Appropraite Mains Wire

Discussion in 'General Electronics Chat' started by Stuntman, Sep 4, 2012.

  1. Stuntman

    Thread Starter Active Member

    Mar 28, 2011
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    In one of my projects, I have included circuitry to fuse and switch (emergency shutoff) AC mains.

    Power to the module seems straightforward with IEC connectors and power cable.

    However, what is the industry standard for wiring inside the enclosure?

    My first though was simply get some SVT cable, and remove the individual conductors and using crimp connectors and solder joints (where appropriate), route the different leads where they need to go. (IE, the live to the fuse tower, to the switch, then back to the PCB ). The only thing I see wrong with that, is the individual strand insulation seems fairly soft and fragile.

    Is there a type of wire best suited for solder and crimp connections inside and enclosure?
     
  2. Jaguarjoe

    Active Member

    Apr 7, 2010
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    The best type of wire for this is a live wire, or licensed electrician.

    There are so many variables here it would be impossible to guide you without seeing this. The liability is great also.
    AC
    DC
    volts
    amps
    wet or dry
    distance
    code requirements
    and on and on
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    The OP is talking inside his project, not house wiring. You are over complicating the issue.

    If it is inside an enclosure that is out of the weather there are two big issues, voltage and current. If it is low voltage then you have a wider range of wires you can use.

    The big variable is the current. You need wire that can handle the current.

    Typically stranded wire is used for crimp on connectors. I use 18 gauge wire for light weight use all the time. Solid wires typically do not crimp well.

    I can visualize the city wanting to see inside a project I make, not likely. Common sense if making home brewed projects goes a long way.
     
  4. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    In Australia in the hobby electronics catalogues the wire is usually specced for "mains rated" or not. Generally all the thin wire is NOT mains rated, mainly because the insulation is also thin and not suitable for the high mains voltages. Anything like a communications type wire like from coax cable, 'phone wire, or CAT5 cable or anything like that is NOT safe to use.

    As a good example of "mains rated" wire, you can pull apart an old power lead from an appliance, or an old extension lead and take out the individual wires.These will be mains rated and will give you an idea of the cable size and insulation thickness that is appropriate.

    And one of the most important things with mains wiring inside a project is the FUSE. Always buy a proper full-size fuse holder and fuse the mains active or "live" wire where it first enters the enclosure, even before the power switch. I prefer panel mount type fuse holders so you can pull out or inspect the fuse without having to pull apart the whole appliance!
     
  5. BSomer

    Member

    Dec 28, 2011
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    I wasn't too sure what exactly "SVT cable" was, so I did a quick search. According to a couple of manufacturers information, the cable as a whole is rated for 300V. So the individual wires in the cable must be rated at the same voltage. If your project does not exceed this voltage level you should be fine.

    The only thing that would hinder the usage of the wires is amperage. The only sizes of SVT cable I was able to find is 18 AWG and 16 AWG. Again according to the mfg specs, this cable as an assembly is good for up to 10 amps.

    So you should be fine using this wire in your project if you do not exceed 10A @ 300V, you use a proper sized fuse, and ensure all connections are properly crimped or soldered.

    When I was doing electrical installations I often used TFFN stranded wire for my control circuits, usually about 18 AWG. The amperage on these circuits generally were less than 5A. TFFN refers to the type of insulation, which is rated for up to 600V. If you do not already have the wire for your project, I would find some of this wire.

    Hopefully this helps you a little. :)
     
  6. Jaguarjoe

    Active Member

    Apr 7, 2010
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  7. Wendy

    Moderator

    Mar 24, 2008
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    Opps, misread the original post. Tired computing strikes again.

    Hang in there guy, it is a rough road.
     
  8. Stuntman

    Thread Starter Active Member

    Mar 28, 2011
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    All,

    First, thanks for the seemingly obligatory licensed electrician remark.

    I think I asked my question indirectly,

    Is there a type of wire specifically designed for enclosed 120/240V connections? All kinds of electronics have to do this to some degree, TV's, VCR's, Blenders, etc. Just like you use Romex for walls and THHN for conduit, is there a correct wire type for his application.

    Again, splitting apart the SVT was simple enough, but i really felt like the individual conductor insulation (not the black outside jacket) was very soft and fragile. The last thing I'd want is it marring against something then shorting out somewhere.

    BSOMER - So is TFFN approved for soldering and crimping like one would do in an enclosure? This is very interesting, seems about right:

    http://www.southwire.com/products/oem-tffn-tfn-tewn.htm
     
  9. BSomer

    Member

    Dec 28, 2011
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    I don't know if there is a specific type of wire for enclosed connections. The way I understand it is that you figure out what voltage/amperage you will be working with and the environment the wire will be in. Different types of insulation handle heat better than others. Some are more flexible, some more resistant to chemicals. It really comes down to what your requirements are. As long as the wire you use meets, at a minimum, your voltage and amperage requirements it will work.

    And yes, TFFN is good for soldering and crimp terminals.
     
  10. gerty

    AAC Fanatic!

    Aug 30, 2007
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    Last edited: Sep 6, 2012
  11. Jaguarjoe

    Active Member

    Apr 7, 2010
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    Before solid state solidified, everything was at some high potential ('cept for battery stuff which rarely exceeded 90v). I recall hook up wire was good for 600v.

    Be cautious if you buy off brand wire- some of it is copper coated steel which sells for about 50% of the good stuff price.
     
  12. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Maybe we are a bit more sensitive in a 240v mains country, but to me cable is either "mains rated" or it is not. Communications cable and compound cable (like multicore alarm cable etc) is not suitable.

    I googled "SVT cable" and found a lot of 3 core cables that look like mains cables, some even have mains plugs.

    BUT If you are even a bit unsure that your cable is "mains rated" then I suggest you play it safe and get some cable out of a mains power lead as I suggested before. Also fusing, wire connection quality, grommets to protect from cable pull etc are all very important for safety!
     
  13. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    A lot of it would depend on compliance. If you are wanting to emulate a UL rating, you'll need thier specs. I suspect the NEC (I'm CEC) refers to 'machine wiring' and it's requirements.

    Because wiring 'within' an enclosure is not subject to personal exposure, it has a broader allowance. The 'enclosure' often becomes the point of interest, with certain demands placed upon it. For sure though, consideration needs to be placed on ensuring that a conductor remains intact throughout it's intended use. This often means that conductors must be mechanically connected, with solder only be used for electrical integrity. Insulation, within the enclosure can often be air, but only if the conductors are rigid in thier seperation, which often means mechanical support.

    In general, make sure that whatever supports your circuitry, is rigid. Make sure that penetrations through the enclosure do not errode conductors (bushings), and that conductors are strain relieved.
     
  14. Stuntman

    Thread Starter Active Member

    Mar 28, 2011
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    Interesting information. Sounds like for now, I will stick with my service cord "pull-aparts". Perhaps I will find some that has a little tougher individual conductor insulation.

    THE_RB - Yes, SVT is mains voltage service cable. If it has a J (such as SJT), it is for lighter duty (300V) and if it does not have J, it is 600V rated.

    The V in the SVT stands for vacuum. This cord was originally designed to run in vacuum cleaners as it featured a smaller OD and is very flexible (for obvious reasons). This type of service cord has since made it's way into power tool cords, and computer power supply cords (which is where I got mine).
     
  15. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Ahh vacuum cleaner power cable is often a bit softer in the insulation material, for better felxibility. Part of its safety comes from the outer sheath that holds the 3 wires in position and protects them from damage.

    I guess it would be safe in an enclosure if the softness is ok (no chance of crush damage) and it might not be rated for a lot of heat so be careful if a wire touches a heatsink or hot resistors etc. Gnerally it's good to keep the mains wires away from everything in the enclosure and well secured; clamped, glued or siliconed down.

    Anyway you sound like you know what you are doing. :)
     
  16. Stuntman

    Thread Starter Active Member

    Mar 28, 2011
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    Solution: So I have to admit, I finally decided to take a look at my general purpose "hook-up" wire to see what voltage it is rated at. Low and behold, it is 300V rated.

    In digging a little deeper, I found that most "hook-up" wire, is called AWM (Appliance Wiring Material). Seemed interesting that the TFFN that BSomer suggested seemed very similar. Going further, I realized that AWM is seemingly TFFN with a higher (105C) temp rating. (http://www.southwire.com/products/TFFNTFNTEWNOEM.htm)

    Bottom line, your general purpose hook-up wire is probably well suited for 120V applications.
     
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