Supply Power Spade Terminals
Wire the 24 VAC supply power wires from the transformer
to the HOT and COM terminals on the spade terminal as
shown in
Figure 7
. See
Table 6
for more information.
Figure 7: 24 VAC Supply Power Spade Terminal
Wiring
Important:
The supply power terminal block on the
VMA18 is a two-position spade lug (
Figure
7
). Exercise caution while rewiring the
power plug when replacing an existing
controller. Stray wire strands may make
contact and cause a short circuit across the
24 VAC power supply.
To maintain proper phasing when replacing
the existing VMA14xx controller with the
VMA18 controller, connect the power wire
from 24 VAC: 1 terminal on the existing
controller to the HOT power terminal on the
VMA18. Also connect the power wire from
the 24 VAC: 2 terminal on the existing
controller to the COM power terminal on the
VMA18 controller.
The supply power wire colors may be different on
transformers from other manufacturers. Refer to the
transformer manufacturer’s instructions and the project
installation drawings for wiring details.
Important:
Connect 24 VAC supply power to the VMA
and all other network devices so that
transformer phasing is uniform across the
network devices. Powering network devices
with uniform 24 VAC supply power phasing
reduces noise, interference, and ground
loop problems. The VMA does not require
an earth ground connection. However, when
grounding the secondary of the 24 VAC
transformer is required, only one connection
to ground should be made near the
transformer.
Figure 8: Transformer Grounding
Improper wiring of this terminal may cause a short circuit
across the 24 VAC power supply on -1 models.
To wire the VMA18 Series controller, complete the
following steps:
1. Terminate wiring per engineering drawings.
2. Wire network sensors and other devices to the VMA's
Sensor/Actuator (SA) Bus.
3. Wire the N2/FC Bus in a daisy chain (see
Table 6
).
4. Ensure that the VMA’s device address DIP switches
are set to the appropriate device address. (See
Setting the Device Address
.)
5. Connect the VMA controller to 24 VAC, Class 2
power.
Refer to the
N2 VMA Application Note (LIT-12011829)
for more information about replacing an existing controller
with an VMA18 controller.
VMA Terminal Functions, Ratings,
Requirements, and Wiring Guidelines
Input and Output Wiring Guidelines
Table 4
provides information about the functions, ratings,
and requirements for the VMA input and output terminals,
and
Table 5
provides guidelines for wire sizes and cable
lengths.
In addition to the wiring guidelines in
Table 4
, observe
these guidelines when wiring VMA inputs and outputs:
•
Run all low-voltage wiring and cables separate from
high-voltage wiring.
•
All input and output cables, regardless of wire size or
number of wires, should consist of twisted, insulated,
and stranded copper wires.
•
Shielded cable is not required for input or output
cables.
7
VMA1826/1832 VAV Controller Installation Instructions
