Why Should My AC Have a Safety Disconnect? 

National Standards

The first point to understand about any industry in America, and specifically the High Velocity Air Conditioning and Heating industry is there are departments and selected groups that set the standards for installation, sales, and maintenance. Each area of concern is addressed by these governing bodies to provide a standard of manufacturing and a degree of safety for the installer and the homeowner. These highly skilled bodies must not be seen as problems that complicate the industry, but must be viewed as safe-keepers with only the general public’s well being in mind. Therefore, adhering to and abiding by the standards and laws as set forth by these governing bodies is, at minimum what each HVAC installer should be pleased to do.

One of the governing bodies within the field of HVAC is the National Electric Safety Code(NESC). This code creates and sets the ground rules for safeguarding of individuals involved with installation, operation, and maintenance of power, telephone, cable TV, and railroad signal systems. The NESC also involves itself in work rules for construction, maintenance, and operation of electric supply and communication lines and equipment. It is a safety reference for HVAC companies across the USA. It is important to note that the NESC gains information and is impacted by the National Fire Protection Association(NFPA) and the Occupational Safety and Health Administration(OSHA).

Specific Codes

Article 440 of the National Electric Safety Code provides guidelines and standards for electrically driven air conditioning and refrigeration equipment. It also provides the standard for machines and technologies that  contain a hermetic refrigerant motor compressor which is a combination consisting of a compressor and motor enclosed in the same housing.

This section of the NESC requires the disconnect to be within sight of and readily accessible from the air conditioning equipment. The idea of “within sight” specifically means visible from and not more than 50 feet from the outside compressor unit. The disconnect may be installed on or within the air conditioning equipment but not on the access panels.

This disconnect article section also provides standards for the circuitry related to the air conditioning equipment. Safety disconnects are sometimes not fused. However, sizing and type of short-circuit and ground-fault protection devices is indicated on nameplates in or on the AC equipment. The manufacturer of the AC unit calculates ratings. If the nameplate states “HACR Circuit Breaker,” then an HACR-rated circuit breaker must be used. If the nameplate states “Maximum Fuse Size,” then the installer must use a one-time or dual-element fuse.

Within the field of electrical engineering a disconnector switch is used to make sure an electrical circuit is completely interrupted or de-energized. High voltage isolation switches are used in electrical circuitry to allow for the isolation of circuit breakers, transformers, and the lines through which electricity is sent. The interrupter or disconnect is not needed for daily operation of the circuitry, but is used in the case of emergencies or maintenance. Disconnectors are not designed to suppress electric current or decrease its capacitance. A switch disconnector combines the properties of the disconnector and a load switch. It provides a safety isolation functionality and can break nominal currents.

HVAC disconnects can be fusible or non-fusible. To determine your disconnect type, pull the handle of the cover and look at the back of the box. A fusible will have up to 2- 30 amp cartridge fuses.  Fuses are needed for overload protection in relationship to the motor size inside the HVAC unit. The fuse is sized to the motor and may or may not be a different size than the main circuit breaker inside your home.

A fusible disconnect provides for the following:

  • Protection against overcurrent
  • Protection against short circuiting
  • Protection against heat generated damage
  • Protection against circuit overloads

A non-fusible disconnect will have copper bars that allow voltage to pass.

An acceptable enclosure for the disconnect meets the requirements of the NESC. It must be a rainproof enclosure that can withstand the outdoor environment. It should be fitted with a means to use a padlock. It should also have a two position pullout handle. Various corrosion free models are available.

So, Why the Disconnect?

There are, essentially two reasons to have a disconnect located near the outside unit. The first reason is to provide a measure of safety for a service person. It may not be understood by some inhabitants of the dwelling that someone is working on the AC unit outside. They may discover the inside breaker off and turn it back on, thus sending to much voltage to the AC unit when the service person is thinking they are safe. Also, service personnel may need to switch power on and off during repair or maintenance to determine if the unit is functional. It is convenient to do this using the disconnect box nearby.

Secondly, accidents do happen. In regard to HVAC units electrical fires and explosions can happen. During these events, the natural and smartest reaction is to disconnect the power as soon as possible. If first responders are called, they may not be able to enter a dwelling or building to disconnect power. A disconnect outside and near the unit is wise and useful for everyone concerned.

Should you find yourself in need of a safety disconnect or your present disconnect is in need of maintenance, then call Freedom Heating and Cooling at 205-444-4444.