It is one of the most common modes of transportation, carrying many times the world’s population every month. It is also a very safe way to travel. There is a much better chance of winning the large Euro-Millions prize than of being injured in getting from point A to point B.
For those who cannot guess, all of this is true for lifts (elevators in American English).
Everyone in the industry should be proud of that performance. At the same time, even better performance is possible.
In that spirit, a new standard, EN81-20/50, was published in July 2014. It replaces the old standard, EN 81-1/2+A3, which has been around since 2000. After September 1st 2017, EN81-20/50 will become the only standard in Europe. Until then, both are in force.
Besides safety enhancement, part of the reason for the new standard is that elevators are evolving. At one time, hydraulic or asynchronous motors stored in a machine room were commonly used to power an elevator. Now, more and more compact synchronous motors can be found directly stored in the elevator shaft, providing the power needed for motion from there. This shift in motor location and type has implications for electric devices, embedded variable speed drives and communication.
For contactors and circuit breakers, there are four requirements mandated by the new standard.
1. The first is that components have to follow type 1 coordination in accordance with EN 60947-4-1:2010, 18.104.22.168. This means, any short circuit downstream of the circuit breaker/contactor combination must present no risk for the operator and the installation. However, restarting may require servicing via repair or replacement of the contactor.
2. The new standard calls for an 90%AC-3 / 10%AC-4 Utilization Category mix for the main contactors directly controlling elevator motors. Contactors shall be selected accordingly with motor’s usage, keeping in mind that when a motor starts, a current surge is observed.
So, what does that mean?
a) If the motor starts and runs for a sufficient period of time (e.g. >1 min) when it is stopped, the current to be broken is the nominal current. In this case, the contactor has to be chosen relatively to AC3 utilization category
b) If the motor is used in an inching/jogging manner, the broken current may often be the inrush current, which is more constraining than the nominal current to break. In that case, the contactor must be selected according to AC4 utilization category
c )EN81-20 requires main contactors directly controlling elevator motors to be selected so as to be able to support 90% of AC3 and 10% of AC4 maneuvers. This will ensure an adapted lifetime of the contactor respectively to its use
3. Mirror contacts are compulsory. As specified in EN 60947-4-1:2020 Annex F, a mirror contact is a normally closed auxiliary contact, linked with the main contacts of a contactor such that auxiliary and power contacts can’t be closed simultaneously. Mirror contacts enhance safety, ensuring that contactor’s state is properly transmitted in safety chains.
4. Mechanically linked auxiliary contacts are required for contactors. It ensures that a Normally Opened (NO) and a Normally Closed (NC) auxiliary contact cannot be simultaneously closed or opened. This prevents, again, safety chain errors.
Designing and constructing a modern elevator is a challenge. Ease of use, cost and safety all are important. The new standard can help meet those goals and Schneider Electric is there to provide help and expertise.
For instance, in Schneider Electric’s TeSys D motor starter range, auxiliary contacts and contact blocks are intrinsically compliant with the new standard. They allow monitoring of the state of contactors and can be incorporated into a safety chain, highlighted thanks to a safety red cover accessory.
Specific AC3/AC4 contactor selection with type 1 coordination have also been calculated and are available in our dedicated Control panel Technical guide: How to choose the contactors for elevator machinery.
Besides motor starter selection, this guide contains other useful information such as brake contactor selection, relay and contactors’ recommendations, other Schneider Electric components for elevators.
6 years ago
First of all thanks for this share.
EN 81-20 22.214.171.124.1 reads:
Main contactors directly controlling motors shall, in addition, allow 10 % of starting operations to be made as inching/jogging, i.e. 90 % AC-3 + 10 % AC-4.
The key points here are ‘in addition’ and ‘directly’.
This requirement is an ‘addition’ and it is only for main contactors ‘directly’ controlling motors. So this requirement is not for ‘all’ main contactors.
Directly means: main contactors are directly between the mains power and motor. When contactors ON, motor directly ON and vice versa. Possible cases: AC1 speed direct
control, AC2 speed direct control, star-delta control…
Indirectly means: There is a device between the mains power and motor. So even the main contactors are ON, motor can be OFF. Because this device doesn’t give power to
motor yet. Possible cases: Variable speed drives (VVVF), soft-starters…
In these cases main contactors don’t make or brake motor load/inrush currents.
EN 60947-4-1 Annex I reads:
AC1 contactors for use with semiconductor controlled motor loads
Contactors are often used with semi conductor controllers, starters or drives. Contactors for such applications are not intended to make or break motor load currents
at the stated system voltage.
The intended use is to carry motor currents either on the line or load side of such controllers, and allow the controller to be removed from the line and/or load in
the off condition. A further use is to by-pass controllers, usually for the purpose of reducing thermal losses, in the up-to speed condition. In such applications the
contactors should be so controlled and interlocked so as to prevent them being opened or closed when the load current is present.
When the above conditions are met, the contactors may be chosen according to category AC1.
Can you give us some information about using AC1 category for main contactors (Schneider TeSys D) in lift applications with variable speed drives (VVVF)?
6 years ago
Thank you very much for your comment.
Indeed, in lift application, AC3/AC4 mix is only necessary for contactors directly controlling a motor : this is why, in the guide, 90%AC3/10%AC4 selection is only proposed for contactors directly controlling the motors.
Concerning contactors associated to drives, traditionally proposed selection was AC3. However, standard EN 60947-4-1 Annex I validates use of AC1 contactor if contactor is not actuated when on load.
In our case, we have to distinguish 2 kinds of contactors:
> Upstream contactor, used to disconnect VVVF’s power to enable energy savings: this contactor can be chosen in AC1 as it is not actuated under current. Beware, yet to size it regarding VVVF input current and not motor rating.
> Downstream contactors used for safe stop: depending on safety chain, they may be actuated on load. In that case, we recommend sizing them according to AC3.
Nota: please, note that safety contactors should always be positioned below the drive, to ensure that motor is not powered anymore.
I hope I answered your questions.
6 years ago
Thanks for your answer.
Safe stop case is very rare in a lift life cycle: During inspection control (manually by a person) direcly depending on safety chain, and emergency stop. In all other cases (normal operation) which is probably more than 95% of the lift cycle, contactors will not be actuated on load. Don’t you think AC3 would be overrated?
Maybe an approach could be used similar to “90% AC3 + 10% AC4”. It could be “90% AC1 + 10% AC3”.
Thanks in advance.
6 years ago
When a contactor is directly controlling a motor, AC1 utilization category shall not be used.
5 years ago
Hi, very nice Article shared about Contactors.
4 years ago
that’s useful to know the Motor of lift