Cabling And Wiring Considerations; Air Circulation And Cooling; Compass Safe Distance - Garmin GPS 400W, GNC 420W Installation Manual

2.6

Cabling and Wiring Considerations

Wiring should be installed in accordance with AC 43.13-1B Chapter 11. For dual 400W Series unit
installations, care should be taken to ensure separation between wires of redundant systems to reduce the
possibility of loss of navigation due to a single event. When wire separation cannot be achieved, the
following issues should be addressed:
•
It should not be possible for a cable harness to be exposed to wire chafing in a manner that both
GPS units fail simultaneously;
•
The cable harness should not be located near flight control cables and controls, high electrical
capacity lines or fuel lines;
•
The cable harness should be located in a protected area of the aircraft (e.g., isolated from engine
rotor burst); and
•
Do not route cable near high-energy sources.
Wiring which is required to be shielded per Appendix H must be shielded. Pigtail lengths must
be less than 3.0 inches.
Refer to Section 3.7 and Section 3.8 for connector and tooling information.
Refer to Section 3.10 for recommended coax cable.
Refer to Appendix H for the appropriate wiring connections to assemble the wiring connector.
Once the cable assemblies have been made, attach the cable connectors to the rear connector plate. After
installing the mounting tube, attach the assembled connector plate. Route the wiring bundle as
appropriate. Use 22 to 24 AWG wire for all connections except for power. Use 20 AWG for power and
ground. Avoid sharp bends.
2.7

Air Circulation and Cooling

The 400W Series units meet all TSO requirements without external cooling. However, as with all
electronic equipment, lower operating temperatures extend equipment life. On the average, reducing the
operating temperature by 15° to 20°C (27° to 36°F) doubles the mean time between failure (MTBF).
Recommended airflow rating is 1 CFM (cubic foot per minute) at a pressure equivalent to 0.1 inches of
water.
Potential damage to your 400W Series unit may occur by using outside forced air to cool the equipment.
Therefore, it is recommended that an electric forced air fan be installed, of the indicated rating, to cool
this equipment.
Units tightly packed in the avionics stack heat each other through radiation, convection, and sometimes
by direct conduction. Even a single unit operates at a much higher temperature in still air than in moving
air. Fans or some other means of moving the air around electronic equipment are usually a worthwhile
investment. A 5/8 inch diameter air fitting is provided on the rear of the mounting rack for the purpose
of admitting cooling air under such conditions. If a form of forced air cooling is installed, make certain
that rainwater cannot enter and be sprayed on the equipment.
2.8

Compass Safe Distance

After reconfiguring the avionics in the cockpit panel, if the 400W Series unit is mounted less than 12
inches from the compass, recalibrate the compass and make the necessary changes for noting correction
data.
400W Series Installation Manual
190-00356-02
NOTE
Page 2-11
Rev. E