Secondary power supplies for emergency evacuation lifts

Power Control
23 Apr 2019

UPS systems used to support emergency systems such as evacuation lifts must comply with BS EN 50171 regulation.

Uninterruptible Power Supplies (UPS) are often overlooked as a backup supply of power for evacuation lifts as they usually evoke images of large data centres and IT infrastructure. However, in order for a premises to comply with BS 9999 regulation, there must be a secondary source of power feeding all evacuation lifts. In many cases, providing a secondary mains feed simply isn’t possible, so a UPS system and or generator combination is used instead.

When an authorised person is present, emergency lifts provide an evacuation route for disabled persons in the event of a power outage. During normal operating conditions they should be available as a passenger lift and not solely for evacuation or an occasional use of transporting goods.

Where a generator is being used as the secondary supply in a hospital for example, a UPS system must also be present. A factor often overlooked by building management. This is to meet regulations stating that healthcare facilities must test their emergency generators under load at least once per month for 30 minutes, not including the warm-up and cool-down time. During this period only one supply of power would be supporting the lift, if this was to be disrupted then the lifts would not be operational.

In other circumstances, a UPS system is preferable as it is easier to install into the lift plant room, often located at the top of the lift chassis. The logistics associated with installing a generator onto the top floor of a high rise building can be costly and the space saving benefits of a UPS appeal to building managers.

These backup power supplies must operate the lift for either 60 minutes or 3 hours depending on the evacuation plan and whether immediate evacuation of the premises is possible. For example, hospitals and care homes require a longer evacuation process and so would need backup power for at least 3 hours.

The evacuation lift must be provided with communication networks from the plant room to the lift car and the main floor. It’s recommended that the lift control panel is also fitted with a smaller single phase UPS to resume communication during a power outage. The plant room typically requires a standalone three phase UPS system compliant with BS EN 50171 standard to provide backup power to the lift motor.

Furthermore, it is recommended that a variable speed drive (VSD) is considered at the time of install. This negates the need for an oversized system to cope with the inrush current which is often 8x or 9x the running current. Fitted in between the UPS and lift motor, a VSD limits this inrush of electricity to 1x the running current, softening the initial start-up and not affecting the overall supply.

Also to be aware of is the potential risk of a regenerative load, a common occurrence with lifts when the UPS has no load from other equipment. The lift motor can become a generator and feed power in the wrong direction. Most lifts are sufficiently counter weighted to minimise this effect but a load bank is still recommended by UPS specifiers and installers.

Depending on the size of the premises and the number of lifts requiring support, a three phase UPS of 10kVA to 160kVA capacity is sufficient to replicate the mains supply normally serving the lift. Providing the ability to run the lift at normal speed and sufficient capacity to complete a required number of journeys, meeting BS 9999 regulations.

for specific emergency backup power product information or email Power Control’s Divisional Sales director