Device Loading - Distech Controls ECL/ECB-PTU Series User Manual

Device Loading

Each device presents an electrical load on the BACnet MS/TP Data Bus Segment. This is
called device loading. The use of full load devices limits the number of devices connected to a
BACnet MS/TP Data Bus Segment to 32 devices. Distech Controls' BACnet MS/TP devices
are ⅛-load devices and ½-load devices, which allows more devices to be connected to the
BACnet MS/TP Data Bus Segment, as compared to full load devices.
Table 3: Device Loading
Manufacturer
Distech Controls' ECB controllers
Distech Controls' ECB-PTU Line-Powered
Controllers
Distech Controls' BACnet MS/TP Thermostats
Other manufacturers
However, if a data bus segment is interoperating with devices that are full-load, ½-load, ¼-
load, or ⅛-load, then the device that supports the fewest devices on the same data bus is the
one that sets the limit for the maximum total number of devices for that data bus segment. For
example, you plan to put on one data bus the following devices:
Table 4: Device Loading Example
Manufacturer
Distech Controls' devices
(⅛-load devices)
Distech Controls' BACnet
MS/TP Thermostats
(½-load devices)
Manufacturer Y
(full load devices)
Total Full-Load Devices
1. This is limited by the maximum number of master devices allowed on a BACnet MS/TP Data
Bus.
The solution for the above example is to create two data bus segments connected together by
a repeater and then split up the devices between the data bus segments, ensuring again that
the maximum number of devices on each separate data bus is not exceeded. See
Repeaters to Extend the Data Bus
Network Guide
BACnet MS/TP Communication Data Bus Fundamentals
Device load on the attached BACnet MS/TP Data
Bus
⅛-load devices
½-load devices
Refer to their documentation
Quantity of Equivalent
devices full-load
(example) devices
8 1
14 7
26 26
34
on page 28.
Maximum devices supported by
the manufacturer
1
128
Maximum 50 recommended
64
Maximum 50 recommended
32
There are too many devices on the
data bus. It is limited to a maximum
of 32 devices by Manufacturer's Y
devices.
Using
15