GROUNDED SYSTEMS

The term grounded system means that one leg of the system connects to a common conductor. This common conductor can be the Earth, the skin of the aircraft, or a structural member of the aircraft. When the grounded leg of the circuit connects to a good electrical conductor, this conductor may serve as one leg of the circuit, cutting out the need for a separate conductor.

Although the grounds are at different points, the potential at these points is the same since they connect to a common conductor.

The letter N designates any wire that completes the equipment circuit to the ground network. Any wire designated as N may come in contact with ground at any point without causing the equipment to malfunction. Grounding three-wire systems can be done by grounding one of the phases, usually the B-phase in aircraft. In four-wire systems, the neutral is ground.

The grounded circuit is better than the ungrounded one because it reduces overall weight by using fewer conductors. This results in a reduction in cost and space requirements. Other advantages are that troubleshooting is simplified and the impedance of the ground return path is lower than that of a run conductor.

A disadvantage of a grounded system is that short circuits result when a bare spot on any ungrounded conductor touches ground. Another disadvantage is having circuits of different potentials and frequencies use a common ground. There is a possibility of one circuit feeding into another. This problem often happens in electronic circuits.

Ungrounded Systems. The term ungrounded system means that the circuit in no way connects to ground. All conductors run from the power source to the loads. Circuits of this type are often referred to as being above ground. The ungrounded system has one advantage—it prevents one circuit from feeding into another because the circuits are completely insulated from each other. The system has the disadvantage of adding more weight because it requires more conductors than the grounded system.This results in added cost and space requirements. Both the grounded and ungrounded systems are used for specific purposes in modern aircraft. Single-phase and Polyphase Systems.

Single-phase systems are of simple design and construction.

They are used when there are relatively low power requirements. Polyphase systems are more complicated in construction and design. These systems are used when high power is required. These systems provide a smoother source of power. Single-phase power is available from polyphase systems. When doing this, the load on the polyphase system must be kept balanced.

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