Maximum number of CBus units

There was always advice that the cbus network shouldn't have more than 100 units - what will happen when say 102 units are connected? We have a couple of installs at the moment with each just over 100 units, and I'd very much prefer to keep the systems as one network and not split using a bridge.

Will the Toolkit allow us to setup the network with >100 units? If this level a guide based on the max power level of 2000mA to go around the cat5e network?

Thanks

Stephen

 

The recommendation of 100 units is a rule-of-thumb for those instances where you don't want to do the hard work of calculating what the network will actually handle. In practice the units on the network need to be analysed for both their current consumption and their AC Impedance characteristics to make a proper analysis of whether the network will work.

The best way to check whether the network will be viable would be to create a new Toolkit database with the exact mix of products that you intend to use and then click on the Network node for that project. It will show you the electrical characteristics for that network and should warn you if the operating limits are exceeded.

If you intend to go over 100 units then one issue you may run into is the total current consumption may exceed 2A. It is a very bad idea to have more than 2A of power supply on your C-Bus network as the extra current can damage the C-Bus cable in the event of a short circuit and the extra power supplies also affect the AC Impedance characteristics of the network. It also means that if you have an issue with the site then Tech Support will not help you until your network is back within the recommended operating limits.

 

The limit of 100 units is determined by design specification for unit input impedance, and is not a hard and fast rule. If your network consists mostly of basic units such as DIN dimmers and relays, PIR sensors and pushbutton switches, exceeding the 100 units by a few percent should not be an issue. You may need to operate the network without a burden if there are communication problems.

Toolkit should work fine with 102 units (you won't be the first to exceed the 100 unit recommendation).

Of course, you shouldn't design a new installation to have this many units - it's always better to break it into sections if you can and leave some reserve capacity.

Some units, like B&W C-Touch and PAC exhibit a lower input impedance and count as more than one unit, which complicates the calculation, but since there is a reserve capacity with basic units, the limit of 100 units can still be used if these make a small percentage of the units on your network.

The network node view (Go menu) in Toolkit displays statistics for your network based on unit specifications, and can give you an idea of the impedance for your situation. An impedance between 500 and 1000 Ohms is ideal.