Floating Neutral- Effect and How to Test & Fix it

A floating neutral condition happens when the neutral is not properly connected to the ground. The floating neutral can cause a risk of fire and electric shock.

Electrical power is transmitted to our home and to the industrial facilities through three phases. Each phase has a voltage of 230 V at 50Hz with respect to the neutral. The neutral point carries the reference voltage with respect to which the voltage of each phase can be measured. For a single-phase supply, One of the three phases acts as the forward path of the circuit while the return path is connected to the neutral which carries the reference voltage.

The reference voltage for a three-phase system should be zero and hence the neutral point of the three-phase system is grounded. However, if there is any problem with the grounded neutral where it doesn’t remain grounded or the ground connection breaks due to rust or due to any other mechanical failure, the neutral voltage doesn’t remain zero and holds some random or floating voltage. Such a condition is termed Floating Neutral.

representation of floating neutral

The above-given image shows a representation of a floating neutral single-phase system where the neutral has been disconnected from the ground and is now bearing a floating voltage.

Importance of Neutral grounding

In a three-phase AC system, we know that each phase is separated by a phase difference of 120 degrees (elec.) from another phase. In the case of power distribution from the distribution station, the power is distributed using a Delta-star transformer. The star configuration provides a common center point which acts as the neutral point. Voltage in each phase when measured with reference to this common center point is the same in magnitude and displaced by 120 degrees from each other.

star configuration of transformer

The importance of this neutral point is that a single-phase power supply can be done to a residence or any other facility as required by supplying power through any one phase and using the neutral point as the return path.

The neutral point is also important in case of handling a large or unbalanced load on the line. At a balanced condition, the current flowing through the neutral is zero. But in case of an unbalanced load or a fault condition that causes a phase shift, the neutral point carries the unbalanced current.

To protect the entire system as well as the operator and the consumer, the neutral point of the star-connected secondary of the transformer is grounded so that any fault or unbalanced current quickly passes into the ground without any harm. This is why the grounding of the neutral point is important. Moreover, if there is a substantial amount of neutral current, the protective relay senses it and operates the circuit breaker to avoid the spread of the fault.

If this neutral point is ungrounded due to any reason, the problem of floating neutral arises.

Effects of Floating Neutral

  • Floating neutral causes the unbalanced current or voltage to circulate in the system and this can impact the stability of the entire power system.
  • Neutral grounding causes the unbalanced current to flow to the ground which is immediately sensed by protective relays. If the neutral remains ungrounded, the fault current can’t be sensed by the relays and thus the magnitude of the fault will keep on rising.
  • Floating neutral happens when the unbalanced current flowing through the neutral to the ground faces resistance in the path. Thus it begins to flow through the path of low resistance like casing or the covering which may result in a fire outbreak and electrical shock to the people nearby.
  • Unbalanced current may destroy sensitive electronic devices within laptops, PCs, and other appliances. One may get a nasty electrical shock while touching the electrical outlet or a switch.
  • Floating neutral causes the reference voltage to be set to a non-zero value which may result in several devices facing over-voltage. Even though the single phase to neutral voltage adds up to 230 V, there is an unbalanced voltage that remains in the system.

How to Test a Floating Neutral?

Under normal circumstances, the neutral point remains grounded and hence the neutral voltage is equal to zero. In the case of an ungrounded neutral, there will be a potential difference between the neutral point of the star connection and the ground. This potential difference is nothing but the unbalanced voltage of the system. Thus by taking a measure of the potential difference between the neutral and the ground, we can say whether there is a floating neutral or not.

How to Fix a Floating Neutral?

Once the problem of floating neutral is detected, it is important to fix it as soon as possible. Here are some steps to fix a floating neutral:

  • Contact a qualified electrician who can fix the grounding problem of the neutral and ensures that the entire system is compliant with necessary safety requirements as per the electrical codes operational in that area.
  • Regular inspection of the grounding connection from the power outlet may bring the fault to the fore and will help avoid any untoward incident.
  • Ensure that there is no corrosion in the grounding connection. Rust or corrosion increases the resistance of the low-impedance ground path which shouldn’t be the case.
  • Installation of Ground Fault Circuit Interrupters (GFCI) in places where water is present like the bathroom or kitchen helps in avoiding any accident due to floating neutral. GFCI senses an unbalanced current in the system and trips the power. An electrician may be consulted to restore the system by making the necessary repair in the neutral-to-ground connection.
  • Avoid overloading. Any load beyond the permissible capacity on the line increases the chances of floating neutral due to the flow of a huge amount of current.
  • Any cheap or workable repair must be avoided. This may serve the purpose for the time being but leaves the system open for a floating neutral problem.

In conclusion, floating neutral is a serious problem and should be treated as one. With the increase in the number of consumers and the demand for electricity, the load on the entire power system is also increasing and there is a commensurate rise in the incidents of floating neutral. Hence, the only way to avoid it is through regular inspection and compliance with safer practices in the industry.

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