Category Archives: KNX

KNX-Lighting Control Part 2

Lighting and KNX control.

In a previous blog I discussed the advantage of using KNX for the lighting control only.  Some of the KNX control options are expensive so in order to keep things simple and affordable I have decided to use the following devices to control the lighting.  As most of the LED lights are using around 5 Watts of power I will also eliminate the dimming functions and ensure that the layout of the lights in the ceiling can be switched on separate circuits in the larger rooms (a simple form of dimming in a way).

Universal Interface

The hardware required will be a KNX binary input /output device  with 12 inputs/outputs to connect to standard light switches. The advantage is that the cost is reduced by not using a special KNX light switch.  A single KNX switch can cost up to €100 while a simple mechanical switch that costs €2 or €4 approximately can carry out most of the primary switching functions and is designed to work on the KNX system.

My preference and research on the best value for money is a product made by ABB called an Universal Interface US/U 12.2 . Expect to pay around €120 for one of these  which has 12 inputs/outputs (Equates to €12 euro per room). It can also carry out dimming control with a suitable KNX actuator (device that switches the power from a central distribution location). There are numerous other functions built in that are relevant to lighting and indication control.

Universal Interface
EIN KNX Interface

The plan is to mount one of these Universal Interfaces in 4 different areas in the house (The size of one of these units is approximately 52mm in diameter) .  A maximum of 12 light switches will connect to this Universal Interface. It is recommended to keep the cable feeding the light switches to a maximum length of 10 meters (although I have found it works reliably up to 100 meters). I will be using screened alarm cable (6 core) to each of the switches. In this way I plan to leave a spare core for each switch so that other functions can be applied in the future without re-decorating.  I will be using a push to make light switch as this allows one to use the same pair of cables for two way control and optimise the use of the cores in the cable.

Each 12 channel Universal Interface will have its own  KNX 12 channel switch actuator ( see below-it can control 12 different lights using 230 volt power in the building) that will switch the LED lights. One location to source these is http://www.eibmarkt.com

Switch Actuator

For the switch actuator (relay control of the lights) one can select the equivalent 12 channel KNX actuator. If one goes to the above web site or other KNX web sites and enters EIB KNX switch actuator 12-fold, SA.12.16  in the search engine one will find these units. Expect to pay around €230 for one. If one goes to http://www.eibmarket.com they have one for around €239 including VAT.  This works out at a cost of around €20 per room along with the savings in wiring and flexibility in the future as discussed in the previous blog.

actuator

Dimming Option

If one wants to dim LED lights one needs to research a suitable dimmer for the LED light. There  are different technologies used to dim LED lights so one needs to establish which LED lights to use first before committing to purchasing a dimming function. I am aware of two types such as leading edge and trailing edge controls for dimming.  As I will not be dimming the low wattage lights a simple actuator is all that is required.

Wiring System (Lighting)

Lighting Control System

For the electrical wiring I plan to use a central control system called KNX for the lighting  ( I will build in the flexibility to control power outlets from the switch positions in the future) . What this means is that the power for the lights will come from a central fuse/distribution board and the switches for the lighting will be independently controlled by an extra low voltage.

The reasons for selecting this KNX control system are:

  • to reduce the impact of interfering with the airtight envelope (as the cable is similar to alarm cable thus less wiring will need to be installed and more room functions can be carried out with one cable).
  • Extra capacity can easily be included in each switch position in order to allow for wiring changes in the future. (If a new light needs to be controlled from an existing switch no modification of the wiring, internal wall/ceiling structure or room re-decoration needs to take place).
  • Because the voltage is very low and DC (Direct Current) it will reduce electrical and magnetic fields and minimize the use of 230 volts AC (Alternating Current) from a health perspective.
  • Possible to use extra functionality already available in KNX such as timers/power down control (did you ever have an ESB power failure and one had to leave the house before power was restored only to find when you came back that items were left on such as lights or hairdryers etc.-with the KNX system one can configure the system to return everything to the off position when power is restored.)
  • When leaving the house one switch can be configured to turn off all the lights or turn on essential lights.

I became a KNX partner in order to purchase the software to design and develop a prototype before the build. There are other building control systems and smart systems but the KNX system is a world standard and an open standard for commercial and domestic building control. Most of the large electrical companies manufacture  KNX products.

While the KNX system can manage the most complex building and smart home systems I will be using the most basic functions of the KNX system in order to keep costs under control and make use of the benefits as outlined above.

The sketch shown below might help to explain the difference between a standard wiring system and a KNX system.

Standard Wiring
Standard Wiring-230 Volts power cable at all light switches
KNX
KNX System-No direct connection from the switch to the light