By David Herres
Elevators have become an essential feature of most multistory buildings and are no longer limited only to tall buildings. Elevators provide an accessible and easy means of egress for employees and customers. In certain types of buildings elevators are required by the model building codes or Federal law. When there is an elevator outage for any length of time in a commercial or industrial setting, it is usually a very serious problem because the entire operation can be impacted if not paralyzed altogether. Designers and elevator technicians must have the knowledge and expertise to create, install, and maintain systems that function around the clock for years with minimal interruption.
When a system failure does occur, facility maintenance personnel and/or outside elevator professionals must make repairs quickly and with minimal disruption to workflow and building operations. Where available, onsite electricians may perform initial troubleshooting and evaluation when there is a malfunction. For example, an onsite electrician may verify that there is power to the elevator disconnecting means and perform a visual inspection to ensure that nothing is blocking an elevator door. Typically, there is an elevator company on-call that will dispatch an elevator technician to troubleshoot more complex problems. Elevator maintenance and repair must conform to legal mandates, which vary widely in different states or jurisdictions, so the local situation should be researched and evaluated.
Elevators invariably include robust fail-safe interlock mechanisms that prevent the car from moving if any of a certain class of mechanical failures occur. An example is when a door fails to close securely, or the electrical circuit including the door sensor fails to inform the elevator motion controller that the door is closed. There are shut-down mechanisms for various types of elevators. For example, in a hydraulic (non-cable) elevator, the elevator will shut down when the oil reservoir temperature rises above a specific level.
In any elevator system alteration or repair, there is the potential for introducing unforeseen hazards including electric shock, fire, falling down an elevator shaft and injury due to malfunctioning elevator doors or door interlocks. Any uncontrolled movement of the elevator car can result in serious injury. When working on an elevator, a simple error can have disastrous consequences. Electricians should recognize their limitations and not attempt repairs if they are not trained to work on the elevator system. Safety interlock systems must never be left inoperable when an elevator is in service.
To illustrate, a tragic accident occurred on December 14, 2011 in a Madison Avenue, New York City elevator shaft when without warning an elevator car lurched upward, crushing a 41-year-old advertizing executive, causing her death. A lengthy investigation found the elevator maintenance company at fault because workers disabled the door interlock circuit, a common practice during maintenance, but failed to restore it once the maintenance work was complete.
Virtually all elevators are powered by electric motors. For many years, throughout the first half of the 20th century, DC motors were used exclusively because their speed could be easily and smoothly regulated, an important feature as the car slows approaching a scheduled floor stop. In the 1960’s, variable frequency drives (VFD’s) were developed, permitting smooth speed control for off-the-shelf AC induction motors. Pulse width modulation (PWM) was the method that enabled this speed control by varying the duty cycle rather than the voltage, which would indeed regulate speed but also cause overheating and short motor life. VFD’s also control torque and provide other automatic and manual control via a versatile user interface.
In the event of malfunction such as motor overheating or outright failure, electricians should become adept at diagnosing and repairing VFD’s, which are used in a great many applications including but not at all limited to elevators. Great care must be exercised because these systems usually operate at voltages higher than the usual 240 volts. Also, in opening an enclosure and making electrical measurements, even after the unit is powered down, large electrolytic capacitors that are capable of holding a lethal electrical charge may be encountered. Such work should not be attempted until instruction and training in this area has been completed and workers are aware of all hazards and protective procedures.
Elevator installations must conform to all NEC requirements that were in place at the time of the original construction when the elevator(s) were placed in service. Among the more important tasks of elevator maintenance workers is to examine existing installations to see if they conform to current NEC regulations. Of course, there is no obligation to immediately upgrade every installation as new Code revisions are enacted every three years, but in some cases the NEC will require updates when repairs are made. For example, Article 406 requires GFCI receptacles to be installed when receptacles are replaced in any location where GFCI protection is required by the current code. GFCI protection requirements have been expanded in the 2017 NEC. To learn more about 2017 NEC changes, sign up for a 2017 Code Changes course at jadelearning.com. It is a simple matter to install GFCI receptacles in an elevator pit that was built before they existed, but the 2017 NEC does not permit the required lighting to be connected to the load side of a GFCI receptacle. The 2017 NEC also makes it clear that lighting and receptacles in elevator machine rooms must be on separate branch circuits. Old systems should be reworked to incorporate new requirements where this is feasible.
As in other electrical equipment and installations, new elevators must comply with the current NEC requirements, in this instance Article 620, Elevators, Dumbwaiters, Escalators, Moving Walks, Platform Lifts, and Stairway Chairlifts. Specific elevator rules in Article 620 address dedicated circuits in control and machine rooms, enclosing live parts, guarding of machinery, wiring methods in machine rooms, hoistways, pits and cars, GFCI requirements, and signage.
Elevators must also comply with the general requirements elsewhere in the Code. Examples of important Code-wide mandates are Over-Current Protection, Access and Working Space About Electrical Equipment, Conductor Ampacity, Grounding Requirements and Motor Installations. Keep up with the latest requirements by taking one of our on-line courses on the 2017 NEC.