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.
• Shielded is recommended for input and output
cables that are exposed to high electromagnetic
or radio frequency noise.
• Cable runs of less than 30 m (100 ft) typically do
not require an offset in the input/output software
setup. Cable runs over 30 m (100 ft) may require
an offset in the input/output software setup.
Maximum cable length versus load
current
Use Figure 13 to estimate the maximum cable
length relative to the wire size and the load current
(in mA) when wiring inputs and outputs.
N2/FC and SA bus and supply power
wiring guidelines
Table 6 provides information about terminal block
functions, ratings, and requirements.
Table 6 also provides wire size, cable type, and
cable length guidelines for wiring the VMA
communication buses and supply power.
In addition to the guidelines in Table 6, observe
these guidelines when wiring the SA and N2/FC
Buses and supply power:
• Run all low-voltage wiring and cables separate
from high-voltage wiring.
• All N2/FC and SA Bus cables, regardless of wire
size, should be twisted, insulated, stranded
copper wire.
• Shielded cable is strongly recommended for all
N2/FC and SA Bus cables.
• Refer to the
N2 Communications Bus Technical
Bulletin (LIT-636018)
for detailed information
regarding wire size and cable length
requirements for the N2/FC and SA buses.
Termination diagrams
A set of Johnson Controls
®
termination diagrams
provides details for wiring inputs and outputs to
the VMA18 Series controllers. See the figures in this
section for the applicable termination diagrams.
Table 2: Termination details
Type of field device
Type of Input/
Output
Termination diagrams
Voltage Input -
External Source
UI
VMA1826/1832 VAV Controller Installation Guide
8