Distech Controls ECL/ECB-PTU Series User Manual

46 Network Guide
Maintain consistent polarity when connecting controllers and devices to the transformer, as
shown in Typical Device BACnet MS/TP LAN and Power Wiring Diagram on page 49. That is,
the 24V COM terminal of each controller and each peripheral must be connected to the same
terminal on the secondary side of the transformer. This transformer terminal must be con-
nected to the building's ground. This ensures that the reference terminals of all devices con-
nected to any BACnet MS/TP data bus in the building are at the same potential.
Most Distech Controls devices use the 24V COM terminal as the signal reference point for the
data bus (see Table 1 and Figure 3) for common device terminal labels). As a consequence,
you must wire the power supply (for any given number of devices) as shown in Figure 28, such
that the transformer's secondary that is connected to 24V COM / C terminals is connected to
the building's ground at the power supply
. This ensures that the 24V COM /C terminals of all
devices connected to any BACnet MS/TP data bus in the building are at the same electrical
potential.
Figure 28: Power Wiring diagram
As specified by electrical safety codes worldwide, the building's protective ground
network must not be used to conduct electrical current under normal conditions.
Such current can lift the reference voltage sensed at a controller's 24V COM termi-
nal, thus resulting in data transmission errors.
A mechanical ground is unacceptable: Do not use a pipe, conduit, or duct work for
a ground. The power supply must have a dedicated ground wire that comes from
the main electrical supply panel.
Any connection between buildings cannot be made with BACnet MS/TP. For inter-
building connections, it is recommended to use a BACnet/IP or FOX network con-
nection. See Inter-Building BACnet Connection on page 39.
24 VAC
AC Power
Source
24 / 120 / 208 /
240 / 277 / 347 /
480 VAC, 1Ø, 2-
Wire plus Ground
24V COM
24V AC/DC
BACnet Device
Power Supply
Fuse: 4A Max.
Fast Acting
C
RC
BACnet Thermostat
24 VAC/COM
to Ground –
At
Transformer
Only
Maintain consistent
polarity when connecting
controllers and devices to
the transformer.
The 24V COM / C
terminals of all devices
must be connected to the
power supply bus that is
grounded.
24V COM
24V AC/DC
BACnet Device
GND
24V COM
24V AC/DC
BACnet Device
GND
Ground
connection is
isolated from
24V COM

Distech Controls ECL/ECB-PTU Series Specifications

General

Brand	Distech Controls
Model	ECL/ECB-PTU Series
Category	Controller
Language	English