How Do Emergency Brakes Work with UCMP?

How Do Emergency Brakes Work with UCMP?

UCMP Educational Series – Part 4 of 6

In the last post, we looked at why Unintended Car Movement Protection (UCMP) was added to the code. One of the key points was that UCMP provides a backup to the machine brake if it fails or cannot hold the cab in place. That backup comes in the form of an emergency brake.

Unlike the machine brake, which is used during normal operation to hold a stopped car at each floor (and for older elevators, such as single-speed units, to slow the car down), the emergency brake is only intended to activate under fault conditions. As outlined in ASME A17.3 Section 3.8.5.1, these include ascending car overspeed, unintended car movement, or decelerating the car to rated buffer speed. When UCMP detects unintended movement with the doors open, the emergency brake engages to stop the car quickly and safely.

For retrofitting an emergency brake for an existing elevator, we get our requirements from ASME A17.3 Section 3.8.5.2. A summary of the emergency brake requirements:

• Act on a critical moving part – It can apply braking force to the car, counterweight, suspension means, compensation means, drive sheave, or brake drum.
• Be independent of the machine brake – It cannot share parts with the primary brake, ensuring it works even if the machine brake fails.
• Operate only in emergencies – It is not used in day-to-day automatic operation, only in the case of UCM, overspeed conditions, or other emergencies.
• Control deceleration safely – It must not exceed 9.81 m/s² (32.2 ft/s²), preventing passenger injury during stopping.
• Meet defined safety factors – The brake and its parts must be strong enough to function under maximum loads and wear conditions.
• Be fail-safe – It cannot require electrical power to apply, so it activates during a power removal or loss.
• Be identifiable and serviceable – If field adjustment or servicing is required, it must be marked with a permanent “EMERGENCY BRAKE” label.

Commercially, there are many types of brakes that fulfill these purposes: rope brakes, disc brakes, drum brakes, plate brakes, and other braking methods that meet the above criteria. Each has its own advantages and disadvantages in installation, braking ability, and maintenance.

In the next post, we will look at how to determine if your elevator already has UCMP installed and what indicators to check to ensure your system is compliant.