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Old 11th Dec 2011, 9:37 pm   #1
minor8hp
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Default Did mains dropper cables ever cause fires?

I'm working on a Champion, which has a cut off dropper cable. In the past, I've successfully rigged dropper cable sets for 115v. But.... the dropper cable had to drop from 240v to 80v at 0.15a. almost 25W.

If the mains cable was coiled up and a copy of the "Radio Times" was carelessly dropped on it. Could this have caused fires?
The dropper cable has whitish insulation, is this asbestos?
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Old 11th Dec 2011, 9:55 pm   #2
Simon Gittins
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Default Re: Did mains dropper cables ever cause fires?

I have heard them referred to as "curtain burners". They should run just warm to the touch when stretched out; they would get much hotter if coiled up. As you've guessed, they contain asbestos.
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Old 11th Dec 2011, 11:16 pm   #3
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Exclamation Re: Did mains dropper cables ever cause fires?

As a 10 year old I was given a lovely Champion set which had never been used & was still in its box with a picture of Arthur Askey on the front saying "its Champion"! This was the scarce 3 waveband Blue Bakelite one!
Anyway I had it working a treat in my bedroom until Dad spotted the mains wire getting warm. "No good", he said and insisted it was replaced with "Proper twin flex". Despite my howls of protest. Yes he did the deed and in doing so blew a large hole in the top of the radio, started a fire and filled my room with choking black soot & smoke. "See", he said "it was just about to go"
Dropper cords were dangerous but not as dangerous as some of the folks using the sets they were attached to!
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Old 11th Dec 2011, 11:29 pm   #4
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Default Re: Did mains dropper cables ever cause fires?

Maybe your dad should have heeded the warning on the back of the set, "on no account should the power cord be shortened".
I have a 1940's Portadyne midget set still running on it's original line cord dropper, it gets warm during use, but nothing too alarming, but it is never left on unattended

You could replace it with a capacitive dropper, or the set will probably work fine via 110V transformer.

Mark
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Old 11th Dec 2011, 11:46 pm   #5
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Default Re: Did mains dropper cables ever cause fires?

Quote:
Originally Posted by kalee99 View Post
Yes he did the deed and in doing so blew a large hole in the top of the radio, started a fire and filled my room with choking black soot & smoke. "See", he said "it was just about to go"
Paul your avitar says it all about the experience you had.

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Old 11th Dec 2011, 11:54 pm   #6
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Default Re: Did mains dropper cables ever cause fires?

I seem to remmember The Bill Smith Chronicles in the Radiophile talking about wrapping the line cord around your body as a source of heat. (I may have mis- remmembered but I am sure a Radiophile scholar will remmember the article to which I refer.)

I have a few sets using dropper cable and indeed in the 1980's there was still stocks of the stuff around and I replaced the cable on my Pilot little Maestro.

It gets warm rather than hot.

I also seem to remmember also that the method of finding a break in the dropper was poking a pin through the insulation till you localised the break.
I won't describe the rest of the process for fear of being censored

Enjoy

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Old 12th Dec 2011, 12:42 am   #7
kalee99
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Cool Re: Did mains dropper cables ever cause fires?

Quote:
Originally Posted by mark pirate View Post
Maybe your dad should have heeded the warning on the back of the set, "on no account should the power cord be shortened"
He did! The replacement flex was carefully measured out to within an 1/8" of the line cord
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Old 13th Dec 2011, 12:59 pm   #8
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Default Re: Did mains dropper cables ever cause fires?

I'm wanting to get my Little Maestro professionally overhauled, but everyone I talk to wants to fit something instead of the line dropper. Can anyone supply a suitable length of line, or, indeed, refurbish the set to the original spec.?
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Old 13th Dec 2011, 2:11 pm   #9
Peter.N.
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Default Re: Did mains dropper cables ever cause fires?

We used to get quite a number of line cord equipped sets in for repair, in fact we had several drums of Radiospares line cord of different resistances in stock, never heard of one causing a fire though, in fact if the cord was sensibly routed the heat would be disipated far more effectively than from a dropper inside a cabinet.

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Old 13th Dec 2011, 11:31 pm   #10
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Default Re: Did mains dropper cables ever cause fires?

I don't doubt that they did on occasion. I don't think though that they're inherently dangerous when used properly and looked after. As Peter's said, the actual heat dissipation is over such a wide area that it seems like it would be easily as safe as an integral dropper. I'm sure curtains draped over sets have caused enough problems in the past as well!

Problem is though that they're prone to damage by kinks, abrasion, moisture ingress, getting stepped on etc, or misuse (being used coiled up, stuffed in a drawer next to the set etc - or of course being shortened or replaced with standard flex!). Whereas a dropper resistor is pretty immune to these things being safely tucked away in the set itself.
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Old 14th Dec 2011, 1:07 pm   #11
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Default Re: Did mains dropper cables ever cause fires?

I'm inclined to think that they become dangerous through premature ageing. The rubber insulation seems to go flaky throughout the length, rather than just near the ends, and this, coupled with too high a fuse on the board, could be the cause of curtain fires.
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Old 14th Dec 2011, 11:18 pm   #12
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Default Re: Did mains dropper cables ever cause fires?

Personally I would not ever use a set with a line cord dropper, at least if a dropper resistor inside a radio set overheats it is contained inside the set

I am pretty sure that safety regulations nowadays would never permit such a system to be used mainly for the fact that users will inevitably coil them up.

Having said all that what's the difference between a line cord dropper and an electric blanket that most of us use on a daily basis in the winter?

Regards.

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Old 14th Dec 2011, 11:40 pm   #13
minor8hp
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Default Re: Did mains dropper cables ever cause fires?

I used to be involved in designing and testing IT equipment to the EC safety standard EN 60950.
These old radios with their live chassis etc wouldn't have made it through the test house door. By today's standards, they are dangerous...... But fun to work on!
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Old 14th Dec 2011, 11:48 pm   #14
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Default Re: Did mains dropper cables ever cause fires?

Hi.
I think we all realise that line dropping cord would not pass today's regulations, the same could also be said of the cars produced at the same time, they would never pass the crash tests now!
We still can drive old cars and there is no reason why we cannot listen to old radios. Undamaged line cord properly laid out is actually safer than an internal dropper. An internal dropper concentrates heat build up into a small area that can in certain instances cause a fire, an undamaged line cord runs much cooler as it not contained into a small area, it dissipates heat efficiently, it's only when someone decides to bung it under a carpet or alter it that the problems start.
I have no qualms about using a Radio with an undamaged line cord.
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Old 15th Dec 2011, 10:53 am   #15
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Default Re: Did mains dropper cables ever cause fires?

AFAIK line dropper cords would still be permitted today, not required for modern radios that use very low voltages from a power supply, probably switched mode.

One can still purchase flourescent inspection lamps that use a high resistance cord as a ballast resistance in series with a flourescent lamp.
The lamp voltage is about 60 volts, leaving about 180 volts accross the dropper cord, at about 0.16 amp.
These are still sold and are CE marked, and yes they come with a warning not to shorten, remove, or coil up the cord.

If anyone has a radio that uses 0.15 amp at a voltage less than mains, then it might be worth re-useing the line dropper cord from a flourescent light if the original is not serviceable.
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Old 15th Dec 2011, 5:54 pm   #16
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Default Re: Did mains dropper cables ever cause fires?

Interesting stuff Broadgage - will keep an eye open for this!

I have also got a thoery that type K thermocouple compensting cable could be used....
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Old 15th Dec 2011, 5:55 pm   #17
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Default Re: Did mains dropper cables ever cause fires?

The cable should be disposed of carefully as it contains white asbestos fibers which very easily become airbourne and can cause serious health problems. Some risks aren't worth taking...
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Old 16th Dec 2011, 10:30 am   #18
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Default Re: Did mains dropper cables ever cause fires?

I have just finished restoring this tiny General Electric GD-520 on which I had decided to leave the original line cord dropper, there is very little room to fit dropper caps. I had it on test on Wednesday evening (works very well now) running through a 110 volt transformer. When I returned to the set last night to give the volume pot a squirt, I discovered that the set was still connected (but switched off) and had been for 24 hours . No ill effects, but who knows what could have happened to that old line cord over that timespan .
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Old 31st Mar 2012, 11:36 pm   #19
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Default Re: Did mains dropper cables ever cause fires?

I've got a 1960s Chilean-made RCA radio.

It's a bog-standard 5-tube series-string "All American 5" circuit designed for 110-volts. To adapt it to the Chilean 220 volt service, the manufacturer fitted it with a dropper resistor cord that's about 5 feet long & wrapped in cloth.

The radio works (recapped) - and the cord does get quite warm with use. Not uncomfortable, though.

My mother was helping me pack up some radios for an upcoming move.

Being a child of the 50s and having grown up in Colombia, she had obviously never seen such a device. Colombia has a 110-volt service and by then nobody was making any 110-volt radios with dropper cords.

She thought it was funny that the radio used an "electric iron cord" as she called it.

When I explained it to her, she did remark that she thought that thing was a bit of a fire hazard. When time came to pack the radio, she did make sure not to hank it up tight like we often do to power cords (back & forth and then wrap aroud) when storing.
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Old 1st Apr 2012, 1:22 am   #20
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Default Re: Did mains dropper cables ever cause fires?

It's generally only a problem with American sets adapted for use on 220-240V supplies where this was done on the cheap. A resistive line cord is reasonably safe if used as intended, but given the general cluelessness of the population you will inevitably find people using the sets with the cord coiled up to save space or hidden under the carpet.

The small number of US sets commercially exported to Britain after WW2 don't use resistive line cords, but they are common with American midget sets exported in the 30s and particularly during WW2 under lend-lease.
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