A useful experimental aircraft wiring example is not a copy-and-paste electrical design. It is a planning model that shows how power moves from the battery to the starter, alternator, main bus, avionics bus, essential equipment, and individual circuit protection. The details must match the aircraft, installed equipment, engine, electrical load, wire runs, and operating mission.
For an RV, Glasair, Lancair, Kitfox, Sonex, or other amateur-built project, the objective is straightforward: build an electrical system that is protected, labeled, maintainable, and understandable on the ground and under pressure in flight. A clean panel is valuable. A clean wiring architecture is what keeps the panel functional.
Start With the Electrical Architecture
Before selecting wire, breakers, switches, or bus components, identify what the aircraft must do after engine start and what it must retain after an electrical fault. A day VFR aircraft with a basic VHF radio has different requirements than an IFR-capable cross-country aircraft with dual EFIS displays, an IFR navigator, ADS-B Out transponder, autopilot, engine monitor, audio panel, and electrically dependent engine components.
Most modern experimental panels use a battery, starter contactor, master contactor, alternator or alternators, and one or more protected distribution buses. The system may use conventional circuit breakers, automotive-style fuses, electronic circuit protection, or a combination. No one approach is automatically right. The correct choice depends on equipment requirements, available panel space, fault-isolation needs, and how easily the system can be serviced later.
A conventional split-bus arrangement remains easy to understand:
```text
Battery
|
Starter Contactor ---> Starter Motor
|
Master Contactor
|
Main Bus
|---- Lighting / pitot heat / flap motor / trim
|---- Fuel pump / landing gear / cabin equipment
|
Avionics Master or Avionics Bus
|---- GPS/NAV/COM
|---- Audio panel
|---- Transponder / ADS-B
|---- EFIS displays
|---- Autopilot
|
Essential Bus
|---- Primary flight display or standby instruments
|---- Engine monitor
|---- Primary COM or navigator
|---- Essential fuel pump, if electrically required
```
This layout is an example, not a required architecture. Many builders eliminate the traditional avionics master switch because modern equipment may have its own startup protections and manufacturers may specify direct power connections. Others use a dedicated avionics bus controlled by a relay or electronic power control system. Follow each avionics manufacturer’s installation manual, particularly for power, grounding, cooling, circuit protection, and interconnect requirements.
Define the Loads Before Sizing the Buses
The most common wiring-planning mistake is designing the panel first and calculating the electrical loads afterward. Build a load analysis before committing to bus capacity, alternator output, battery size, or backup power strategy.
List every electrical consumer, its normal current draw, peak draw, voltage range, recommended circuit protection, and whether it is needed for continued safe flight. Include equipment that is easy to overlook, such as USB charging outlets, CO detectors, heated seats, flap motors, trim servos, boost pumps, landing lights, strobes, and annunciators.
A typical glass-panel aircraft can have modest cruise electrical demand but substantial intermittent loads. Pitot heat, landing lights, flap operation, and a fuel pump can materially change the demand profile. If the airplane will be flown IFR, calculate normal cruise draw, worst-case draw, alternator-out draw, and battery endurance for the equipment you intend to keep powered.
The essential bus should support the equipment required to navigate, communicate, monitor the engine, and manage the aircraft following loss of primary generation. That does not mean every panel device belongs on the essential bus. Separating essential and nonessential loads prevents a failed accessory circuit from taking unnecessary equipment offline.
A Practical Single-Alternator Example
Consider a single-engine experimental with a 60-amp alternator, a battery, two EFIS displays, an engine monitor, IFR GPS/NAV/COM, second COM, audio panel, transponder, ADS-B, autopilot servos, electric trim, LED exterior lighting, electric fuel pump, and pitot heat.
The main bus can carry high-draw and noncritical loads such as exterior lighting, pitot heat, flap motor, trim, auxiliary power outlets, and cabin accessories. The avionics bus can support the navigator, radios, audio panel, transponder, ADS-B receiver, displays, and autopilot. The essential bus can be fed through a separately protected path and carry one display, the engine monitor, one communication/navigation source, and any electrically required fuel or ignition component.
If the primary alternator fails, the pilot can shed lights, pitot heat when conditions permit, the second display, the second radio, and other nonessential equipment. The remaining battery capacity is reserved for the equipment that supports the flight plan and safe landing. The actual endurance calculation depends on measured equipment current, battery condition, temperature, and the aircraft’s electrical configuration.
Wire Size Is About More Than Amperage
Wire gauge must be selected for current, wire length, allowable voltage drop, installation environment, and the equipment manufacturer’s instructions. A wire that is adequate for current capacity may still create unacceptable voltage drop on a long run to a sensitive avionics component or landing light.
Use aviation-grade wire appropriate for the installation, such as MIL-spec insulated aircraft wire commonly used in amateur-built aircraft. Avoid treating general-purpose automotive wire as a direct substitute. Heat resistance, abrasion resistance, flexibility, identification, and long-term reliability matter in the engine compartment and behind an instrument panel.
For avionics power feeds, keep voltage drop low and use the wire size specified by the manufacturer whenever possible. GPS navigators, EFIS systems, digital engine monitors, and transponders may be sensitive to low voltage during cranking or high-load operation. Some equipment needs a direct battery feed with dedicated protection for memory retention, backup functions, or controlled shutdown behavior.
Every wire should be supported at appropriate intervals, protected where it passes through structure, and kept clear of sharp edges, control runs, exhaust components, and high-heat areas. Grommets, conduit, adel clamps, strain relief, and proper service loops are not cosmetic details. They prevent chafing, fatigue, and connector damage over years of vibration.
Grounding and Shielding Need a Deliberate Plan
A reliable aircraft electrical system does not use the airframe as an afterthought. Establish a grounding strategy early. Many builders use a central ground block or forest-of-tabs arrangement connected by a substantial conductor to the engine or battery negative, depending on the aircraft design. This makes troubleshooting easier and reduces the temptation to create random local grounds throughout the panel.
High-current engine and starter grounds require appropriately sized conductors and sound bonding connections. Avionics grounds should follow each manufacturer’s instructions. Do not assume that a radio, EFIS, or audio panel can share a noisy power ground with motors, strobes, or high-current lighting circuits without consequences.
Audio and data wiring deserve special attention. Shielded cable is often required for microphone audio, headset audio, magnetometer wiring, serial data, antenna-related connections, and certain sensor circuits. Shield termination is application-specific. Grounding both ends when the equipment manual calls for a single-point shield termination can introduce noise or ground-loop issues.
Keep ignition leads, alternator wiring, strobe power supplies, and high-current motor wiring separated from low-level audio and data wiring where practical. Crossing at a right angle is generally preferable to routing parallel for long distances. The payoff is a quieter headset, cleaner autopilot performance, and fewer frustrating intermittent faults.
Circuit Protection Must Protect the Wire
Circuit breakers and fuses are selected primarily to protect the wire and secondarily to isolate a failed load. Size protection according to the wire gauge, expected load, inrush characteristics, and equipment manufacturer guidance. Installing an oversized breaker because a smaller one trips is not a fix. Find the cause of the current draw, voltage issue, or incorrect circuit design.
Place circuit protection as close as practical to the power source for each feeder. Large battery cables and alternator output wiring may require current limiters or fusible-link-style protection designed for high-current aircraft applications. These circuits need careful planning because a short in an unfused high-current conductor can have serious consequences.
Clearly label breakers, fuses, relays, disconnects, and buses. Labels should remain readable from the normal maintenance position, not only while standing at the workbench with the panel removed.
Build for Maintenance, Not Just First Flight
An organized harness saves time at annual condition inspection and when adding equipment later. Leave enough service length to remove a radio stack component or swing a panel section without pulling terminals tight. At the same time, avoid large unsupported wire bundles that can vibrate or obscure other systems.
Use consistent wire identification at both ends, documented connector pinouts, and a current wiring diagram. The finished airplane should include a power-distribution drawing, interconnect diagram, grounding plan, circuit-protection schedule, and equipment configuration records. If a future owner, A&P, or avionics technician cannot trace a circuit, the installation is not truly finished.
Before energizing the completed system, inspect every terminal, verify torque where specified, confirm fuse or breaker values, and test continuity for intended circuits and unintended shorts. Power the system in stages. Verify charging voltage, radio transmit performance, GPS operation, audio quality, transponder function, autopilot behavior, and failure modes before closing the panel.
For complex glass-panel, IFR, dual-battery, or electrically dependent-engine projects, Gulf Coast Avionics can help match avionics, circuit-protection hardware, and installation planning to the aircraft mission. A wiring diagram becomes much more useful when it reflects the actual equipment and operating requirements of the airplane being built.
The best time to simplify a wiring problem is before the first terminal is crimped. Start with the loads, protect each conductor, document every decision, and leave the finished aircraft ready for the next inspection, upgrade, or unexpected electrical fault.