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Best Practice: Upgrade of Single Speed AC Elevators

D&D Elevator on Wednesday, March 20, 2019 at 12:00:00 am 

A typical single-speed, AC traction motor


A typical single-speed, AC traction motor

Building owners and managers whose properties continue to operate Single Speed AC traction elevators should seriously consider upgrading their equipment to modern standards, and there are many good reasons why. Continued operation of this outdated technology presents many problems: code compliance issues, ongoing repair costs, insurance costs, risk of downtime, but, above all – because of their inherent leveling issues – discomfort and risks to passengers and exposure to consequent trip-and-fall litigation.

Single-speed AC (SSAC) electric traction elevators are slow speed, low-capacity passenger units that may cause the elevator not to stop within level. They first appeared during the post-World War II period, often installed as upgrades to earlier, prevalent DC systems as the municipal trolley grids that powered them became extinct, with installation continuing into the 1970s. Popular because they were attractively priced, they typically appeared in low- to mid-rise residential buildings, including condo conversions and rental apartments.

These elevators travel at one speed, which makes them prone to intermittent leveling fluctuations and trip-and-fall trip hazards, particularly to elderly passengers and those with mobility disabilities who may find it extremely difficult to negotiate level differences. These elevators are now obsolete and no longer made or installed. Current New York State code requires that elevators, when arriving at a floor, stop accurately and consistently within a finite limit of ½-inch above or below floor level. This is reflected in the current edition of The American Harmonized Elevator code (CSA B44/ASME A17.1). The Technical Standards & Safety Authority (TSSA) has also written on the matter, that these elevators, because of their poor leveling ability, should be upgraded.

SSAC elevator hazard









Due to the imprecise braking on this SSAC elevator, it has stopped well above the code-mandated tolerance of ½-inch above or below the floor, which can cause a hazard to passengers and the risk of trip-and-fall litigation

SSAC elevators relied on brakes to stop the car in properly level position, which often proved imprecise and inaccurate. Conversely, today’s elevators have abandoned the use of brakes to stop the car, instead employing variable voltage-variable frequency control systems that consistently stop the elevator at floor level within tolerances of ¼-inch. As their name implies, these adjust both the voltage and frequency of the power applied to the hoist motor, thereby varying the speed at which the motor operates. With this technology, the hoist motor can be brought to a so-called “electrical stop” – with the hoist motor energized but not turning. This allows floor stops to be accurately specified, without regard to the load in the car.

The experts at D&D Elevator stand ready to help you evaluate your particular needs, to cost-efficiently achieve code-compliance, safety – and peace-of-mind!