DALI dimmable Luminaires with Class II LED modules: why it is not recommended to use them

In recent months, customer demand for luminaires with Class II LED modules and with DALI dimmers has increased, something which Airfal’s technical department advises against due to the lack of guarantees for their correct use.

To understand better the situation, it is important to know what a Class II luminaire is.

Class II luminaires are characterised by additional safety measures such as double insulation or reinforced insulation. This type of insulation is mainly intended for manual electrical appliances, where extra insulation is required as they are used by people for many day-to-day activities.

Thanks to this double reinforcement, it is not necessary to use a ground connection when installing luminaires with Class II insulation. They do not depend on space conditions, which means a significant saving of time and, above all, of money when installing them.
However for some electrical appliances and installations it is recommended to use Class II insulation, such as lighting in the interior of a swimming pool. However, the use of Class II is not recommended for luminaires with LED modules and DALI dimming.

The elimination of the grounding of the installation can cause various electronic malfunctions and this implies several drawbacks and for that reason Airfal advises against this practice.
In the case of luminaires with LED modules, the reduction of Electromagnetic Interference (EMI) cannot be guaranteed by suppressing the earth connection, so it is not possible to comply with the relevant regulatory requirements. On the other hand, the grounding of LED luminaires ensures that the phenomenon of “LED GLOWING” or ghost lights does not occur. This phenomenon occurs when the luminaire with LED modules continues to emit a residual light when switched off or on standby. In the case of Class II luminaires, it is impossible to guarantee that there will be no “LED GLOWING”.

On the other hand, in the case of transients or voltage/current peaks in the power supply network, the presence of grounding causes the filters of the LED drivers to act by reducing or eliminating them. Without the presence of an earth ground connectionn (Class II), any transient will pass through the driver and reach the LEDs, shortening their life span or even destroying them.
We see in this graph a simple explanation, being the left part without grounding, and the right part with grounding:

On the right-hand side with earth connection the transient arrives much more damped than on the left-hand side without earth connection.

In the case of Class II DALI luminaires, it must be explained that DALI drivers are very sophisticated devices controlled by a small internal computer. The control and regulation of the LEDs is carried out under the supervision of a software integrated in the driver microprocessor.
For the correct operation of these devices, the computer that incorporates it needs to “measure” the reference potential 0. Without grounding, the measurement may be inaccurate, and the dimming may fail or have uncontrolled random effects (Current differences between luminaires, synchronism faults…). We can find cases of correct operation in which regulation problems may appear after some time.

In addition, the standard governing a DALI installation (IEC 62386) specifically specifies the need to have an earth connection to protect the control circuits and drivers, as shown in the following figures:

As stated at the beginning of the article, the lack of guarantees for quality, uninterrupted lighting is the main reason why the installation of Class II, LEDs and DALI dimming is not recommended.