of fusing?

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

ct the filament string. I don't remember the diameter only that we had a s mall 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 be tween two terminals.

or socketed fuse for that matter.

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

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

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.

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

tect 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.

se or socketed fuse for that matter.

KNOW my older brother will remember not only who used it but what gauge of wire as well. I'll post back later today.

I talked to my brother yesterday and while he remembers the wire fuse, he d oesn'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.

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

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?

** 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

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.

** No, the breaker/switch would never react to a fault in the low voltage supply. ** A major fault of course - one that would burn the transformer.

.... Phil

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.

yup.

** 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