Cooktop

Discussion in 'Electrical Forum discussion & Blog' started by condor, Jul 8, 2009.

  1. condor

    condor New Member

    Messages:
    5
    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. FloridaOrange

    FloridaOrange Plumbing Designer

    Messages:
    1,317
    Location:
    SW Florida
    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?
  3. mattbee24

    mattbee24 In the Trades

    Messages:
    100
    Location:
    Fremont, OH
    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. condor

    condor New Member

    Messages:
    5
    Model

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

    Thatguy Homeowner

    Messages:
    1,460
    Location:
    MD
    240²/7 kw = ~8.2 Ω
    208²/5.3 kw = ~8.2 Ω
    I guess it makes sense. :D

    What is the distance back to the panel?
    Last edited: Jul 8, 2009
  6. condor

    condor New Member

    Messages:
    5
    Its about 37 feet to the panel.
  7. Thatguy

    Thatguy Homeowner

    Messages:
    1,460
    Location:
    MD
    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 60°C insulation. With 90°C insulation you could even go to #12.
    http://www.jhlarson.com/ind_tables/conductor/table310-16.htm

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

    Wood slowly chars at 120°C so you can pick your own factor of safety. :)
    Last edited: Jul 8, 2009
  8. killavolt

    killavolt In the Trades

    Messages:
    33
    Location:
    Southington CT
    Wow, that's hard. Let a guy pick his poison.....;)
  9. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    991
    Location:
    NY State, USA
    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. :rolleyes:


    Matt is right. This new unit requires a new run of 8/3 w/g and a 40A breaker.
  10. Thatguy

    Thatguy Homeowner

    Messages:
    1,460
    Location:
    MD
    I should have sized the breaker first?
    Back to the books (that I already have) :(
    Last edited: Jul 8, 2009
  11. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    991
    Location:
    NY State, USA
    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.
  12. Thatguy

    Thatguy Homeowner

    Messages:
    1,460
    Location:
    MD
    It'll be a while before I live this one down. :eek:
    What's the written equivalent of

    Open mouth, insert foot

    ?
    :D
  13. condor

    condor New Member

    Messages:
    5
    Thank you all for your answers. I will go with 8/3 and a 40A breaker.
  14. condor

    condor New Member

    Messages:
    5
    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 90°C dry
    * Insulated conductors also jacketed with clear nylon (polyamide)

    Grounding Conductor:

    * Soft, uncoated copper per ASTM-B3
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