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How to pick the right insulating type

  1. Jul 12, 2013 #1
    Hi guys. I am an electrical student, and i was wondering if you can help me understand how to pick the proper insulation or what / where / when to use the diffirent type of insulation.

    as of the moment i made a ideal senario, i will use a 8 AWG at 90 C and 75 C, both will be use in ceiling and embeded installation, so what kind of insulation should i use (XPLE, SWA, PVC, MCC ..., ect) thanks in advance.
     
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  3. Jul 13, 2013 #2

    Simon Bridge

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    Welcome to PF;
    Do you mean thermal insulation or electrical insulation?
    I'm kinda veering towards thermal but would like to be sure...
     
  4. Jul 13, 2013 #3

    Baluncore

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    Last edited by a moderator: May 6, 2017
  5. Jul 13, 2013 #4
    @ Simon

    as of the moment thermal insulation is what i am studying for
     
  6. Jul 13, 2013 #5

    Simon Bridge

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    Cool.
    Construction standards and regulations are the minimum level ... it will provide the selection to work from.
    After that you have to decide on what other constraints you will have.
    i.e. you may want maximum insulation (choose whatever slows the rate of heat the most) or you may prefer to maximize friendliness to the envorinment (define what this means to you) or just look for the most economic for your use.

    What you are insulating will be important - lagging a pipe is different from insulating a loft.

    If the decision is for a job you are doing for someone else, where it's your behind on the line if you make a bad choice, then you need to work out a table of the different properties that are important and a weighting factor for how important each property is to the job along the top row and the vertical (LHS) will be a list of the commercial products available - fill in the table with how well each product serves each property and use a weighted sum on each row. Highest score wins.
     
  7. Jul 13, 2013 #6

    sophiecentaur

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    The only safe answer is to be found by reading the manufacturer's specification for their various types of cable. The essential thing to know is the current that your cable will be carrying. The specs you will find are all pretty conservative so you can rely on them - as long as you are 'honest' about your requirements.
    In practice, I think you'll find that PVC is the most common insulation in domestic and office premises. Mostly, the operating temperature of cables is set by the power they are carrying and the presence of other thermal insulation, rather than external heat sources. Where there are other heat sources (in heating equipment or for fire alarm circuits), you need specialist advice.
     
  8. Jul 13, 2013 #7

    Simon Bridge

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    Oh yes ... choosing electrical insulation but concerned about heat is another interpretation :/
    So checked some of the acronyms ...

    XLPE (XPLE does not seem to register) = cross linked polyethylene can be an electrical insulation, but it is also available in big sheets for thermally insulating pipes and ducts. This was what prompted me to ask the question.

    SWA = Steel Wire Armored - a type of cable ... armoring rather than insulation though.

    PVC = Polyvinyl Chloride ... almost all electrical ... so now I'm veering...

    MCC - I only have hits for motorcycle engines.

    Someone will have a useful answer I guess :)
     
  9. Jul 13, 2013 #8

    jim hardy

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    If this is for wire going into a building, the National Electrical Code is the document to follow.

    Here's an introductory article
    http://www.nmsu.edu/~tdi/pdf-resources/cc66.pdf [Broken]

    a search on " NEC insulation " returns a smorgasboard of references ranging from the sublime to the ridiculous.

    This one looked useful
    http://www.ul.com/global/documents/...ctrical/newsletters/W&CMG_April2007_Final.pdf

    next - go to your local lumberyard and see what is on their racks. You should find THHN which will probably do for most building. Stranded is easier to pull but can be harder to terminate.
    If it's inside an appliance like a stove or fireplace you need glass insulated appliance wire. That stuff used to be common, but on a recent visit to a friend's house we had to look all over Denver for some to fix his gas fireplace fan controller. Finally found a roll left over from 1960's in a really old hardware store but I cannot remember its letter designation. When you see an old electric stove discarded it's worth salvaging a few feet from it for such "emergencies". The wire to the heating elements is high temperature.

    My nuclear plant was wired largely with tray cable having a 20 mil layer of clear XLPE, color coded PVC insulation around that, and black PVC jacket overall. XLPE has good radiation resistance and it is still pliable after forty years of service.

    old jim
     
    Last edited by a moderator: May 6, 2017
  10. Jul 13, 2013 #9

    sophiecentaur

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    HAHA

    Waste not, want not, eh, Jim? But stuff that old is almost certainly not going to meet the present regs, is it? (even the colours are wrong for UK installations) Anything permanent has really got to obey the regs or, when you want to sell up or make any insurance claim, (not necessarily related in any way) you could find that an uncertificated bit of wiring could end up costing you.
    Just follow the regs (which are always on the safe side. You should be able to rest easy at nights, too.
    @chinrose: I should hope that, in your Engineering course, they will give you at least something about Specs, Regs, Safety and Liability before they give you your 007 rating! lol
     
  11. Jul 13, 2013 #10

    jim hardy

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    Waste no want not - Indeed.
    And always "overbuild - if you need 200 deg wire use 400.

    I found a whole spool of military 1000 volt 1000 degF glass braid insulated wire at my salvage yard for next high temp repair. One needs to keep an eye peeled for such treasures. There's a mil-spec manufacturer in town so all sorts of neat stuff shows up at the metal recycler.

    You won't find this stuff at your local home supply store

    http://www.daburn.com/2498hightemperatureleadwire1500ftemperaturerating.aspx

    http://wire.thermalwire.com/viewitems/cable-600v-single-conductor-538-176-c-to-125-176-c/8-176-c-600v-heavy-duty-high-temperature-lead-wire? [Broken]

    http://www.brimelectronics.com/glasswire.htm

    One needs to be aware that such specialty wires exist and for good reason.
    Using ordinary hardware store wire to replace above types is inviting pyrotechnics. Not to mention the legal troubles Sophie mentioned........

    Fortunately we have standards and codes. They are the result of hard lessons.
    Here in US we have a marvelously detailed National Electrical Code that'll keep you out of trouble.

    As Sophie says - follow the standards. If in doubt look it up.


    old jim
     
    Last edited by a moderator: May 6, 2017
  12. Jul 13, 2013 #11
    Metal Clad Cable
     
  13. Jul 14, 2013 #12
    To: ALL

    Thanks for the reply, you all help me to check all the most needed points to consider my design, cheers.
     
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