Engineering Documentation

Table Of Contents
Chapter 2 Network Electrical Systems
Power Trunk Guidelines
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By similar calculations, power drawn through the remaining legs is:
Trunk B Trunk C
Leg 1 = 66.7 VA Leg 1 = 42.6 VA
Leg 2 = 19.4 VA Leg 2 = 33.6 VA
Leg 3 = 47.3 VA Leg 3 = 27.9 VA
Leg 4 = 27.9 VA
Determine the voltage drop for each leg:
Voltage drop = (total VA)/24V × 0.005 ohms/ft × distance in feet
Where:
0.005 is the resistance in ohms/ft. for a pair of No. 14 AWG wires.
Trunk A
Vdrop (Leg 1) = (74.75 VA / 24V) × 0.005 ohms/ft × 10 ft. = 0.16V
Vdrop (Leg 2) = (42.2 VA / 24V) × 0.005 ohms/ft × 15 ft. = 0.13V
Vdrop (Leg 3) = (13.6 VA / 24V) × 0.005 ohms/ft × 40 ft. = 0.11V
Vdrop (Leg 4) = (28.6 VA / 24V) × 0.005 ohms/ft × 10 ft. = 0.06V
Vdrop (Leg 5) = (15 VA / 24V) × 0.005 ohms/ft × 50 ft. = 0.16V
By similar calculations, the voltage drops for the remaining legs are:
Trunk B Trunk C
Vdrop (Leg 1) = 0.18 V Vdrop (Leg 1) = 0.28V
Vdrop (Leg 2) = 0.06V Vdrop (Leg 2) = 0.28V
Vdrop (Leg 3) = 0.64V Vdrop (Leg 3) = 0.15V
Vdrop (Leg 4) = 0.15V
Determine the voltage available at the last remote actuator (A1) on controller (C1):
a. Calculate the starting voltage:
Starting voltage = 24V × 0.9 = 21.6V
Where:
0.9 is an efficiency factor.
b. Calculate the voltage drop to the last controllers or remote actuators:
Vdrop (to C1) = Vdrop (Leg 5) + Vdrop (Leg 4) + Vdrop (Leg 2) +
Vdrop (Leg 1)
= 0.16V + 0.06V + 0.13V + 0.16V
= 0.51V
c.
Calculate the voltage at the last controller remote actuator
V(A1) = Starting voltage Vdrop (to A1)
= 21.6V 0.51V
= 21.09V
d.
Check that your calculation is greater than the minimum required voltage
The minimum voltage for a DXR2 Automation Station: 20.4V
Since 21.09V is greater than the 20.4V required this leg is correct.
If these calculations had resulted in a voltage less than the minimum required, it would
have been necessary to reconfigure the layout of the power trunk.