Z-Wave Vs MODBUS / CBUS System – A Design Architecture Perspective

As Smart Home Automation technology is taking the market at large in the UAE and around the world, it becomes imperative to understand the different options in terms of technology architecture as this can save a real estate owner from venturing into an investment that will cost them more to maintain than any form of Return on Investment from the solution.

This document is dedicated to compare the design architecture of Z-Wave against MODBUS or CBUS based systems. Features or detailed specs about the protocols will not be discussed as the difference in design architecture between these protocols and their components may be more than enough in order to make a decision on what technology can give the greatest investment protection.

Design architecture in this document will refer to the interconnections at the level of lighting circuits. In very basic form, and in a normal house that does not have any Smart Home capabilities, a ceiling light would be connected in series with a light switch and the electrical distribution board (DB). The 220V line would start at the electrical DB, enter a standard relay, go to a junction box where a standard light switch is connected, then from the junction box to the ceiling light and back to the Electrical DB's neutral connection.

Z-Wave network architecture is exactly the same as the standard connection described above, and that is why Z-Wave systems can be retro-fit into any existing home. In order to install this system, all what is required is to replace the standard lighting switch in the junction box with a Z-Wave enabled light switch. All other remaining connections to the DB and to the ceiling light remain un-touched.

All the intelligence lies in the wireless switch installed in the junction box. A Smart Home server or controller will then have to send commands wirelessly to that switch to turn "ON", "OFF", or "DIM" the lights.

MODBUS or CBUS based systems on the other hand, use a completely different architecture which is non-standard in comparison with the standard home lighting system (described first in this document). In MODBUS or CBUC systems, the connections between the DB and the ceiling lights, and between the DB and the junction box (wall switch) are completely separate. In addition, there are no connections between the Junction Box and the respective ceiling lights. The Intelligence of a MODBUS or CBUS system lies in a "Channel Dimmer" or "Channel Relay" which is installed in the DB and would replace the traditional standard relay installed in existing homes today. This "Channel Dimmer" would have a 220V Line interconnection directly to the ceiling light and a neutral connection back from the ceiling light to the "Channel Dimmer". The "Channel Dimmer" will control the light directly and will receive its commands either from a rail mounted controller that is connected to its communication port (could be a serial port), or manually from a wall mounted light switch / keypad. This wall mounted light switch would not be connected to any load whatsoever, it would be directly connected with the "Channel Dimmer" by means of a control / signaling cable. The "Channel Dimmers" normally come as 4-channel or 8-channel, this means that they can be connected to 4 or 8 separate lighting circuits at the same time and this din-rail mounted device is also a single point of failure for all these 4 or 8 lighting circuits.


Now that the design architectures have been explained, we jump to comparing their advantages and disadvantages to the real estate owner. It is clear that MODBUS or CBUS based systems do not have standard interconnections between lighting circuits and junction boxes (wall switches), and thus these systems must be installed during construction phase in order to ensure the correct wiring between the Channel Dimmers and Lights, and between the Channel Dimmers and Wall Switches. But this imposes a great risk to any home, that is, in the event that the Channel Dimmer fails, an entire group of lighting circuits would fail (For example: In all bedrooms on the second floor). Further to that, and in the event of failure, no standard electrician will be able to fix the problem and the home owner would be stuck waiting on the company that installed the system to order, deliver, and install the Channel Dimmers; a process which may take weeks. And finally in a worst case scenario, what is the Channel Dimmer fails after 5 years and the technology becomes obsolete, or the company which is providing maintenance closed down? In that case, the home owner would be left with 2 options, either to find a similar technology from a competitor, which will require a complete re-installation of the entire system including the controllers, touchscreens … etc. Or the home owner can revert back to the standard lighting system that is not a "Smart Home", but in order to do that, the entire house would have to be rewired; a project that would take weeks rendering the house in an un-livable condition until competition, not to forget the cost of having to run such a project potentially leading to loss on the Investment made on the Smart Home system to begin with.

Let us look at the same scenario from the Z-Wave system's perspective. A Z-Wave system only requires replacement of a wall switch with a Z-Wave enabled wall switch on a standard electrical wiring system. So in the event that a Z-Wave light switch fails, only one lighting circuit (ceiling light) would be affected. Further to that, what would be required is a simple replacement of the light switch. Considering an even worse case scenario, where a Z-Wave light switch fails after 5 years and the company which provides these light switches had closed down and the home owner would be left with no choice but to revert back to the standard none "Smart Home "system or wait a week's time to order a replacement. In such a case, all that is required is to replace the failed Z-Wave light switch with a single standard wall switch, no re-wiring nor complex installation is required and any electrician can do the job. The home owner can probably do it himself / herself! It is important to note that in such a worst case scenario, the situation can be relieved with ease and with the services of any available electrician who does not necessarily know anything about Smart Homes. Whereas MODBUS or CBUS would require a professional trained on those wired systems to handle much more complex work, impacting time, and cost for any kind of maintenance, be it major or minor.