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    eric1901's Avatar
    eric1901 Posts: 3, Reputation: 1
    New Member
    		  
    #1

    Dec 6, 2008, 07:01 PM
    How do I determine breaker amps on a 240v double breaker?
    Hi,
    I have a new elec. Cooktop that needs 240V, 40 amps.

    Each pole of the double pole breaker for my cooktop circuit
    Says 30amps. So can this 240v circuit support 60 amps, or just
    30?

    Thanks!
    KISS's Avatar
    KISS Posts: 12,510, Reputation: 839
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    #2

    Dec 6, 2008, 07:10 PM

    The markings on a double pole breaker don't add. Ideally we'd need the approximate length of the wire and the type of wire (Copper or aluminum) to make a determination if you can just change the breaker.

    Some cooktops are requiring a 4-wire circuit.
    stanfortyman's Avatar
    stanfortyman Posts: 5,598, Reputation: 279
    Electrical & Lighting Expert
    		  
    #3

    Dec 6, 2008, 07:10 PM
    You do not add the breaker poles. A 2-pole 30 is 30A @ 240v. Since this is probably wired with #10cu it is not enough for your required 40A circuit.

    Can you confirm what size wire was run?
    tkrussell's Avatar
    tkrussell Posts: 9,659, Reputation: 725
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    #4

    Dec 6, 2008, 07:14 PM
    The cooktop circuit breaker is only 30 amps, there are two poles to deliver 240 volts, 30 amps for each. Do not add the two values.

    The existing cable to the cooktop is probably #10 copper wire.

    The new cooktop will need a new 40 amp 240 volt circuit, complete with a new 2 pole 240 volt 40 amp breaker, and a minimum of #8 copper wire.

    Usually Type NM-B (AKA Romex) cable is used.

    What kind of cable is in your home?

    If the new cooktop is rated only 240 volts, then #8 - 2 wire with ground is needed.

    If the new cooktop is actually rated 120/240 volts, then #8 - 3 wire cable with ground is required.

    See the manufacture's instructions AND the nameplate on the unit for this info.
    eric1901's Avatar
    eric1901 Posts: 3, Reputation: 1
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    #5

    Dec 6, 2008, 10:23 PM

    Thanks for all the quick replies.

    I will be checking the wire size; I need to get a gauge for
    That, the wire is not marked.
    donf's Avatar
    donf Posts: 5,679, Reputation: 582
    Printers & Electronics Expert
    		  
    #6

    Dec 8, 2008, 12:14 PM
    Question, are you discussing a 30 amp cook top or are you describing a range/oven appliance.

    If the instructions for new appliance says you need 40 amps, then you have to change the entire circuit.

    You need to replace the existing breaker with a 40 amp breaker. The existing conductors from the breaker to the appliance wall need to be rated for 40 amps (#8 AWG/3). You also need to either install a new receptacle that is rated for at least 40 amp or higher.

    The appliance cord would also need to rated for 40 amps (#8 AWG/3).

    You cannot use a direct wire to the supply. There must be a disconnect at the range to allow the range to be serviced.
    eric1901's Avatar
    eric1901 Posts: 3, Reputation: 1
    New Member
    		  
    #7

    Dec 8, 2008, 08:23 PM

    Hello, I was able to measure the wire for the cooktop, it is
    10gauge-- so I would need to swap it out for the 8gauge
    According to the helpful advice given.

    At this point, I am going to return the cooktop for now
    And look for a 30amp one(which seems to be rare).

    Thanks again for all the responses
    donf's Avatar
    donf Posts: 5,679, Reputation: 582
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    #8

    Dec 9, 2008, 07:16 AM
    According to NEC section 210.19 (A) (3) for ranges 8.75 kW (8,750 Watts) or more rating, minimum branch circuit rating shall be 40 amps. Example : Watts / Voltage = Amps 8750 / 240 = 37 amps (rounded up).

    By inferance, lower wattage cooking units are less than 40 amps. For example: Watts / Voltage = Amps 7000 / 240 = 30 amps (rounded up).
    ranges:
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