PS Engineering
PAC45 Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-045-0100
Page 2-3
January 2020
PS Engineering recommends that Loctite #425 be added to any thumbscrew that is removed and
reinstalled. Loctite #425 is added to the thumbscrew threads at the factory.
2.4 Cable Harness Wiring
Referring to the appropriate Appendix, assemble a wiring harness as required for the installa-
tion. All wires must be MIL-SPEC in accordance with current regulations. Two- and three-con-
ductor shielded wire must be used where indicated, and be MIL-C-27500 or equivalent specifica-
tion. Proper stripping, shielding and soldering technique must be used at all times. It is
imperative that correct wire be used.
Refer to FAA Advisory Circular 43.13-2B for more information. Failure to use correct techniques
may result in improper operation, electrical noise or unit failure. Damage caused by improper
installation will void the PS Engineering warranty.
See Appendix C and D for intercom connection configurations. It is critical to the proper opera-
tion of this system to have this connector wiring made in accordance with these diagrams. Use
2- and 3-conductor, MIL-spec cable as shown. Connect the shields at the audio controller end
only, and tie to the audio low inputs as shown.
2.4.1 Electrical Noise
Due to the variety and the high power of radio, equipment often found in today's aircraft, there
is a potential for both radiated and conducted noise interference.
The PAC45D power supply is specifically designed to reduce conducted electrical noise on the
aircraft power bus by at least 50dB. Although this is a large amount of attenuation, it may not
eliminate all noise, particularly if the amplitude of noise is very high. Shielding can reduce or
prevent radiated noise (i.e., beacon, electric gyros, switching power supplies, etc.) However, in-
stallation combinations can occur where interference is possible. The PAC45D was designed in
an RFI hardened chassis and has internal Electromagnetic Interference (EMI) filters on all inputs
and outputs.
Ground loop noise occurs when there are two or more ground paths for the same signal (i.e.,
airframe and ground return wire). Large cyclic loads such as strobes, inverters, etc., can inject
noise signals onto the airframe that are detected by the audio system. Follow the wiring dia-
gram very carefully to help ensure a minimum of ground loop potential. Use only Mil Spec
shielded wires (MIL-C-275000, or better). Under no circumstances combine a microphone and
headphone wiring into the same shielded bundle. Always use a 2- or 3-conductor, shield wire as
shown on the installation-wiring diagram.
The shields can be daisy-chained together, and then connected to the ground.
Radiated signals can be a factor when low-level microphone signals are "bundled" with current
carrying power wires. Keep these cables physically separated. It is very important that you use
PRELIMINARY
