A comparison between C-BUS and Z-Wave - Part 1
(C-BUS VS Z-Wave)
Smartest Home is a leading home automation company providing home automation solution and products to customers across Australia.
In this article we are trying to compare the C-Bus and Z-Wave protocols and network topology briefly.
C-Bus is created and developed by Clipsal in Australia (now part of Schneider Electric) for smart home and it is mostly used in Australia, New Zealand, and spreading through Asia, the Middle East, Russia, South Africa, the UK and other parts of Europe.
C-Bus communications protocol is based on a seven layer OSI model for smart home and building automation and can handle cable lengths up to 1000 meters using Cat-5 cable.
In general a C-Bus network includes a C-Bus Automation Controller, Input units, Output units, Accessories and Software.
Clipsal recommends a special purple Unshielded Twisted Pair Cat-5 cable and connectors to be used to connect the devices. The acceptable network topology is star and daisy chain and maximum cable length is 1km. Loop topology is not allowed in C-Bus network.
The standard C-Bus network voltage is 34 V DC and Schneider electric recommends 22 V DC as the minimum voltage on the network.
All C-Bus output units consist of electronic components that can be damaged by surges, short circuits, and overvoltage conditions. Schneider electric recommends using overvoltage protection in the main breaker panel. If the C-Bus Cat-5 cable is routed between buildings or used in an outdoor installation, also use overvoltage protection on the C-Bus cable.
Each C-Bus network requires at least one system clock generating unit for data synchronisation.
C-Bus allows 255 network in one installation this limitation does not apply if a C-Bus Ethernet Interface is utilised, the system size is then limited to IP Addressing only. The maximum number of networks connected in series to the local network via Network Bridges is seven (i.e. using six network bridges).
A typical C-Bus network is shown in the above diagram from Schneider electric website.
Many C-Bus units have connections to Class 1 (240 V AC) and Class 2 (15–36 V DC C-Bus) rated wires. Special care must be taken to allow separation between class 1 and class 2 cables to avoid noise and interference.
Clipsal recently has introduced a wireless gateway to allow connection between wired and wireless networks. While the gateway allows the wireless devices to communicate with the C-Bus network it does not eliminate the centralised load control wiring and the wireless devices need battery to operate.
A typical wireless network is shown in the above figure from the Schneider eclectic documents.The C-Bus Wireless Gateway itself is powered from the wired C-Bus network via an RJ45 connection.
An example of a C-Bus control smart home control panel from Schneider electric documents is shown below:
As it can be seen C-BUS does not follow the conventional wiring schemes.
In conventional wiring, the mains power is connected through a distribution board (DB) to the load via a wall switch (Below picture ).
In the C-BUS system the power control (Dimmer or Relay) is installed in a distributed panel and completely separated from the control units like the wall switch. The wall switch is not connected to any load whatsoever. The dimmer or relay module in the control panel receives the command from the wall switch or any other device on the C-BUS network. This topology requires a centralized panel or multiple local panels which are connected to the loads while the control units like wall mounted switche or sensors are sending the command signals though the C-BUS network to the same control panel (Below picture).
While C-BUS has proved itself as one of the key players in the Smart Home industry it has the following cons:
1- Although it’s been opened by Schneider electric for the other manufacturers to develop C-BUS products it is still very well dependent on Clipsal products.
2- It does not follow conventional wiring schemes.
3- Special wiring and network separation requires special electrical design.
4- It requires two separate network wiring which increases the cost of installation.
5- C-BUS products are generally more expensive in comparison with Z-Wave products.
In part two of this article we will be looking at the Z-Wave protocol characteristics.
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