Crestron Cresnet Network - Example Scenarios

22 • Cresnet® Network Design Guide — Doc. 9292A
The R (resistance)value correlates with a wire gauge as shown in the following table. Therefore,
using the equation above, the selected wire gauge must correlate with a resistance value that is
less than the value derived from 40,000 / (L x PF).
Resistance Value to Wire Gauge Comparison Table
Resistance (R)Value Wire Gauge
1.6 Ω 12AWG (3.31mm
2
) - Cresnet High-Power
6 Ω 18AWG (0.82mm
2
) - Cresnet Standard Power
Example Scenarios
The following example scenarios show how the resistance equation can be used to solve for
different variables within a Cresnet wiring run.
Example Scenario #1:Calculate Wire Gauge
This scenario explains how to calculate the wire gauge needed for powering one GLS-ODT-C-CN
occupancy sensor (requiring 1.5W)that is 1,500ft (457mm)away from its power source.
Use the resistance formula to calculate the resistance value of the wire run, where 1,500 is the
value for L (length of wiring run) and 1.5 is the value for PF (Cresnet power factor):
l
R < 40,000/(1,500x1.5)
l
R< 17.8
Next, use the table above to compare the resistance value of the wiring run with the resistance
value of the Cresnet wires.For this scenario, any wire gauge with a resistance value less than
17.8 can be used to supply power to the GLS-ODT-C-CN.
Example Scenario #2:Calculate Wire Run Length
This scenario explains how to calculate the maximum distance that twelve SSC-102-EL room
occupancy hallway signs (requiring 2.4Weach for a total of 28.8W) can be placed from a client
control system using 12 AWG(3.31mm
2
)wire.
Rewrite the resistance formula to solve for L, where 1.6 is the value for R (resistance value
correlating with the wire AWG) and 28.8 is the value for PF (Cresnet power factor):
l
L < 40,000/(1.6x28.8)
l
L<868
For this scenario, the maximum length of wiring that can be run to the SCC-102-ELdevices from
the power source is 868ft (265m).
NOTE:if using standard power Cresnet wire (18 AWG), the maximum length of wiring would
be 231ft (70m) , as derived from L< 40,000 / (6 x 28.8).