Define an open circuit, short to ground, and short to power with practical examples in avionics wiring.

Define an open circuit, short to ground, and short to power with practical examples in avionics wiring.

• A. Open circuit occurs when a fuse blows.
• B. Open circuit occurs when a conductor is broken, preventing any current flow.
• C. Short to ground occurs when a device touches the airframe ground.
• D. Short to power occurs when a device contacts the positive supply.

Answer: (B)

An open circuit means the path for current is incomplete, so no current can flow. In avionics wiring, this happens when a conductor is broken or a switch or connector is open, leaving the circuit open. For example, if a sensor lead in a cockpit instrument wiring harness is physically fractured, the circuit to that sensor can’t be completed—there’s no return path, so the sensor won’t energize or report data even though the power supply is present. A short to ground occurs when a live conductor touches the aircraft structure or another grounded path, creating a low-resistance path directly to ground. This draws a large amount of current, which protection devices like fuses or circuit breakers respond to by opening the circuit. An example is a chafed wire that rubs against the airframe and makes contact with the airframe ground, causing a ground fault. A short to power is when a conductor makes contact with the positive supply, creating a direct fault path from the supply into the circuit. This also drives a high current, often resulting in blown fuses or tripped breakers and potential overheating. An example would be insulation damage that allows a wire to touch the positive 28-volt bus, energizing unintended components or wiring. So, the statement that an open circuit is caused by a broken conductor best captures the definition: the circuit is not complete, preventing current from flowing. The other scenarios describe fault conditions that create unexpected current paths rather than simply having an incomplete path.

An open circuit means the path for current is incomplete, so no current can flow. In avionics wiring, this happens when a conductor is broken or a switch or connector is open, leaving the circuit open. For example, if a sensor lead in a cockpit instrument wiring harness is physically fractured, the circuit to that sensor can’t be completed—there’s no return path, so the sensor won’t energize or report data even though the power supply is present.

A short to ground occurs when a live conductor touches the aircraft structure or another grounded path, creating a low-resistance path directly to ground. This draws a large amount of current, which protection devices like fuses or circuit breakers respond to by opening the circuit. An example is a chafed wire that rubs against the airframe and makes contact with the airframe ground, causing a ground fault.

A short to power is when a conductor makes contact with the positive supply, creating a direct fault path from the supply into the circuit. This also drives a high current, often resulting in blown fuses or tripped breakers and potential overheating. An example would be insulation damage that allows a wire to touch the positive 28-volt bus, energizing unintended components or wiring.

So, the statement that an open circuit is caused by a broken conductor best captures the definition: the circuit is not complete, preventing current from flowing. The other scenarios describe fault conditions that create unexpected current paths rather than simply having an incomplete path.