Maximum cable length versus load
current
Use Figure 7 to estimate the maximum cable length
relative to the wire size and the load current (in mA)
when wiring inputs and outputs.
Figure 7: Maximum Wire Length by Current and
Wire Size
Communications bus and supply
power wiring guidelines
provides information about terminal block
functions, ratings, and requirements..
In addition, observe these guidelines when wiring
the SA Buses and supply power:
• Run
all
low-voltage wiring and cables separate
from high-voltage wiring.
• All SA Bus cables, regardless of wire size, should
be twisted, insulated, stranded copper wire.
• Shielded cable is strongly recommended for all SA
Bus cables.
• Refer to the
MS/TP Communications Bus
Technical Bulletin (LIT-12011034)
for detailed
information regarding wire size and cable length
requirements for SA Buses.
Communication bus and supply power terminal blocks, ratings, and requirements
Table 5: Communication bus and supply power terminal blocks, functions, ratings, requirements, and
cables
Terminal block/Port label
Terminal labels
Function, electrical ratings/
Requirements
Recommended cable type
+
-
SA Bus Communications
COM
SA Bus Signal Reference and 15 VDC
Common
SA BUS
2
POWER
15 VDC Supply Power for Devices on the
SA Bus
0.6 mm (22 AWG) stranded, 4-wire
(2 twisted-pairs), shielded cable
recommended
Note:
The + and - wires are one
twisted pair, and the COM and
SA PWR wires are the second
twisted pair.
SENSOR
SENSOR
RJ-12 6-Position Modular Port provides
SA Bus Communications
SA Bus provides 15 VDC Power for:
NS Series Sensors
MAP Gateway 4.2 or above
Bluetooth Commissioning Converter
(BTCVT)
DIS1710 Local Controller Display
VAV Balancing Tool
24 AWG 3-pair CAT 3 Cable <30.5 m
(100 ft)
ETH1 and ETH2
ETH1 and ETH2
Connect to BACnet/IP Network
Ethernet ports; 10/100 Mbps; 8-pin
RJ-45 connector
HOT
24 VAC Power Supply - Hot
Supplies 20–30 VAC (Nominal 24 VAC)
24~
COM
24 VAC Power Supply Common
The terminal is isolated from the FC bus
common.
0.8 mm to 1.0 mm
(20 to 18 AWG) 2-wire
1
To determine wire size and cable lengths for cables other than the recommended cables, see Table 4.
2
The SA bus wiring recommendations are for MS/TP Bus communications at 38.4k baud. For more information, refer to the
MS/TP
Communications BusTechnical Bulletin (LIT-12011034)
.
3
The MAP Gateway serves as a replacement for the BTCVT, which is no longer available for purchase, but continues to be supported.
VMA1930 VAV Controller Installation Guide
11