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Installing a 220 Volt Circuit for an Air Conditioner

June 28, 2006

Q: How do I run a 220 line for air condition out side unit? Please give directions from fuse panel to outside panel.

A: The first thing you need to do is check with your local inspector and see if you need a permit before beginning any work.

Next you need to turn off the electrical power to this circuit and verify that the power is off using a volt meter.

Your air condenser unit will have a nameplate on it with the electrical requirements. Most units we install here in Montana require 30 amps @ 230 volts. We have also seen a few larger units that require 40 amps. 10/2 Romex is rated for 30 amps and 8/2 is rated for 45 amps.

I recommend starting outside and working back to your electrical panel.

Outside at the condensing unit you need to install an air conditioner disconnect. You can find these at your local Home Depot or Lowe’s. This box is weatherproof and is rated according to the amperage requirements of your unit. This will mount on the outside wall near the condensing unit.

From the disconnect to the unit, you need to install 1/2″ liquid tite flexible metallic conduit for 30 amps and 3/4″ liquid tite flexible metallic conduit for 40 amps. Most units require 1 straight connector at the disconnect and 1 90 degree connector at the unit. You also need to install 2 – 1/2″ 1 hole straps on the conduit for support; one approximately 1 foot from the connector at the disconnect and one at the closest point along the house wall before the conduit turns to connect to your condensing unit.

In this conduit you need to install 2 hots and 1 ground wire. When using the conductors from your Romex, you need to remove the outer sheath before installing them in the conduit. In the condensing unit’s wiring compartment you will find a green wire attached to the metal frame; terminate this to the bare ground wire coming from your conduit. The two hots will terminate to either 2 wires, a terminal strip or a motor starter. Your unit will come with instructions on where to terminate these wires.

The bare copper wire is your ground and it will terminate to the little ground bar or lug attached to the metal frame of the disconnect. The wires coming out of the conduit at the disconnect will terminate to the “load” side of the disconnect. These terminals are marked as “load” in the disconnect.

Then you need to install your Romex from your disconnect to your electrical panel. Without seeing your place, I can’t tell you how to get from point A to point B. Typically, we run these wires in an unfinished basement or crawl space. Your Romex needs a connector at each end and requires a staple within 12 inches of each connector and every 3 feet thereafter. The Romex needs to be protected where subject to physical damage; like the short distance it pokes outside your rim joist and goes up to the disconnect.

Terminate the bare copper ground wire at the disconnect to your ground bar or lug and the two wires to the line side terminals.

Now you want to turn off power to your electrical panel. This is either done with a main breaker in the panel or outside at your meter box location. If you turn off power outside be sure to verify that your power is off at the panel with a volt meter. If you turn off power at a main breaker in your panel, be careful as the wires entering that main breaker will remain live. This may be a good job for a licensed electrician. Most electrical contractors will do this, allow you to do most of the work and then come and inspect your work and terminate the wires in your electrical panel.

Next you need to terminate your ground wire to the ground bar in your electrical panel. Then install your 2-pole breaker and terminate the two hot wires to it. Put the panel cover back on and turn on the power to the panel. You need to check with your air conditioner person before turning on the power to the unit. Most times they want to start the unit for the first time to check for leaks or problems.

Always remember safety first when working with electricity. Never work with live electricity. Always test to verify that the power is off before touching any wires.

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2 Responses to “Installing a 220 Volt Circuit for an Air Conditioner”

  1. Glenn M on March 31st, 2010 7:18 am

    Regarding the Air Conditioner Disconnect? What do you use around the box to keep moisture from penetrating the rear of the box mounted to the house? Is Silicone Caulk sufficient? Thanks, Glenn

  2. Mildred Nashman on May 23rd, 2011 8:51 am

    What is the maximum distance from the disconnect to the condenser?

    Someone has told me that I must install a receptacle within 6 feet of the disconnect – is that correct?