How to install a new 220VAC electrical circuit to an air conditioning condensing unit.
When it comes to air conditioning installations, there is usually very little that the homeowner can do. However if you are relatively handy you can install the electrical service to the outdoor condenser unit and then leave the refrigeration work to the professionals.
Remember that you should always check with your local building department to determine what type of permit is required for the total installation of an air conditioning system. Homeowners are usually allowed to perform electrical and plumbing work without a license. By having the work permitted and inspected you will not only increase the chances for a successful installation, you will not void your homeowner’s insurance policy and you will not have any issues when you go to sell your home in the future.
The Electrical Circuit
The electrical circuit needed to power your outdoor air conditioner condenser is typically a double pole circuit breaker in your home load center (panelboard) that goes to an air conditioner service disconnect switch and from the disconnect switch to the condenser.
A 220 VAC circuit requires two (2) vacant circuit breaker positions located together in the panelboard. From the circuit breaker you will run the appropriate size cable to the outdoor air conditioning disconnect switch. From the disconnect switch you run the wires to the air conditioner. The size of the wire depends on a few important factors; the circuit size which is determined by the unit, the length of the run from the unit to the panelboard, and the insulation on the wire. Also check the installation instructions on the condenser unit. Some models may require both 120VAC and 240 VAC; in this case you would need to run 3-conductor wire, red, black, white and a ground.
You may need to make sure that your electrical service has the capacity for new air conditioning equipment if you are adding it to an existing home. Contact your utility for more information.
Wire Size Calculator: http://www.elec-toolbox.com/calculators/voltdrop.htm
Note: The longer the circuit length the greater the voltage drop. Usually circuits over 40 feet in length need the wire size increased to the next largest wire size. For a 30A circuit you may need #10 wire and for a 45A circuit your may need #8 wire.
Tools and Materials
Voltage Meter or Tester
Drill and Drill Bits
Flat and Philips Screwdrivers
Galvanized screws, for mounting disconnect
Wire, #12, #10, or #8 and a ground wire
Flexible Liquid-tight conduit
Double-Pole Circuit Breaker
1. Mount the air conditioner disconnect on the exterior of the home as close to the air conditioner condenser as is reasonable. Ensure that it is securely fastened to the wall using proper fastening hardware for the wall material. The National Electrical Code is typically followed but may be interpreted differently by the building inspector. Usually it needs to be readily accessible and within line of sight which can mean within arm’s reach or within 6 feet. Check with you local code official for clarification.
2. The air conditioner disconnect is connected to the air conditioner condenser with liquid-tight flexible metallic conduit, sometimes referred to as “seal-tight.” The size of the conduit is dependent upon the wire size, for #10 use 1/2” conduit and for #8 use 3/4” conduit. (This is for 2 wire conductors.) Liquid-tight conduit can be purchased at electrical distributors and most home centers.
The conduit is mechanically connected to the disconnect and the condenser using the appropriate straight or 90° flexible metallic conduit fittings. These fittings transition from the PVC coated conduit to a metal fitting
90-Degree Liquid-tight fitting
Add conduit clamps within 12 inches from the disconnect and another at the last point on the wall prior to the conduit heading towards the condenser.
3. Run the appropriately sized wires through the liquid-tight conduit. While you can purchase and run sheathed cable, it is better to purchase individual conductors of the correct wire gauge and length. They can be purchased at electrical distributors and home centers. The length of the wire should be about 24 inches longer than the conduit itself.
Since both wires are conductors in 240VAC circuits, buy wires with black insulation to identify them properly. If you use sheathed cable that has one black and one white wire, you need to wrap the ends on the white wire with black electrical tape.
4. Connect the wires in the air conditioning condenser junction box.
The bare copper wire is the ground wire which needs to be connected to the green wire in the condenser junction box. This may be a lug or screw connection depending on the manufacturer. In either case the ground wire is connected to the metal frame of the air conditioner condenser.
Inside of a Condensing Unit: The liquid-tight conduit is coming in at the bottom (1), the two black conductors are connected to the relay on the left (2), and the ground wire is connected to a lug on the left side of the frame (3).
The other 2 wires supply the 220 VAC to the condenser. The location and method of connection for these two wires will be described in the installation manual that came with the condenser.
5. Connect the wires to the inside terminals or lugs in the disconnect. The bare copper wire will attach to a lug or screw that is connected to the frame of the disconnect. The other two wires will connect to lugs or screws that are identified as “LOAD”. It does not matter which load wire goes to which lug or screw. Check with your local code official to determine if they require a fused disconnect, which is not typical, or a non-fused pullout disconnect.
Pullout Service Disconnect
6. Run the wires from the service disconnect to the electrical load center. If the cable is going through an unfinished basement or in a crawl space under a home you can use sheathed cable. However, anywhere where the cable is in a location where it can be damaged it must be protected. For this reason it is better to run the wires inside rigid PVC conduit or the flexible conduit to an electrical junction box and from that point on to the load center.
Use conduit clamps to fasten the conduit to the wall or joists. In areas where sheathed cable is running through a basement the cable must secured using clamps or staples every 36 inches and within 12 inches of any electrical box or the load center panel.
7. Turn the power "OFF" at the load center. This is accomplished by either turning "OFF" the main breaker or at a disconnect switch located between the utilities electrical meter and the load center. You will most likely need to remove a “knockout” from the load center either at the top of bottom. Use a fitting to protect the wires going through the knockout hole.
IMPORTANT: Turning the main breaker to the "OFF" position does not remove all power from the load center. Power has been turned "OFF" to the individual circuit breakers, but there is still live power on the incoming lugs of the main breaker.
Remove the inner load center panel that covers the electrical connections to the circuit breakers.
IMPORTANT: When you have turned the power to the "OFF" position, ensure that there is no power at the breakers by using a volt meter.
8. You must install a double pole breaker in the load center panel. The size of the breaker depends on the electrical requirements of your air conditioner condenser. It can be 30, 45, or 60 Amp.
Double-Pole Breakers shown with red and black wires.
A double pole circuit breaker takes up two vertical positions in the load center. If you have two horizontal positions available you can move one of the current circuit breakers in order to free up two vertical breaker positions.
Note: Do not install two wires on one circuit breaker in order to free up space.
Note: You must purchase a double pole circuit breaker that is designed for your load center. There is no standard mounting configuration for circuit breakers in load centers. The front of the breaker will have the name of the manufacturer and type which is usually 3 or 4 letters.
Once you have installed the new double pole circuit breakers connect the load wires, one to each of the circuit breaker lugs.
9. Connect the ground wire to the ground bar or lug in the load center panel.
10. Replace the circuit breaker cover panel.
Leave the new double pole circuit breaker "OFF" until the installation of the air condition system has been completed by your HVAC technician.
11. Turn the main breaker or the main disconnect switch back to the "ON" position.
After the system has been completed, call your building inspector for a final inspection.
By taking the time to properly install the electrical service to your air conditioning system you can save yourself a few hundred dollars.