Print Page   |   Contact Us   |   Sign In   |   Join
IAEI Magazine
Blog Home All Blogs
Search all posts for:   

 

View all (1101) posts »
 

Disconnecting Means for Motor and Air-conditioning Equipment

Posted By Michael Johnston, Wednesday, January 01, 2003
Updated: Thursday, February 14, 2013

The purpose of electrical codes is practical safe guarding of persons and property from the hazards associated with electricity. Numerous prescriptive requirements address safety from the minimum standpoint. Codes and standards are the minimum rules for electrical safety, so one can easily surmise that for electrical safety one must do at least what is required by the codes.

Many rules in the codes require installation of protective devices and equipment to be in place for the user and occupant long after the final electrical inspection and certificate of occupancy (C of O) is issued. One type of protective equipment for use by the occupant and by service personnel is the disconnecting means required for electric motors and air-conditioning or refrigeration equipment. There are also rules for service disconnects, disconnects for appliances, electric signs, and other equipment throughout electrical codes. This article takes a close look at the minimum requirements for locations of safety disconnects for motors and air-conditioning equipment as specified in NEC Articles 430 and 440.

Photo 1

The primary purpose of the Code is safety. Compliance with minimum Code rules will generally result in an electrical installation that is essentially safe and free from hazards to persons and property. More specific to motors and air-conditioning equipment, the Code requires a necessary safety disconnecting device for workers and building occupants to remove the electrical power during service operations and also to be able to disconnect the equipment in emergency conditions, such as electrical fires or explosions associated with the equipment. With electrical events or problems, such as explosions or mechanical failures, the natural reaction is to disconnect the power as soon as possible. The disconnecting means required for motors and equipment falling under the scope of Articles 430 and 440 are safety disconnects. In the interest of safety for anyone who may need to react swiftly to adverse conditions or situations, electrical design and installation should not take the location of disconnects lightly. In the electrical field it is vital that safety be first priority, always.

Disconnect Locations for Motor Controllers


Figure 1

Article 430 includes the minimum requirements for electrical motors. Provisions for locations of motor disconnects are included in 430.102. There are two components of Section 430.102, the controller in 430.102(A) and the motor in 430.102(B). Let’s look at the controller first. Section 430.102(A) requires a disconnect in sight from the controller and it must disconnect to be located in sight from the controller and it shall disconnect the controller from the source. A closer look at the definition of the term in sight from is in order here; by definition, it means that one component can be seen from the other and the distance between must not exceed 15 m (50 ft). The disconnecting means must be visible from the motor and equipment. Visible through a glass partition or window does not meet the requirements of this section (see figure 1).

Section 430.81 indicates clearly that the controller is the device that starts and stops the motor, by making nd breaking the motor-circuit current. An example of a controller is a combination magnetic motor starter. Controllers require servicing from time to time and the required disconnect is a means of safety for the worker performing those service operations. The disconnect also serves to allow compliance with the general provisions in OSHA 1910.333, one of which requires electrical equipment to be worked on while de-energized. Of course during some troubleshooting and testing procedures, the equipment will be required to be worked while energized, and the qualified service person then must wear the appropriate personal protective equipment to provide a reasonable level of protection should an arc flash or arc blast event occur (see OSHA 1910.335 for additional information about personal protective equipment). Some requirements for disconnecting means locations in the OSHA Standards also are similar to what is required in NEC 430.102 and 440.14 (see OSHA 1910.333) for information about lockout and tagging procedures for safety). This article focuses primarily on the rules of the NEC, but compliance with installation rules found in the Code often results in conformance to OSHA provisions also. Knowledge of all possible applicable standards results in increased safety relative to the electrical installation and also assists with worker safety.

The disconnect ahead of the controller allows safe replacement of overloads, fuses, worn contacts, and so forth. Most individual combination magnetic motor starters or starters that are part of a motor control center include both the controller and the disconnect within the same enclosure. Compliance with 430.102(A) is inherent to these types of combination controllers that include both the disconnect and the controller as an assembly. Disconnects and motor controllers can also be installed as individual units and must be located with respect to the provisions of 430.102(A).

Disconnect for Motor(s) and Driven Machinery


Figure 2

Requirements for the motor and driven machinery disconnect(s) are found in 430.102(B), which stipulates that the disconnecting means to be located within sight from the motor and driven machinery location (see photo 1). The disconnect that is provided to meet the requirements of 430.102(A) can also serve as the disconnect for the motor if it is located within sight from and not at a distance greater than 15 m (50 ft) from the motor and equipment. At least one of these disconnects is required to be readily accessible in accordance with 430.107 (see figure 2).

This disconnect is a safety device and provides reasonable protection for personnel that may be servicing the motor or the equipment driven by the motor. Service personnel are able to visually monitor the safety disconnect when it is located in accordance within the limits of the in-sight-from rule.

Two exceptions permit the motor disconnect required in 430.102(B) to be located out of sight from the motor and driven machinery location. These provisions are worth a closer look as this alternative is limited and has become even more restrictive by recent changes to NEC 2002.

The first exception allows the disconnect to be located remote (out of sight) from the motor and equipment in installations or systems where locating the disconnect in sight from the motor is impracticable or introduces additional increased hazards to persons or property. Although this is generally in the judgment of the AHJ, the revision in this section gives a clearer indication of what is intended by the rule in the first place. Some examples are also provided of situations where the location would be impracticable. This information is helpful to designers as well as installers.


Figure 3

The second exception to this disconnect rule is intended to be applied to industrial installations under controlled conditions: (1) that qualified persons service the installation, and (2) written safety procedures are in place. Another fine print note provides guidance and direction to NFPA 70 E (Standard for Electrical Safety Requirements for Employee Workplaces), which includes information about acceptable lockout/tag out procedures. If the installation can meet the restricted conditions set forth in this exception, the disconnects can be remotely located but must be individually capable of being locked in the open position. The provisions for the locking means must be permanently installed on or at the switch or circuit breaker used as the disconnecting means. Portable types of lockout devices are no longer acceptable under this provision (see figure 3).

Air-conditioning and Refrigeration Disconnecting Means


Photo 2

Requirements for air-conditioning equipment disconnecting means are found in 440.14 and 440.13. The requirements and reasons for the disconnects at air-conditioning and refrigeration equipment are basically the same. The decision whether or not to use the rules in Article 440 rather than Article 430 is related to the type of motor employed within the equipment.

Basically, if the motor or equipment incorporates a hermetic refrigerant motor compressor, then the rules in 440.14 apply. Both types of motors are used with air-conditioning and refrigeration equipment and systems, so it is important to establish which Code article and rules apply for a given installation (see photos 2 and 3).


Photo 3

If the air-conditioning equipment incorporates or is driven by a standard motor, meaning a motor that is not hermetically sealed, then the rules in 430.102 have to be applied. It is helpful to visit the definitions in 440.2 for additional clarification on hermetic refrigerant motor compressors. Section 440.3(A) clearly indicates that if the equipment does not have a hermetic refrigerant motor compressor, then 440 does not apply and reference is made back to Articles 422, 424, or 430 as applicable. An example of refrigeration equipment falling under the scope of Article 430 is the typical fan coil unit installed in a walk-in refrigerator or freezer. The disconnecting means would need to be provided for such equipment in accordance with 430.102 (see photo 4).


Photo 4

If the air-conditioning or refrigeration unit falls under the scope of Article 440, the disconnecting means location requirements of 440.13 or 440.14 would apply.

Cord and Plugs as Disconnects

Section 440.13 includes the disconnect provision for room air-conditioners and similar utilization equipment where cord and plug connection can serve as the required means of disconnect. Section 440.63 places a within-sight-from requirement for the disconnecting means for room air-conditioners, and also requires it to be readily accessible from the unit. Section 440.64 also places length limitations on cords of room air-conditioners that are related to the voltage rating of the unit (see figure 4). For 120-volt room air-conditioners, the length of cord must not be longer than 3.0 m (10 ft); and for 208- or 240-volt rated room air-conditioners, the length of cord is limited to not longer than 1.8 m (6 ft).


Figure 4

Section 440.14 includes the disconnect location requirements for air-conditioning and refrigeration equipment in types other than those that are cord- and plug-connected.

The requirements are relatively straight-forward and simple. The disconnecting means must be located within sight from and also readily accessible from the equipment it supplies (see figure 5). Readily accessible is defined in Article 100 as "Capable of being reached quickly for operation, renewal, or inspections without requiring those to whom ready access is requisite to climb over or remove obstacles or to resort to portable ladders, and so forth.”


Figure 5

It should be clarified that the wording in 440.14 requires ready access from the equipment. This is slightly different and more restrictive than the rules in 430.102. 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). Exception 2 to 404.8(A) relaxes this requirement and allows greater heights to meet the provisions of 440.14 for these types of equipment. Examples of applications using the exception to the height limitations are heat pumps installed in hollow spaces above suspended ceilings. The disconnect is permitted to be installed on or within the equipment; and where it is installed on the equipment, it must not obstruct access panels that are removable for servicing (see photo 5).


Photo 5

Two alternatives are allowed by exception to this basic rule in 440.14. One exception refers to the cord- and plug-connected equipment as specified in 440.13, and the other exception is applicable to controlled conditions in industrial applications. In order to qualify for the alternatives in the exception, the refrigerating or air-conditioning equipment must be essential to an industrial process in a facility that includes conditions of maintenance, and the supervision available to ensure that only qualified persons service the equipment. In these cases, a disconnecting means within sight from the equipment shall not be required. Where the disconnecting means normally required by 440.14 is located remotely from the equipment in accordance with the provisions of the exception, it must capable of being locked in the open position (see figure 6).

Summary


Figure 6

It is best in electrical design to start with the rules and not the exceptions. It seems as though over several code cycles, the alternatives allowed by the exception to the required disconnecting means for motors and air-conditioning equipment have been incorporated into design. These disconnects ensure safety for personnel and property, and should not be eliminated for reasons other than those specifically included by the exception to the main rule. Some requirements in the OSHA Standards also are similar to what is required in NEC 430.102 and 440.14 [see OSHA 1910.333 for additional information]. Always consult the local AHJ if there are any doubts or if there are any local codes or regulations that require clarification.


Read more by Michael Johnston

Tags:  Featured  January-February 2003 

Share |
Permalink | Comments (0)