Page 12
VP-X Installation and Operating Manual
Rev. D (August 5, 2020)
When you know the current draw for each device, use the chart below to
size the power wires. For simplicity, the VP-X wiring harnesses (purchased
separately) use the four wire sizes in the table.
Up to (amps)
Use wire size (AWG)
5A
20
10A
18
15A
14
Data signal
22
3.5 Grounding
Many people think that the power, or positive, wire is the most important wire
to provide electricity to a device. The electrical ground is just as important as
electricity must flow the entire path from the power source to the device and
back to the source. The ground wire must be the same wire gauge or a larger
diameter (smaller gauge number) as the wire that provides power to the
device, with the exception of VP-X ground wires from J12-4 and J10-9. See
section 5.17 for more information..
A
ground loop
is when electricity takes two different paths, and each path
has a different resistance. Ground loops are most noticeable in aircraft audio
equipment, and can produce a variety of problems, most notably unwanted
noise.
Grounding is as much of an art as it is a science. With that in mind, several
options for grounding your system are provided below. Choose the one that
best fits your needs. Keep in mind that more wiring means more weight
(although likely negligible). Also, note that in all the examples below the
avionics grounds are kept together.
• Option 1: Run a ground wire from each and every electrical device
back to a common grounding point, typically a ground bus on the
firewall.
• Option 2: Run ground wires from all the avionics to an intermediate
grounding point, then run a larger wire from the local ground bus
to the firewall ground. Run wires from all the other devices to the
firewall ground.
•
Option 3: Run the ground wires from the avionics to the firewall
ground, and run the other ground wires to a local ground (a metal
part of the airframe located near the device).
3.6
Switch Nomenclature
The chart below shows the most common switch types. A parenthesis ( )
around a switch position indicates it is a momentary, spring-loaded position.
Switch Type
Design
Symbol
Mechanism
Single Pole,
Single Throw
SPST
OFF-ON
OFF-(ON)
OFF-(ON)
Single Pole,
Double Throw
SPDT
ON-NONE-ON
ON-OFF-ON
(ON)-OFF-(ON)
ON-OFF-(ON)
Double Pole,
Single Throw
DPST
OFF-ON
OFF-(ON)
Double Pole,
Double Throw
DPDT
ON-NONE-ON
ON-OFF-ON
(ON)-OFF-(ON)
ON-OFF-(ON)
