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    • CommentAuthorRex
    • CommentTimeDec 20th 2019
     
    What ho one and all,

    Unfortunately, not directly a 'self build' question, but I hope the greater knowledge will be able to point me in the right direction.

    In the past, I had a secondary income from photography and have a old(ish) studio flash pack with three lights. The pack is basically a floor standing capacitor. have been asked to do some portraits after Christmas so thought I would check out the gear.

    Unfortunately over the years, (and lack of use) the cables from the flash heads have become so brittle that they are crumbling.

    The plan is to replace them but am having difficulty finding the right stuff. The cable is six core and has an outer diameter of 11mm. Each core has an insulated diameter of 3mm so I assume the copper is around 2.5mm2? Since it needs to be flexible, I assume the original is some kind of rubber covered.

    The attached photo give an idea of what I am after but am having no joy to date.

    Grateful for any ideas as I hardly even know what to ask for.

    Thanks, toodle pip and Merry Christams
      Flash Cable.jpg
    •  
      CommentAuthordjh
    • CommentTimeDec 20th 2019 edited
     
    RS components is probably a good place to start looking https://uk.rs-online.com/web/c/cables-wires/electrical-power-industrial-cable/multicore-industrial-cable/?rpp=100

    It would be a good idea to try to measure the core diameter more accurately and also determine what type of cable it is - solid or multi-core etc.

    Having said that, it seems quite likely to me that other components may have died as well, particularly capacitors, so it might be simpler to buy another unit or make alternative plans.

    PS I just threw out (to the recycling centre) three old computers. The ten year old one failed to boot. The twenty year old one failed to boot. I didn't even try to boot the thirty year old one! So it was back to my trusty sledgehammer to 'erase' the disks. Surprisingly hard work.
    • CommentAuthorRex
    • CommentTimeDec 20th 2019
     
    Thanks for your reply.

    Last time I used the units and power pack, there was no problem. These days, not possible to replace as technology has moved on considerably. The basic principle is the same, but .............!

    The way these things work, the capacitor delivers a very large bang to the flash tube so the cable probably needs to be around 2.5mm. It is not solid but does need to be flexible.

    Getting 6 core with an overall diameter of 11mm is an issue. Have found 7 core at around 11.5mm diameter and 2.5mm cross section but to date, have to buy 100 meters when i only need around 12m.
  1.  
    Use 3 parallel lengths of twin core and earth, one length running to each flash head? Twin core flex is readily available in lots of lengths, and different thicknesses for immersion heaters or lamps.
    Can't be sure from the pic but looks like that head is connected to three of the cores, including one that might be an earth.

    NB cable is often sold by cross-section area of its conductors, rather than by diameter. 2.5mm2 area cable (the stuff sockets are wired with) is not the same as 2.5mm diameter...

    Edit to add: big capacitors have their own hazards, better get hands-on help if you're unsure?
    • CommentAuthorRex
    • CommentTimeDec 20th 2019
     
    Certainly 3 x 2c+e would be a solution but somewhat unwieldy. 2.5mm or 2.5mm2 is confusing me. I have measured the existing cable, and the outer of the whole is 11mm diameter, but have no idea what the mm2 of the actual wires could be.

    All six of the cores are used. When it is up and running, there is a tungsten modelling lamp, so that would be 2 of the cores. The photo does not show the flash tube itself, but another 2 go to it; probably the yellow and black at the top of the photo, which are actually sheathed with extra insulation.

    I have found this https://www.elandcables.com/cables/h07rn-f-bs-en-50525-2-21-flexible-rubber-cable# which is available as 7 core, 2.5mm2 but the diameter is too large. Somewhere I saved a link to another 7c which is around 12mm diameter.
    • CommentAuthorMatBlack
    • CommentTimeDec 20th 2019
     
    It might be worth finding out the current draw of your device and choose the cable that way, search for current capacity tables for multicore cable, and choose the size which safely carries the amps. You may find 1.5 flex does it?
    • CommentAuthorowlman
    • CommentTimeDec 21st 2019
     
    2.5mm 7 Core CY cable is approx 11.9mm dia. It can vary manufacturer to manufacturer so worth checking. All black numbered cores. 1.5mm same stuff is 9.9mm dia..
    • CommentAuthorgyrogear
    • CommentTimeDec 21st 2019 edited
     
    FWIW, my IIP sibling (ex-senior chief photographer at Ministry of Death...) says :

    "I would agree with djh's advice, and get rid of it, otherwise he could just possibly kill himself. I remember when I was at college, being told that a portable battery-powered electronic flash gun could produce a potential of 1m volts, and heard about somebody who got a hole burned through their finger from one! So imagine what a mains-powered studio flash could do, especially when at least some of it has disintegrated".

    gg

    (edited for unintentional demotion, chief...)
    • CommentAuthorRex
    • CommentTimeDec 21st 2019
     
    As I have not used the unit in some time, getting rid of it is a possibility.

    And I agree with gyrogear, when i worked in a studio, another assistant discharged a studio flash (very powerful) before removing the flash head. He managed to touch the flash tube wires and got a very big bang, that not only shorted out the flash pack, but sent him flying ten feet across the floor. Had a small crater in his thumb but probably lucky to be alive.
    • CommentAuthorRex
    • CommentTimeDec 21st 2019
     
    Apart from the obvious, check the label, is there a way to determine the amps?
    • CommentAuthorphiledge
    • CommentTimeDec 21st 2019
     
    If two of the cores in the existing cable are double insulated its likely the cable is a special and you may struggle to find a replacement.

    Before you think about using any alternative you need to understand why 2 cores are double insulated. I suspect it may be due to a high voltage when the flash goes off so you need to know what the voltage is likely to be and use a suitably voltage rated cable. Typical industrial multicore YY cable is max 600 volt rated insulation between cores with 1000 volt being available over a more limited range
    • CommentAuthorRex
    • CommentTimeDec 21st 2019
     
    Philedge. Very useful information. Now I think I am looking for YY control cable. Have found some 7 core; the version that has 11mm od is 2.5mm2. Wold assume that would be adequate but will do more research before committing to a re-build.

    What exactly does 2.5mm2 mean? Is it the cross section of the copper for any core?
    • CommentAuthorphiledge
    • CommentTimeDec 21st 2019
     
    <blockquote><cite>Posted By: Rex<

    What exactly does 2.5mm2 mean? Is it the cross section of the copper for any core?</blockquote>

    Its the cross sectional area(CSA) of each core- the area that can conduct electricity. For single solid cores its the CSA of the single core. For multi stranded cores its the sum of the CSA's of all the strands so you need to measure a strand, work out the strands area then multiply by the number of strands to get the total CSA

    Dont forget to check the voltage rating which may be a more important aspect than than the CSA/current rating!!
    • CommentAuthorRex
    • CommentTimeDec 21st 2019
     
    So if I measure the diameter of any single core (about 2.5mm) presumably, new cable (probably 7 core) with each core being 2.5mm, that could be OK?

    On the other hand, the internet has thrown up something that may be a bit of luck and will have to be investigated, probably after Christmas. The flash unit was originally made by a company based in Dorking (Surrey) not a million miles from where I live. The company is no longer in existence, but I have found a camera / flash unit repair guy with an address, just outside Dorking. Not holding my breath.

    Will post an update when I know more.
    • CommentAuthorgyrogear
    • CommentTimeDec 21st 2019 edited
     
    Posted By: RexThe company is no longer in existence


    Rex, make sure you *ARE* !
    and bin it LOL

    (my still-around bro says "Rex has got a death wish" )

    gg
    • CommentAuthorMike1
    • CommentTimeDec 21st 2019
     
    Beware using twin and earth; although the conductors are of the headline cross sectional area, the earth is smaller. For example 2.5mm² T&E has 2.5mm² conductors, but only a 1.5mm² earth.

    In fact, beware of using anything other than a pre-manufactured cable.

    Personally I'd go and buy a couple of flash guns or hire in some studio lights...
    • CommentAuthorCWatters
    • CommentTimeDec 23rd 2019
     
    2.5mm diameter is over 4mm^2 in area which I doubt. Think you need to compare the cores with a cable of known cross sectional area.
    • CommentAuthorphiledge
    • CommentTimeDec 23rd 2019 edited
     
    For a single SOLID conductor 2.5mm diameter is just under 5mm2 CSA, but Rex says its multistranded flexible cable so total CSA needs to be worked out as above and will probably need a micrometer or wire guage.

    Probably easiest/safest to use new kit or get the cable replaced professionally.
    • CommentAuthorRex
    • CommentTimeDec 23rd 2019
     
    I have found that trailer manufacturers usually have the sort of cable I believe I need. But it becomes confusing (which is another way of saying, I don't understand.)

    I spoke with the camera / flash repair guy this morning, and in fact, he used to work for the company that made my unit. Of course, he does not have any cable and recommended a trailer company.

    To recap, the existing cable is rubber coated, 11mm o/d, six core and when any core is twisted, it has a core diameter of 1mm. The plug fortunately says 240V / 6A. The individual strands are very fine silver wire, too many to count and too fine to measure without a micrometer.

    The cable that the trailer company have has an o/d of 9mm, 7 cores and when a core is twisted, has a diameter of 1mm. The core is 9 strands of 0.2mm copper wire and the whole cable has a 6A rating.

    According to the repair guy, only two of the cores (black and white) take the high amps to the flash tube; the remaining four cores are for the modelling light and switching, etc. Also, this unit dates from around 1980 and wire technology has moved on quite a lot.

    I also opened the unit to check the state of any internal wiring and it is all PVC insulated, everything nice and flexible so I figure all is OK.

    Am I correct in assuming that a 7 core cable rated at 6A with an individual core of the same diameter as the original (even with the insulation o/d not being the same) is likely to be OK?

    As an aside, the power when the flash fires is instantaneous (obviously) and not therefore continuous. Although the rating is important, the power to the flash is completed in a nano-second; it is only the modelling light that is continuous.
    • CommentAuthorphiledge
    • CommentTimeDec 23rd 2019
     
    Trailer lighting cable is intended for 12/24 volt circuits and as ELV cable doesnt have to be manufactured or tested to any standards. Cable rated for 240 volt should be manufactured and tested to specifc BS EN standards.

    If your intent on going down the DIY repair route be sure your using the right cable. An industrial YY cable is very likely to be rated for 400/600 volts, but as mentioned before, you need to check that voltage rating is adequate.
    • CommentAuthorRex
    • CommentTimeDec 23rd 2019
     
    Thanks for the replies and concern. I certainly don't intend to get a Darwin Award by bodging the fix, but I also don't want to discard the unit just because a length of cable has perished.

    I had not thought about trailer cable being used for 24v!!!

    But what is the difference between trailer cable where the wire cores are 1.2mm o/d when twisted and mains cable where the twisted core is also 1.2mm o/d?

    Also have a sample of a more substantial trailer cable, correct outside diameter, 7 core with the twisted core being 1.5mm diameter

    I also found this https://www.tlc-direct.co.uk/Products/CA0dot75F7.html which is mains control cable with a 6A rating, and that is what is stamped on the plug. Main downside is not colour-coded.
    • CommentAuthorCWatters
    • CommentTimeDec 23rd 2019
     
    Posted By: RexTo recap, the existing cable is rubber coated, 11mm o/d, six core and when any core is twisted, it has a core diameter of 1mm.


    1mm diameter is around 0.8 mm^2. Nearest standards would be either 0.75 mm^2 or 1 mm^2.

    0.75mm^ mains flex is rated for 6A so pretty sure that's what you have. If in doubt 1mm^2 would be safer (10A).
    •  
      CommentAuthordjh
    • CommentTimeDec 23rd 2019
     
    Posted By: RexI certainly don't intend to get a Darwin Award by bodging the fix, but I also don't want to discard the unit just because a length of cable has perished.

    The difficulty we have is that you're repeatedly demonstrating the depth of your ignorance in this area and thus your eminent qualifications to receive a Darwin Award. :devil: Sorry to be blunt.
    • CommentAuthorCWatters
    • CommentTimeDec 23rd 2019
     
    PS If be surprised if 6/7 core 2.5mm^2 was 11mm OD.
    • CommentAuthorCWatters
    • CommentTimeDec 23rd 2019 edited
     
    Nearest I can find is this..

    0.75mm^2
    6 Core
    Silicon Rubber
    OD - contact vendor

    https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F274008272602

    But its expensive and ships from China.

    PVC covered might be easier to find.
    • CommentAuthorRex
    • CommentTimeDec 23rd 2019
     
    "The difficulty we have is that you're repeatedly demonstrating the depth of your ignorance in this area and thus your eminent qualifications to receive a Darwin Award."

    My depth of ignorance is to do with selecting the correct cable. Actually doing the work is something I am more than capable of achieving.
    • CommentAuthorphiledge
    • CommentTimeDec 23rd 2019
     
    @Rex
    Re twisting and measuring multi stranded cable- the harder you twist the thicker the cable becomes so not really a way to measure a cables size
    Re 24v trailer cable- lots of commercial vehicles run at 24volts and if they tow a trailer, its cable will run at 24volts
    Re trailer cable voltage rating- as I tried to point out there are no mandatory standards governing the manufacture of trailer cable. As you dont know the voltage spike your going to put down the cable when the flash goes off you're potentially going to put 100's or 1000's of volts down a cable that may or may not be manufactured to a standard that gives adequate insulation to protect against electric shock. This is a concern about the insulation/voltage rating of the cable which is a completely separate consideration to the core or sheath size.

    Youve said that some of the cores are double insulated which sets alarm bells ringing for me. You need to understand why they are double insulated. If you dont know, then youre probably best getting professional help in choosing a suitable cable
    • CommentAuthorRex
    • CommentTimeDec 24th 2019
     
    Phil,

    Thanks for the explanation. Don't recall where I mentioned double insulation within the cable. The original is all just regular six core.

    CWatters: I contacted the China guys and their reply said the cable was rated for 450 - 750 V but they did not give an amp rating. Also said "inner diameter of individual core =1.8mm" but I did not ask for the specific mm2 section. As it is also tinned copper strands, is probably like the original and very flexible, unlike 9 stranded plain copper.

    There is some double insulation within the flash head, but that is only additional sheathing with the core feed through; no big deal.
    • CommentAuthorphiledge
    • CommentTimeDec 24th 2019
     
    Posted By: Rex<

    Thanks for the explanation. Don't recall where I mentioned double insulation within the cable.


    Third or fourth post you said "sheathed with extra insulation". In your post above you refer to double insulation that the additional sheathing provides, so Im going to forgive myself for getting my wires crossed. An extra sleeve of insulation over a core is called a sleeve and a sheath is normally the outer part of the cable, in my world anyway.

    As you close with "no big deal", I'll trust you have things in hand and leave it at that.
    • CommentAuthorRex
    • CommentTimeDec 24th 2019
     
    My apologies; the extra 'insulation' is indeed just a protective sleeve and my comment of 'no big deal' means that I have some various sleeving so when I decide on the cable, not a big deal to add the sleeving.

    In my continuing search, I have found this (https://gavshop.co.uk/8-pin-bulgin-plug-retro-disco-light-250v-6a-ac-line-fitting-444-p.asp) which is the plug at the end of the cable. But that company do not appear to have six core cable on their site.
   
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