Distech Controls ECB-VAV, User Manual

Page: 47 / 138

BACnet MS/TP Communication Data Bus Fundamentals
Network Guide 45
For non-VAV devices, determine the appropriate size transformer for the job as follows:
1. Add up the power requirements of all devices plus all external loads (see About External
Loads on page 42). Multiply the total power needed by a multiplier of 1.3, as a security
margin. For example, to power five devices (15 VA each), the total load is 75 VA multiplied
by 1.3 is 98 VA. Choose a size of transformer just over this amount: For example, a 100
VA model.
2. When the total load of a number of devices requires a transformer with a rating greater
than 100 VA, use two or more transformers. Ensure that the load to be connected to each
transformer follows the guideline of Step 1 above.
Recommended 24V Power Cable
The table below lists Distech Controls' recommended power cable.
24VAC Power Supply Connection
Use an external fuse on the 24VAC side (secondary side) of the transformer, as shown in Fig-
ure 28 , to protect all controllers against power line spikes.
Laboratory testing conditions for the above graph are as follows:
• Distance between each VAV is evenly spaced along the entire wire length
• Transformer specification: 100VA (120/24VAC)
• Tested at room temperature with low voltage line conditions: 108VAC (50Hz)
Always use a separate transformer for each ECL-600 series controller and for each
of its associated I/O Extension Modules. See
ECx-4XX I/O Extension Module
Power Supply Requirements on page 47.
Table 10: Distech Controls Recommended 24V Power Cable
Cable Type
AWG -
Number of
Conductors Non-Plenum Applications (FT4) Plenum Applications (FT6)
Part Number O.D. (Ø) Part Number O.D. (Ø)
18-2 CB-W181P-
1002 5.0mm / 0.20in. CB-W181P-
2051 5.0mm / 0.20in.
16-2 CB-W161P-
1031 4.8mm / 0.19in. CB-W161P-
2062 4.8mm / 0.19in.
14-2 CB-W141P-
1081 7.2mm / 0.29in. CB-W141P-
2013 7.2mm / 0.29in.