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Thread: Cooktop

  1. #1

    Default Cooktop

    Hello,

    I am replacing a cooktop that is wired with AWG 10 3 insulated wires. My question is what size wire and breaker do I use on the new one. The sticker on it says 7.0kw 120/240v and to the right says 5.3kw 120/208v. Should the wire be copper or aluminum? On the new unit there are 4 wires, red, black, white and green.

    Thanks,

    David

  2. #2
    Plumbing Designer FloridaOrange's Avatar
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    Most instructions will give you the wire size required along with a disclaimer that the given wire size is in copper. They will also give wiring diagrams for 3 wire to 4 wire.

    What's the model and brand?
    Matt
    Semi-professional plumbing designer
    Enjoying life in SW Florida

  3. #3
    In the Trades mattbee24's Avatar
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    If it is rated at 7 kw, it is just over 29 amps at 240v. If it were me, I would run 8/3 with ground romex and put it on a 40a breaker.

  4. #4

    Default Model

    It is a Jenn-Air JED8430BDB, serial number 16252549NR.

  5. #5
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by condor View Post
    \ The sticker on it says 7.0kw 120/240v and to the right says 5.3kw 120/208v.
    240/7 kw = ~8.2 Ω
    208/5.3 kw = ~8.2 Ω
    I guess it makes sense.

    What is the distance back to the panel?
    Last edited by Thatguy; 07-08-2009 at 01:56 PM.

  6. #6

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    Its about 37 feet to the panel.

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    Quote Originally Posted by condor View Post
    Its about 37 feet to the panel.
    OK so if you want a max 5% drop at 240v at 29A you want no more than 12v/29A = 0.4 Ω for 74' loop distance = 5.4 Ω/1000' so you need larger than #16 AWG, copper, for voltage drop.

    For ampacity, it looks like #10 AWG copper would just do it at 29A at 60C insulation. With 90C insulation you could even go to #12.
    http://www.jhlarson.com/ind_tables/c...able310-16.htm

    So it's #10 or #12, copper. For aluminum you need #10 with min. 75C insulation.

    Wood slowly chars at 120C so you can pick your own factor of safety.
    Last edited by Thatguy; 07-08-2009 at 02:47 PM.

  8. #8
    In the Trades killavolt's Avatar
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    Quote Originally Posted by Thatguy View Post
    OK so if you want a max 5% drop at 240v at 29A you want no more than 12v/29A = 0.4 Ω for 74' loop distance = 5.4 Ω/1000' so you need larger than #16 AWG, copper, for voltage drop.

    For ampacity, it looks like #10 AWG copper would just do it at 29A at 60C insulation. With 90C insulation you could even go to #12.
    http://www.jhlarson.com/ind_tables/c...able310-16.htm

    So it's #10 or #12, copper. For aluminum you need #10 with min. 75C insulation.

    Wood slowly chars at 120C so you can pick your own factor of safety.
    Wow, that's hard. Let a guy pick his poison.....

  9. #9
    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by Thatguy View Post
    OK so if you want a max 5% drop at 240v at 29A you want no more than 12v/29A = 0.4 Ω for 74' loop distance = 5.4 Ω/1000' so you need larger than #16 AWG, copper, for voltage drop.

    For ampacity, it looks like #10 AWG copper would just do it at 29A at 60C insulation. With 90C insulation you could even go to #12.
    http://www.jhlarson.com/ind_tables/c...able310-16.htm

    So it's #10 or #12, copper. For aluminum you need #10 with min. 75C insulation.

    Wood slowly chars at 120C so you can pick your own factor of safety.
    I really don't know what to say about some of this.
    The fact that you are doing a VD calculation for a 37' run, or the fact that you are suggesting #12 for a 29A circuit, or that you are suggesting using the 90 deg C column for ampacity.


    Matt is right. This new unit requires a new run of 8/3 w/g and a 40A breaker.
    Answers based on the 2008 & 2011 NEC. If you're on the '14 already I feel sorry for you.

  10. #10
    Homeowner Thatguy's Avatar
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    I should have sized the breaker first?
    Back to the books (that I already have)
    Last edited by Thatguy; 07-08-2009 at 06:41 PM.

  11. #11
    Licensed Electrical Contractor Speedy Petey's Avatar
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    Well, I'll just say that 310.16 is fine, but there are many other sections that alter how we use it.
    For instance, pretty much the only thing we can use the 90 deg column for is derating.
    You also have to be aware of 240.4(D), what it applies to, and what exceptions there are to it.

    The code is not something you get from a chart on a single web page.
    Answers based on the 2008 & 2011 NEC. If you're on the '14 already I feel sorry for you.

  12. #12
    Homeowner Thatguy's Avatar
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    It'll be a while before I live this one down.
    What's the written equivalent of

    Open mouth, insert foot

    ?

  13. #13

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    Thank you all for your answers. I will go with 8/3 and a 40A breaker.

  14. #14

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    One more question, does this romex 8/3 with ground sound ok?

    Conductors:

    * Solid conductors: Soft, uncoated
    * Copper Stranded conductors: Uncoated copper per ASTM-B3 and ASTM-B8

    Conductor Insulation and Jacket:

    * Color coded PVC (polyvinyl chloride), rated 90C dry
    * Insulated conductors also jacketed with clear nylon (polyamide)

    Grounding Conductor:

    * Soft, uncoated copper per ASTM-B3

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