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Do I Need a Special Circuit for my Air Conditioner


By Dave Rongey - Summary:

I am replacing an old air conditioner with a more energy efficient model. Do I need a new circuit? Air Conditioner Electrical Circuit Requirements: Replacing an Older Air Conditioner, Converting an Existing Circuit.


Replacing an Air Conditioner

Electrical Question: I am replacing an old air conditioner with a more energy efficient model. Do I need a new circuit?

  • I am replacing an old 18,000 BTU Air Conditioner that ran on a 220volt circuit, the new AC Unit is a more energy efficient model that is 15,000 BTU that runs on 115 volts.
  • I was told a 115volt is what we know as 110volt, but that it is really 110 to 120volt.
  • The 220volt is on it’s own breaker and I want the 115volt to also have it’s own breaker.
  • How do I do this, do I have to trade out the circuit breaker?
  • If I can isolate a 110volt that is close by and make sure nothing else is running on it but the air conditioner can I just use that until I get an electrician who will be upgrading our wiring?
    The lines I’m taking about are 20 to 30 years old and are up to specs, as far as I know.

This electrical wiring question came from: Eileen, from Lawrence, Kansas.

Dave’s Reply:
Thanks for your electrical wiring question Eileen.

Air Conditioner Electrical Requirements

Application: Electrical Circuit Wiring.
Skill Level: Intermediate to Advanced – Best installed by a Licensed Electrical Contractor or Certified Electrician.
Tools Required: Electricians Pouch of Hand Tools for Rough-In Wiring, Electric Drill and Auger Bits and Extension Cord for installing a new circuit.
Estimated Time: Depends on the extent of the project, the type of construction and available access to the project area.
Precaution: Any existing wiring in the immediate area that may interfere with the installation should be identified and turned OFF and Tagged.
Notice: Installing additional electrical wiring for an air conditioner should be done according to local and national electrical codes with a permit and be inspected.

The Basics of Electrical Circuits for Air Conditioners

  1. Should You Share an Outlet or Install a New Electric Circuit?

    • Identify the AC Electrical Requirements:
      • The installation manual or owners manual that comes with the air conditioner should specify if the air conditioner requires it’s own electrical circuit, (keep reading if it does not).
      • Locate the nameplate or specification plate on the ac unit which will have the electrical circuit requirements.
  2. Rule of Thumb for Air Conditioner Circuit Requirements
    • One rule of thumb is if the air conditioner is 110-120 volts and the required amperage is over 7 amps then it would be best to install a dedicated circuit for the air conditioner.
  3. Replacing an Older Air Conditioner
    • If you are replacing an older air conditioner with a new AC and there already is a dedicated circuit then you must make sure that the amperage of the circuit is adequate for the new air conditioner.
    • If the existing circuit is larger and has the same number of required wires as the new ac unit then the outlet receptacle will need to be changed to accommodate the new AC unit cord, and the circuit breaker should be changed to the rated amperage of the new ac unit.
    • IMPORTANT: Never increase the amperage rating of a circuit breaker. The maximum size of a circuit breaker must be sized according to the type of circuit wire or cable that is installed.
  4.  Converting a Dedicated 120 Volt Circuit to Dedicated 240 Volt Circuit

    • If there is a dedicated circuit that is 110-120volt and the new air conditioner requires 220-240 volts then the existing circuit may be converted from 120 to 240 volts if the amperage rating is the same for the existing circuit as the required power for the new ac unit.
    • The neutral wire of the circuit will need to be identified, and remarked as a power conductor with red or black electrical tape.
    • IMPORTANT: The changes in circuit wire designations from 120 volt to 240 volts must also be made at the receptacle outlet.
    • A new 2-pole 240 volt circuit breaker will need to be installed.
    • A new 240 volt receptacle outlet will need to be installed to match the ac cord configuration.
  5.  Converting a Dedicated 240 Volt Circuit to a Dedicated 120 Volt Circuit
    • If there is a dedicated circuit that is 240 volt and the new air conditioner requires 110-120volts then the existing circuit may be converted from 220-240 to 110-120 volts if the amperage rating is the same for the existing circuit as the required power for the new ac unit.
    • One of the circuit wires that is being used for one leg of the 240 volts will need to be identified, and remarked as a neutral wire with white electrical tape.
    • IMPORTANT: The changes in circuit wire designations from 240 volt to 120 volt must also be made at the receptacle outlet.
    • A new single pole 120 volt circuit breaker will need to be installed.
    • A new 120 volt receptacle outlet will need to be installed to match the AC Unit cord configuration.

NOTE: A Dedicated circuit is a circuit that is not shared by any other device.

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