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Elevator and Escalator Consulting Engineers

Elevators with Single Speed AC Motors - Upgrade

Information Bulletin – Owner Update 2014-06

Single-Speed Elevators


Single speed elevators are commonly found in residential buildings of up to four or five floors in height. These elevators are difficult to adjust to level at each floor within the tolerances allowed by the code and expected by elevator passengers.

Ontario has mandated a timeline for replacement of single speed elevators.  We anticipate that the other various authorities having jurisdiction will require owners to improve the levelling of these elevators within the next few years. Practically speaking this will require a modernization of the elevator control systems to ensure accurate levelling and re-levelling at each floor. 
We also understand the various jurisdictions are considering a similar legislative approach for elevators with two-speed alternating current motors.  The number of devices, and consequently number of building owners affected, will be more significant if these elevators are mandated for upgrade.

KJA recommends you review your portfolio for elevators with single-speed and two-speed motors and budget for modernization in accordance with the schedule issued by the TSSA.

Useful Links:

The Technical Standards and Safety Authority (TSSA) have issued a Director's Order outlining their legislative timelines for Ontario. 


Background and Technical Information:

Just after the Second World War the City of New York in conjunction with the federal government launched a redevelopment project in the Hells's Kitchen area of New York City to provide low-cost housing for those workers at the low end of the economic spectrum. At the time, Hell's Kitchen had a gritty reputation. Today, because of its proximity to the Manhattan core and because of upgrading by more affluent members of society it has become a desirable residential location.

In the 1950's, the housing development centred around low-rise rental units and for these units Otis developed an elevator using a low-cost machine - a machine known as the 14AT. This machine used a single-speed alternating current motor. In effect, it was probably the simplest form of elevator design. The 14AT proved to be quite profitable and competitive. Given the success achieved in Hell's Kitchen, Otis expanded the sales of the 14AT so as to be able to compete in the market for low rise rental buildings. Many of these units were sold. In Canada, Robert Lindegger of Horn Elevator (later Northern Elevator which was subsequently purchased by ThyssenKrupp) developed a competitive design that, when marketed head-to-head with the Otis product, captured the majority of the work. Ultimately, a significant number of single-speed AC elevators were installed across Canada – particularly in Ontario.
This type of elevator, although cost-effective, suffers from one major drawback: it does not level well. Which means that even when well-adjusted and maintained the difference between the cab floor level and the entrance floor level with the elevator stopped at the floor may be in excess of three-quarters of an inch (19 mm). This is enough to represent a tripping hazard to people who are accustomed to the more precise levelling obtained by modern elevators.
It helps to appreciate the task that the maintenance contractor faces if you have an understanding of the basics of this type of elevator. In a general way, this elevator is like an automobile with two speeds: go and stop. If the auto has a constant load, say one passenger, then the brakes can be adjusted so that when the power is removed and the brake applied (these two events happen at the same time on this type of elevator), the automobile will stop in some given distance - say six inches (150 mm). But if there are two passengers, then the automobile may stop in twelve inches (300 mm). This does not matter much with automobiles but does with elevators.
There are two ways of minimizing the problem: a sharper braking action and a greater 'base' load. So we can crank up the brake so that with one passenger the auto stops in three inches (75 mm) and in four inches (100 mm) with two passengers. If we change the 'base' load by adding weight in the trunk of the car we can also reduce the variation in stopping distance. With elevators, there are limits to how sharply we can brake without causing complaints or without injuring fragile passengers.
The Northern product has an oversize motor-gear brake coupling which adds mechanical inertia to the drive (effectively increasing the 'base' load). This means that variations in load - more or fewer passengers - have less effect on the stopping accuracy. So a Northern single-speed AC elevator should be able to level within plus or minus three-quarters of an inch (19 mm) consistently. This accuracy is difficult to obtain consistently with the 14AT. In any case, both the Otis and Northern product do not consistently meet the desired levelling accuracy of 0.5 inches (13 mm).
For this reason, the safety authorities in various jurisdictions are considering mandating the replacement or modernization of these units.  Before the building owner or manager has to deal with the replacement of the existing single-speed AC elevators, there probably will be a grace period of several years. But it is desirable to be cognizant of and budget for this capital expense.

In the interim, it is wise to pay careful attention to the maintenance and adjustment of any single-speed units that are under your management.