How to Wire an AC Disconnect | DoItYourself.com (2023)

Sometimes you just need to shut it down. In electrical work and construction, a disconnect switch, also known as an isolator, can be used to separate an electrical circuit from the main power source. This can help ensure the equipment is completely de-energized while performing maintenance or servicing, eliminating the need to go back to the main electric panel every time it needs to be turned off and on.

Disconnect switches can be especially helpful for large appliances located far from your home's breaker, as is often the case with outdoor AC units. Electrical work like this is typically a job for a professional, and in some cases, it's even illegal to do without certification, but if you're interested in learning about this process, these are the steps.

Considerations Before Starting

Adding a disconnect to an existing AC unit is essentially a matter of cutting the 240 volt feed to the AC unit and adding the disconnect in between, thus bridging the current flow through to the AC unit.

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You can also fit a disconnect switch while installing a new AC unit, which makes it easier to choose a practical location.

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(Video) How to install an A. C. Disconnect

Safety First

When adding a disconnect to an already existing AC, the first thing to do is to go to the main electric panel and turn OFF the 240-Volts circuit breaker indicated in Figure 3. This is a crucial step to avoid serious accidents, like potentially fatal shocks.

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For a new installation, it is the main breaker in Figure 4 instead that will be turned off in Step 4. If you're not sure what switches govern which areas, play it safe and shut the power down completely.

Step 1 - Choose the Switch Location

The disconnect switch should be screwed into place on the wall next to the AC unit. Depending on where the cables will be inserted into the switch box, the proper knock-out plugs can be removed once you've mounted the switch, and cable connectors can be fastened into place.

If the disconnect is added to an existing AC Unit, it should be within reach of the already existing cable, so only a short cable is needed to bridge the switch to the AC unit.

Step 2 - Prepare to Wire the Disconnect Switch

With the breaker turned OFF, the wires can be disconnected and the cable removed from the electrical compartment of the AC Unit.

(Video) How to Install an AC Disconnect

For a new AC installation, a cable must be installed from the disconnect to reach up to the main electric panel. A hole must be drilled through the wall to bring the cable inside. It’s a good practice to pre-drill a smaller hole with a long drill bit to make sure it’s where it should be and avoid unpleasant surprises. The hole can then be drilled to its full size to accommodate the cable. Passing the cable through can be done more easily from the inside when the panel is some distance away.

For either case, this cable, the feed line from the main electric panel, has to be prepared by stripping some of its external jacket to expose the wires. Remove about .75 inches (19 mm) of their insulation before inserting the cable into the cable connector and clamping it in place in the disconnect box. Then, cut another cable of the same rating with about 16-20 extra inches and prepare it at both ends in the same manner.

One end of this cable is then inserted and secured into the AC unit’s electric panel, while the other end is fixed in the same manner into the disconnect switch, where it is secured at both ends with cable connectors. The wires can now be connected to their respective terminals inside the AC’s electrical box by matching their colors with the colors of the wires already in place. With this done, the cover can be put back on the AC’s electric box.

Step 3 - Hook up the Disconnect

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The disconnect switch is shown in Figures 5, 6, and 7. Figure 5 shows a pullout switch with the cover lifted and. Remove the double-contact pullout inside (Figure 6) to open both contacts of the switch.

Figure 7 is the same switch with all covers removed, showing where to connect the wires so both red wires go to one set of contacts, while the black wires go to the other set of contacts, which can both be disconnected by pulling a handle.

(Video) How to Wire a Disconnect Box for an Air Conditioner

The two ground wires go to the ground terminals, and, finally, the two white neutral wires are simply connected together inside with a wire nut.

If this is a standard 240v installation, you may be using two wire cable with ground to supply power to the disconnect. In that case, the white and black wires would go to the contacts and the ground wire to the ground block. The white wire of the cable should be remarked a different color to indicate it's not being used as a neutral wire. Black tape is acceptable.

Remember to put the covers back once you're done.

How to Wire an AC Disconnect | DoItYourself.com (5)

If this was an addition to an existing AC unit, the dedicated breaker can be turned back on—ready to go.

Step 4 - Wire the AC to the Electric Panel

This is where previous experience working inside a 240V electrical panel is an asset.

(Video) Install 30 amp ac disconnect (run conduit and wires)

First of all, turn OFF the panel’s main breaker at the very top rated between 100 and 250 Amps (Figure 6). This will switch off everything electrical in the house, so the work should be carefully planned ahead to minimize the extent of the interruption to appliances like fridges and freezers. With this done, the front cover of the large panel can be removed, exposing a whole bunch of wires and breakers.

Once the spot is picked, a 240 Volts circuit breaker can be installed and secured in place in the OFF position. The most appropriate knockout plug for the wiring can then removed and the cable connector installed.

Measure the length of the wires so you know they'll reach from the breaker’s terminals to the knockout hole, accounting for all the bends and the .75 inch (19 mm) skinning to set them in their terminals.

Mark the cable’s jacket at that length, and cut the outer jacket across its perimeter, separating it from the rest of the cable. Use a utility knife, and take care to apply only light pressure while cutting, to avoid slicing into the insulation. Once this is done, cut the jacket through from that cut right to the end and remove the outer layer, exposing a black, a red, a white, and a ground wire.

Pass the cable through the cable connector until half an inch of the jacket shows inside to protect the wires from the clamp. After the .75 inches (19 mm) of insulation are removed from the end of each wire, the bare copper wire can be wired to the ground bus bar, the white wire to the neutral bus bar, and the black and red-colored wires to each one of the two terminals on the circuit breaker. It doesn't matter which of the two goes where.

Step 5 - Turn the Power Back On

To prevent a surge of power through the house, it's a good idea to switch all the breakers off inside the electric panel before switching on the main power breaker. Then, starting with the main breaker, turn every breaker back ON one at a time, leaving the newly added breaker for last.

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FAQs

How Far Can AC disconnect be from unit? ›

This distance is typically described as within 50 feet (15 meters), and in practice at most residential properties the disconnect is much closer (3-6 ft), on a wall or standard near the compressor/condenser unit.

How high should my AC disconnect box be? ›

The disconnect is permitted to be located adjacent to the equipment. Generally, disconnect switches have a height limit of not greater than 2.0 m (6 ft 7 in.) above the floor or working platform as indicated in 404.8(A).

What size breaker do I need for AC disconnect? ›

Bigger 5+ ton units require up to 65A breakers. Most homeowners usually need help with determining the breaker size for 220/240V breakers. For smaller 1-ton (or up to and including 15,000 BTU) AC units, you only need a standard 110/120V circuit with the standard 15 amp breaker.

Does AC disconnect need neutral? ›

There should be a neutral wire if the unit is Y (or star) connected. If all of the internal parts are only connected line-line (i.e. delta load) there is no need for a neutral as there is no current path through the device to neutral.

What is the six disconnect rule? ›

The rule is six disconnecting means for each service, not six service disconnecting means per building. If the building has two services, you can have a total of 12 service disconnects (six disconnects per service).

Can a breaker be used as a disconnect? ›

A switch or circuit breaker shall be permitted to be used as both the controller and disconnecting means if it complies with 430.111(A) and is one of the types specified in 430.111(B).

What's the minimum height on a disconnect? ›

Note: 550.32(F) requires the outdoor mobile home disconnect to be installed so the bottom of the enclosure is not less than 2 ft above finished grade or working platform.

What is the minimum height of an electrical disconnect? ›

The minimum working space height required for the disconnect switch is 61/2 feet (see Figure 6). The minimum working space height for electrical equipment has not always been 61/2 feet. For many years, the working space height (or headroom) was required to be at least 61/4 feet (or 6 feet, 3 inches).

What is the minimum depth for working clearance for an AC disconnect? ›

The National Electrical Code® (NEC)® Section 110.26 requires adequate working space for all electrical equipment. NEC Section 110.26(A) requires a clear space at least 30 inches wide and 36 inches deep if the equipment is likely to be worked on while energized.

Can 10 gauge wire handle 35 amps? ›

For example, 10 gauge wire can handle up to 35 amps. If you need a smaller wire for your circuit, use a smaller gauge. One of the most common uses for a 35-amp circuit breaker is overload and short-circuit protection. These circuit breakers can protect you and your home from any damage caused by electricity.

Can you use 10 2 wire for an air conditioner? ›

Well, a 10/2 already has a 70A ampacity and can allow for a 56 amp draw. Anything above that – something like a 10/3 wire – is simply overkill. This is why we always use a 10/2 wire instead of a 10/3 wire for air conditioners.

Can you use 12 gauge wire on a 30 amp circuit? ›

No. 12 gauge wire is rated for a maximum of 20 amps. You need a minimum of 10AWG wire for 30 amps.

Why does AC have 3 wires? ›

A continuous electrical circuit consists of three wires; a hot wire, a neutral wire, and a ground wire. The electricity will flow through the hot wire into the device you wish to power, or to a receptacle in your home. The electricity then flows back through the neutral wire to complete the circuit.

What do I do if my AC disconnect is neutral? ›

You would just cap the neutral in your disconnect box with a wire nut and leave it disconnected in the main panel. There is no need to switch it and no advantage.

Why does 240 volt not need a neutral? ›

Note: 240V in the US is split-phase and doesn't use the 120V neutral. 240V in the UK is single phase with one live wire, one neutral (and always one earth wire). short answer: it's because the two, 180 degrees out of phase, feed wires essentially take turns being the return wire every time the phase switches.

How many circuits can be on a 100 amp panel? ›

Typical 100-amp panels have 20 circuits, meaning they can handle 20 full-sized breakers. 20/24 panels can hold 16 full-sized and 4 twin breakers (24 circuits in total). The number of breakers can max out to 30-42, too, depending on the design of your 100-amp pane.

What is the 10 foot tap rule? ›

The 10 ft. tap rule states that a cable rated for at least 10% of the rating of the upstream protective device must be used. In this example, we see that multiple taps are used coming from a single circuit breaker as long as all of the taps comply with the NEC requirements.

How far can a disconnect be from a panel? ›

The NEC simply says as close as practical. Some locations do impose an actual distance number. Most areas have a limit of 5-6 feet into the structure to the main panel/disconnect.

What size fuses for 30 amp AC disconnect? ›

Typically, a 30 amp disconnect requires a 20 amp fuse. If you don't use fuses for your switch, make sure to choose the correct size of fuses for your switch.

Do I need a fusible or non fusible disconnect? ›

While both options provide easy access to manually open and close a circuit for various purposes oftentimes fusible switches are chosen for equipment that carries higher loads. For example, many residences make use of non-fusible switches for simple equipment like a water heater.

Can you use a switch as a disconnect? ›

Response: Yes. It is permissible to use a light switch as a disconnecting means if the switch meets the requirements for a disconnecting means found in the National Electrical Code (NEC), NFPA 70-2005.

Where do I mount my AC disconnect? ›

Disconnecting means shall be located within sight from and readily accessible from the air-conditioning or refrigerating equipment. The disconnecting means shall be permitted to be installed on or within the air-conditioning or refrigerating equipment.

How far does a disconnect have to be from a motor? ›

This general rule is that a disconnecting means must be provided in sight from a motor and the driven machinery. Since Article 100 defines the phrase “in sight from,” it is clear that the disconnect, motor and driven machine must be visible from each other and at a distance not exceeding 50 feet.

Does an air compressor need a disconnect? ›

Disconnect generally required is more for safety of someone servicing the equipment to be able to turn the power off and have said disconnect within sight while working and not so much an "emergency disconnect".

How low can a circuit breaker be mounted? ›

The minimum height for a circuit breaker box is 4 feet, though the ideal height is between 5 feet and 6 feet. The maximum height allowed for the circuit breaker box is 6 feet.

What is the maximum height a switch is to be installed above the floor NEC? ›

NEC states that circuit breakers shall be installed so that the center of the grip of the operating handle of the circuit breaker, when in its highest position, will not be more than 6 ft. 7 in. above the floor or working platform.

What is the minimum head room for a service equipment that is 5 feet in height and is operating at 600 volts or less? ›

Headroom. The minimum headroom of working spaces about service equipment, switchboards, panelboards, or motor control centers shall be 6 feet 3 inches (1.91 m).

How do I set working clearance? ›

Process for working clearances
  1. Specifying the requirement for clearance protection. ...
  2. Initiating the clearance. ...
  3. Approving clearance application. ...
  4. Applying and verifying tags. ...
  5. Changing the clearance status to Ready. ...
  6. Subprocess for craft involvement. ...
  7. Preparing for clearance restoration. ...
  8. Approving clearance release.

Which line is bigger liquid or suction? ›

The larger line typically carries a cool gas and is insulated. This is commonly referred to as the suction line, but it is also called the return line or vapor line. The smaller uninsulated line typically carries a warm liquid. It is most often called the liquid line.

What is the clearance of working space for a 277 480 volt panel? ›

For example, a 480Y/277V, three-phase, 4-wire switchboard will be installed in an electrical room. The wall across the aisle from the switchboard is concrete block. Because this wall is considered grounded, Condition 2 applies. The minimum working space depth for this switchboard is 3 feet, 6 inches (see Figure 2).

Will #8 wire carry 50 amps? ›

8 AWG may carry a maximum of 70 Amps in free air, or 50 Amps as part of a 3 conductor cable.

How far can you run 10 2 wire on a 30 amp breaker? ›

Other Things You Need to Consider When Installing a 30 Amp Circuit Breaker. You must also consider the wire length for your 30-amp circuit, in addition to the wire AWG. A maximum length of 150 feet is allowed when using a 10-gauge wire size.

How far can you run 8 gauge wire for 30 amps? ›

For 30 amp service 100 feet away you would need a wire that can handle at least 45 amps. Luckily, the #8 AWG wire has a 50A ampacity. You can use the #8 AWG wire for sub panel 50 feet, 100 feet, and even 150 feet away.

What size wire is needed for a 3 ton AC unit? ›

10 AWG wire has 25A ampacity (above the required minimum of 20.45A). That means that we need to use a 10 AWG wire (or larger) for a 3-ton air conditioner.

How many amps can a 12 2 wire handle? ›

You can use a 20 amp circuit breaker with 12/2 Romex as 12/2 wire is rated for 20 amps.

Can you use 10 gauge wire with a 40 amp breaker? ›

A 40 amp breaker will not sufficiently protect a #10 wire, possibly causing a fire. #8 copper wire is appropriate for a 40 amp breaker. There are things that derate the amount of amperage a wire of a certain gauge can carry without any problems. Over a certain length you will need a bigger gauge wires.

How far can you run 12 2 wire on a 20 amp breaker? ›

You can run a 12 gauge wire up to 70 feet on a 15 amp circuit. That number drops to 50 feet if you run 12 gauge wire on a 20 amp circuit.

What happens if wire gauge is too big? ›

If a wire gauge is “too big” then it is a lot more expensive and is harder to bend, as well as more difficult to attach with wire nuts or to switches. Other than that, not much of anything.

Can 12 2 Romex handle 30 amps? ›

Can You Use a 12-2 AWG for 30 Amps Circuit. Yes, based on the National Electric Code or NEC, you can use 12-2 AWG cables for THHN or THWN-rated wires. These cables are made for general purposes and can hold up to 194 degrees without taking any damage.

Does AC disconnect need neutral? ›

There should be a neutral wire if the unit is Y (or star) connected. If all of the internal parts are only connected line-line (i.e. delta load) there is no need for a neutral as there is no current path through the device to neutral.

Can you connect neutral to ground? ›

Its actually quite easy to do but its not allowed. In most wiring systems, there is one and only one point at which the ground is connected to neutral. it is incorrect and probably outlawed by places conforming to the National Electrical Code in the US to connect ground to neutral at will.

Is RC wire same as C wire? ›

The C and Rc wires are not the same. To install this thermostat you should follow the exact same wiring of the previous thermostat.

Why does AC need a neutral? ›

Without it, there would be no circuit for electricity to flow along and complete its circle back to the power source. Neutral wires are important at every point in your entire electrical system—from when they leave a transformer or fuse box all the way through their journey until they return to the source.

Why does 220v not need a neutral? ›

Why Do 220v Circuits Not Need a Neutral? A 220 volt wiring without neutral isn't a requirement. It's because many appliances that require more voltage than a 110-volt electrical assembly may not need a return path. In comparison, 110-volt loads generally require neutral wires.

Does a disconnect box need to be grounded? ›

Generally the meter box, the disconnect and the main panel all need to be bonded (connected via a ground wire) to the earth ground (one or two buried ground rods or sometimes a buried metal water pipe) through a common ground wire.

Why does 220V have 4 wires? ›

The reason this change was mandated by the National Electrical Code is that the 4-wire setup is inherently safer and better able to prevent electrical shock, which in the case of a 220/240-volt circuit can be fatal.

Why does 220 require two hots and no neutral? ›

So to actually answer your question, the 240 circuit you are curious about only needs 2 hots and no neutral is because it returns its voltage through the opposition on each phase. Some circuits will require a neutral if they have a need for a 120v circuit.

Is there a difference between 220 and 240 volts? ›

In North America, the terms 220V, 230V, and 240V all refer to the same system voltage level. However, 208V refers to a different system voltage level. In North America, the utility companies are required to deliver split phase 240VAC for residential use.

How far does a disconnect have to be from a motor? ›

This general rule is that a disconnecting means must be provided in sight from a motor and the driven machinery. Since Article 100 defines the phrase “in sight from,” it is clear that the disconnect, motor and driven machine must be visible from each other and at a distance not exceeding 50 feet.

Where must a disconnect for an air conditioner be located NEC? ›

Disconnecting means shall be located within sight from and readily accessible from the air-conditioning or refrigerating equipment. The disconnecting means shall be permitted to be installed on or within the air-conditioning or refrigerating equipment.

How high can you mount a disconnect? ›

All switches and circuit breakers must be installed so the center of the grip of the operating handle of the switch or circuit breaker, when in its highest position, isn't more than 6 feet 7 inches above the floor or working platform.

How far can a mini split be from the compressor? ›

So, if necessary, you can locate the outdoor unit as far away as 50 feet (~15 meters [m]) from the indoor evaporator. This makes it possible to cool rooms on the front side of a building house with the compressor in a more advantageous or inconspicuous place on the outside of the building.

How far can a disconnect be from a panel? ›

The NEC simply says as close as practical. Some locations do impose an actual distance number. Most areas have a limit of 5-6 feet into the structure to the main panel/disconnect.

Does disconnect have to be in sight? ›

The disconnecting means shall be within sight of the sign or outline lighting system that it controls. Where the disconnecting means is out of the line of sight from any section that is able to be energized, the disconnecting means shall be capable of being locked in the open position.

How do you determine disconnect size? ›

Now, since they come in staged sizes, the disconnect amperage must be higher than the amperage of your circuit. For example, if you have a 20-amp circuit, you need a 30-amp disconnect. If you have a 40, you need a 60, etc.

Do all AC units need a disconnect? ›

According to trade journal EC&M, the National Electrical Code requires that all HVAC systems have a readily accessible method for disconnecting from electrical power. In most cases, a disconnect switch offers an easy way to remove all power to the device.

What is the minimum depth for working clearance for an AC disconnect? ›

The National Electrical Code® (NEC)® Section 110.26 requires adequate working space for all electrical equipment. NEC Section 110.26(A) requires a clear space at least 30 inches wide and 36 inches deep if the equipment is likely to be worked on while energized.

Can you mount disconnect on AC unit? ›

The disconnect is required to be within sight and readily accessible, according to the National Electrical Code (NEC 440.14). It can be mounted directly on the equipment, but cannot obscure the nameplate or be located on a panel designed for service access.

How much clearance does a disconnect need? ›

There should be at least three to three-and-a-half feet of clearance in front of all electrical disconnects and breaker panels. In fact some employers go so far as to mark off a line on the floor or paint an area.

What is the minimum height of an electrical disconnect? ›

The minimum working space height required for the disconnect switch is 61/2 feet (see Figure 6). The minimum working space height for electrical equipment has not always been 61/2 feet. For many years, the working space height (or headroom) was required to be at least 61/4 feet (or 6 feet, 3 inches).

How far off the floor should a breaker box be? ›

Electrical Panel Placement Restrictions

Other placement provisions include the height of installation. An electrical panel must be installed at least 4 feet off the ground, but cannot be higher than 6 feet. You need to also allow for the panel door to open at least 90 degrees.

How far from the ceiling should a mini split be? ›

The indoor mini split unit should be installed between 4” and 6” from the ceiling according to the experts at PowerSaveAC. If your living room or bedroom has higher ceilings, then measure up from the floor, installing the mini split again in the 4”-6” from the ceiling range.

How long can AC refrigerant lines be? ›

So, you should be good. However, you can't have a single line set more than 75 feet between each air handler and the condenser. If you need more than that, you're going to have to do something else or move your condenser.

Can you put mini split lines in the wall? ›

Mini split refrigerant lines can be run in walls. It is a common practice to hide the refrigerant pipes of mini splits in dry walls for aesthetic purposes. Apart from being more difficult to repair, concealing the refrigerant lines in walls have no impact on the performance of the mini splits.

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