During a training session on the National Electrical Code, a question came up about motor disconnects. The variety of responses inspired this article. The initial question was, “Are all disconnecting means for motors required to be capable of being locked in the open position?” The answer is no; however, many knife switches and other types of equipment disconnecting means are manufactured with a locking provision that is an inherent part of the disconnecting means enclosure. Their benefits are that operators and other personnel can remove the power and install their lock to ensure an electrically safe work condition at the motor and driven machinery location. 

The purpose of the means to disconnect the motor power is twofold. First, creating an electrically safe work condition eliminates shock and electrocution hazards. Secondly, putting the disconnect in the open (off) position and locked keeps driven machinery from starting and creating mechanical and bodily injury to operators or workers servicing the motor or machinery. 

Precise requirements

NEC requirements align with and complement the requirements in Article 120 and Section 110.2 of NFPA 70E, Standard for Electrical Safety in the Workplace. The hazards covered in the scope of NFPA 70E are electric shock, arc flash and arc blast. The NEC requirements for motor disconnects are more detailed on disconnecting means locations relative to the actual motor and driven machine location.

The Code rules for motor disconnects are in Part IX of Article 430. The rules address disconnecting means location, types of disconnects, capacity and group installations served by a single disconnecting means. 

Generally, the disconnecting means must be capable of disconnecting the motor(s) and motor controller(s) from the circuit. Section 430.102 spells out the disconnect location requirements for the motor controller and the motor itself. 

Section 430.102(A) is clear that a disconnecting means is required for each motor controller and must disconnect power to it. This disconnect generally must also be located in sight from the motor controller location. “In sight from” is defined in Article 100 and described in Section 110.29. 

Any use of the terms “in sight from,” “within sight of” or “within sight from” means that the equipment (motors in here) must be visible and must not exceed a distance of 15 m (50 feet) from the disconnecting means. 

It is important and interesting to note that Section 430.107 requires at least one of the disconnecting means addressed in 430.102(A) and (B) must be “readily accessible” as applied to equipment. Exceptions to this controller disconnecting means location are for motor circuits over 1,000V, for a single disconnect ahead of a group of coordinated enclosures and for valve actuator motor assemblies that contain the controller. See Exception Nos. 1–3 to 430.102(A). 

Section 430.102(B) generally requires a disconnecting means to be in sight from the motor and driven machinery location. The disconnecting means required for the controller can also serve as the required motor and driven machinery disconnect, provided it meets the “in sight from” criteria for both. 

The exception to 430.102(B) relaxes the “in sight from” requirement for the disconnecting means. It allows for remote disconnecting means able to be locked in the open (off) position under these conditions:

(1) The location of the motor disconnecting means is impracticable or introduces additional or increased hazards, or

(2) Disconnecting means for industrial processes with written safety procedures if conditions of maintenance and supervision ensure that only qualified persons service the installation.

“Qualified person(s)” is defined in Article 100 of the NEC and NFPA 70E. 

Ensure such out-of-sight disconnecting means meet all requirements in Section 110.25. This signifies that the disconnecting means must be capable of being locked in the open (off) position, and the provisions for locking it open must remain in place with or without the lock installed. Disconnecting means that have inherent lockout capabilities meet this requirement. 

There is also accessory-type equipment that can be applied to switches and circuit breakers if they do not have inherent locking means provided by the manufacturer. Remember that this requirement applies to each disconnect, switch or circuit breaker. Compliance with this rule is not achieved by only locking a switchboard or panelboard door or a door to an electrical room.

michael johnston