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  1. #1
    Join Date
    Apr 2004
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    Wire size for 40 amp breaker

    I am attempting to hook up two 18000 btu air conditioners to one breaker. There is an existing 240 outlet with 20 amp breakers and I want to branch off to install another outlet. I realize that I have to install a larger breaker to do this. What size wire must be used to support this installation? The a/c's have a 15 amp draw and are 220v.[?]

  2. #2
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    meoli5: If one a/c draws 15a on a 220v/20a line, that's OK. You need another identical (or heavier) protected line for the second a/c.

  3. #3
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    The existing wire for a 20 amp breaker should be 12 gauge. You CAN NOT install a larger breaker on 12 gauge wire, this is a dangerous fire hazzard. A 20 amp breaker and 12 gauge wire is the largest wire that can be installed for a residential receptacle other than a dryer or range.

    You must run a new circuit from your main panel for the new air conditioner as the present 20 amp breaker will not support both units.

  4. #4
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    each ac unit needs it's own breaker.

    But as to your question, 40 amps = # 8 wire.
    Did you ever see OHM'S mother in LAW?...... SHOCKING!

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