What is Floating Neutral? Effects and How to Test and Fix it?

Floating neutral happens when the neutral wire of a circuit disconnects from the ground. In an AC system, engineers always ground the neutral wire permanently to the earth. However, floating neutral may occur in a power system due to loose connection, braking of neutral flat, wrong circuit connection, or due to short circuit.

What is Neutral and why it is grounded?

In a three-phase AC system, each phase has a 120-degree phase difference. In a Delta-Star Transformer, the center or common point provides the same potential difference for all three windings—R, Y, and B phases—with a 120-degree phase shift.

During a balanced condition, the voltage at the neutral point stays at zero. When the load becomes unbalanced or a fault occurs, the phase angle of one phase shifts, which creates unbalanced voltage or current in the neutral wire.

To protect the system, the neutral wire of every start winding transformer is permanently grounded. If any unbalance or phase to ground occurred at the load end, the unbalance or fault current will flow to the neutral wire due to a close-loop by using the ground. By sensing the neutral current, the protection relay operates and isolates the load.

Effects of Floating Neutral:

Floating neutral is very dangerous in an AC system. Following disturbances may observe

• Unbalance voltage can develop at a neutral point and it will affect the stability of the system and connected equipment
• Due to floating ground unbalance or faulty current may not detect by the relay and the connected protection system will not operate.

How to Test for a Floating Neutral?

We know the neutral always connects to the ground, and under normal conditions, the voltage at the neutral point with respect to the ground stays at zero. If a floating neutral condition appears, some unbalanced voltage should be present at the neutral point with respect to the ground. By checking voltage between neutral and ground, it can test in the system.

How to fix floating Neutral?

Floating neutral is very unsafe for the system. Floating neutral can be attended by the grounding of the neutral wire of the system.