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P
RODUCT
O
VERVIEW
N
ETWORKING
C
ONSIDERATIONS
MATRIX BACnet Router User Manual (6/6/2007)
1-7
1.3 N
ETWORKING
C
ONSIDERATIONS
As the MATRIX BACnet router is compliant to the standards of ASHRAE/ANSI 135, there are
considerations that must be kept in mind when designing a BACnet inter-network using this product.
Following these simple guidelines will ensure project success.
1.3.1 MS/TP M
EDIUM
R
ULES
Specified by ASHRAE, an MS/TP network shall use shielded, twisted-pair cable with characteristic
impedance between 100 and 130 ohms. The maximum length of an MS/TP network is 4000 feet (1200
meters) using 18 AWG cabling. An MS/TP network shall have no “T” or “star” based network connections.
Networks requiring a longer distance may utilize an optically isolated repeater to extend this limit.
1.3.2 MS/TP N
ETWORK
L
OADING
The MATRIX BACnet Router, as well as American Auto-Matrix Native Series unitary controllers, use half-
watt serial driver technology. By law of electrical limitations, a serial network of half-watt devices may
consist of up to 64 devices total.
The MATRIX BACnet Router has been qualified to accept a network of up to 63 additional BACnet MS/TP
devices ( 63 devices = 64 load limit). This qualification process included verifying electrical network
capacitance provisions, as well as optimal bandwidth speed.
While it may be possible to achieve more than the above mentioned limit using media converters and
repeaters, American Auto-Matrix discourages applications that exceed this limit. If you need to network
more devices as part of an MS/TP network, it is recommended that you purchase additional MATRIX
BACnet Router hardware.