junction

Any other steps you can offer fome to have donas faamorgroundinstalledsomething my electrician FPL cld do at wld protect e

on Pro Premium membership and video courses bundles with discount code

If theNeutral Conductoris opened, broke or lost at either of its source side (Distribution Transformer, Generator or at Load side Distribution Panel of Consumer), the distribution systems neutral conductor will float or lose its reference ground Point.

The floating neutral condition can cause voltages to float to a maximum of its Phase volts RMS relative to ground, subjecting to its unbalancing load Condition. Floating Neutral conditions in the power network have different impact depending on the type of Supply, type of installation and Load balancing in the Distribution.

Broken NeutralorLoose Neutralwould damage to the connected load or create hazardousTouch Voltageat equipment body.

AnyotherstepsyoucanofferformetohavedoneasfarasmoregroundsinstalledorsomethingmyelectricianorFPLcoulddothatwouldprotectthehomeifthatwouldhappenagainformFPL

If the Star Point of Unbalanced Load is not joined to the Star Point of its  Power Source (Distribution Transformeror Generator) then Phase voltage do not remain same across each phase but its vary according to the Unbalanced of the load.

As the Potential of such an isolated Star Point or Neutral Point is always changing and not fixed so its calledFloating Neutral.

Normal Power Condition and Floating Neutral ConditionNormal Power Condition

AnyotherstepsyoucanofferformetohavedoneasfarasmoregroundsinstalledorsomethingmyelectricianorFPLcoulddothatwouldprotectthehomeifthatwouldhappenagainformFPL

On 3-phase systems there is a tendency for the star-point and Phases to want to balance out based on the ratio of leakage on each Phase to Earth. The star-point will remain close to 0V depending on the distribution of the load and subsequent leakage (higher load on a phase usually means higher leakage).

Three phase systems may or may not have aneutral wire. A neutral wire allows the three phase system to use a higher voltage while still supporting lower voltage single phase appliances. In high voltage distribution situations it is common not to have a neutral wire as the loads can simply be connected between phases (phase-phase connection).

AnyotherstepsyoucanofferformetohavedoneasfarasmoregroundsinstalledorsomethingmyelectricianorFPLcoulddothatwouldprotectthehomeifthatwouldhappenagainformFPL

Three phases has properties that make itvery desirablein electric power systems.

Firstly the phase currents tend to cancel one another (summing to zero in the case of a linear balanced load). This makes it possible to eliminate the neutral conductor on some lines. Secondly power transfer into a linear balanced load is constant.

Most domestic loads are single phase. Generally three phase power either does not enter domestic houses or it is split out at the main distribution board.

Kirchhoffs Current Lawstates that the signed sum of the currents entering a node iszero. If the neutral point is the node, then, in a balanced system, one phase matches the other two phases, resulting in no current through neutral. Any imbalance of Load will result in a current flow on neutral, so that the sum of zero is maintained.

For instance, in a balanced system, current entering the neutral node from one Phase side is considered positive, and the current entering (actually leaving) the neutral node from the other side is considered negative.

This gets more complicated in three phase power, because now we have to consider phase angle, but the concept is exactly the same. If we are connected in Star connection with a neutral, then the neutral conductor will have zero current on it only if the three phases have the same current on each. If we do vector analysis on this, adding upsin(x),sin(x+120), andsin(x+240), we getzero.

The same thing happens when we are delta connected, without a neutral, but then the imbalance occurs out in the distribution system, beyond the service transformers, because the distribution system is generally a Star Connected.

The neutral should never be connected to a ground except at the point at the service where the neutral is initially grounded (At Distribution Transformer). This can set up the ground as a path for current to travel back to the service. Any break in the ground path would then expose a voltage potential.

Grounding the neutral in a 3 phase system helps stabilize phase voltages. A non-grounded neutral is sometimes referred to as a floating neutral and has a few limited applications.

Power flows in and out of customers premises from the distribution network, entering via the Phase and leaving via the neutral. If there is a break in the neutral return path electricity may then travel by a different path. Power flow entering in one Phase returns through remaining two phases. Neutral Point is not at ground Level but it Float up to Line Voltage.

This situation can be very dangerous and customers may suffer serious electric shocks if they touch something where electricity is present.

Broken neutrals can be difficult to detect and in some instances may not be easily identified. Sometimes broken neutrals can be indicated by flickering lights or tingling taps.

Voltage Measurement between Neutral to Ground

Arule-of-thumbused by many in the industry is that Neutral to ground voltage of 2V or less at the receptacle is okay, while a few volts or more indicates overloading; 5V is seen as the upper limit.

If Neutral to ground voltage is low at the receptacle than system is healthy, If It is high, then you still have to determine if the problem is mainly at the branch circuit level, or mainly at the panel level.

Neutral to ground voltage exists because of the IR drop of the current traveling through the neutral back to the Neutral to ground bond. If the system is correctly wired, there should be no Neutral to Ground bond except at the source transformer (at what the NEC calls the source of the Separately Derived System, or SDS, which is usually a transformer).

Under this situation, the ground conductor should have virtually no current and therefore noIR dropon it. In effect, the ground wire is available as a long test lead back to the Neutral to ground bond.

A high reading could indicate ashared branch neutral, i.e., a neutral shared between more than onebranch circuits. This shared neutral simply increases the opportunities for overloading as well as for one circuit to affect another.

A certain amount of Neutral to ground voltage is normal in a loaded circuit. If the reading is stable at close to 0V. There is a suspect an illegal Neutral to ground bond in the receptacle (often due to lose strands of the neutral touching some ground point) or at the subpanel.

Any Neutral to ground bonds other than those at the transformer source (and/or main panel) should be removed to prevent return currents flowing through the ground conductors.

Various Factors which cause Neutral Floating

There are several factors which are identifying as the cause of neutral floating. The impact of Floating Neutral is depend on the position where Neutral is broken:

Neutral failure at transformer is mostly failure of Neutral bushing.

The use of Line Tap on transformer bushing is identified as the main cause of Neutral conductor failure at transformer bushing. The Nut on Line Tap gets loose with time due to vibration and temperature difference resulting in hot connection. The conductor start melting and resulting broke off Neutral.

Poor workmanship of Installation and technical staff also one of the reasons of Neutral Failure.

A broken Neutral on Three phases Transformer will cause the voltage float up to line voltage depending upon the load balancing of the system. This type of Neutral Floating may damage the customer equipment connected to the Supply.

Under normal condition current flow from Phase to Load to Load to back to the source (Distribution Transformer). When Neutral is broken current from Red Phase will go back to Blue or Yellow phase resulting Line to Line voltage between Loads.

2) Broken Overhead Neutral conductor in LV Line

The impact of broken overhead neutral conductor at LV overhead distribution will be similar to thebroken at transformer. Supply voltage floating up to Line voltage instead of phase voltage. This type of fault condition may damage customer equipment connected to the supply.

3) Broken of Service Neutral Conductor

A broken Neutral of service conductor will only result of loss of supply at the customer point. No any damages to customer equipments.

4) High Earthing Resistance of Neutral at Distribution Transformer:

Good Earthing Resistance of Earth Pit of Neutral providelow resistance path for neutral currentto drain in earth. High Earthing Resistance may provide high resistance Path for grounding of Neutral at Distribution Transformer.

Limit earth resistance sufficiently low to permit adequate fault current for the operation of protective devices in time and to reduce neutral shifting.

5) Over Loading and Load Unbalancing

Distribution Network Overloading combined with poor load distribution is one of the most reason of Neutral failure. Neutral should be properly designed so that minimum current will be flow in to neutral conductor. Theoretically the current flow in the Neutral is supposed to be zero because of cancellation due to 120 degree phase displacement of phase current.

In Overloaded Unbalancing Network lot of current will flow in Neutral which break Neutral at its weakest point.

Some buildings are wired so that two or three phases share a single neutral.The original idea was to duplicate on the branch circuit level the four wire (three phases and a neutral) wiring of panel boards. Theoretically, only the unbalanced current will return on the neutral. This allows one neutral to do the work for three phases. This wiring shortcut quickly became a dead-end with the growth of single-phase non-linear loads. The problem is that zero sequence current

From nonlinear loads, primarily third harmonic, will add up arithmetically and return on the neutral. In addition to being a potential safety problem because of overheating of an undersized neutral, the extra neutral current creates a higher Neutral to ground voltage.

This Neutral to ground voltage subtracts from the Line to Neutral voltage available to the load. If youre starting to feel that shared neutrals are one of the worst ideas that ever got translated to copper.

Normally LV network are mostly not given attention by the Maintenance Staff.Looseorinadequate tighteningof Neutral conductor will effect on continuity of Neutral which may cause floating of Neutral.

Let us take one example to understandNeutral Floating Condition.We have a Transformer which Secondary is star connected,Phase to neutral = 240VandPhase to phase = 440V.

Condition (1) Neutral is not Floating

Whether the Neutral is grounded the voltages remain the same 240V between phase & Neutral and 440V between phases. The Neutral is not Floating.

Condition (2) Neutral is  Floating

All Appliances are connected:If the Neutral wire for a circuit becomes disconnected from the households main power supply panel while the Phase wire for the circuit still remains connected to the panel and the circuit has appliances plugged into the socket outlets. In that situation, if you put a voltage Tester with a neon lamp onto the Neutral wire it will glow just as if it was Live, because it is being fed with a very small current coming from the Phase supply via the plugged-in appliance(s) to the Neutral wire.

All Appliances are Disconnected:If you unplug all appliances, lights and whatever else may be connected to the circuit, the Neutral will no longer seem to be Live because there is no longer any path from it to the Phase supply.

This is because the neutral is floats above ground potential(110V + 120V = 230VAC). As a result the output is isolated from system ground and the full output of 230V is referenced between line and neutral with no ground connection.

If suddenly disconnect the Neutral from the transformer Neutral but kept the loading circuits as they are, Then Load side Neutral becomes Floating since the equipment that are connected between Phase to Neutral will become between Phase to Phase ( R to Y,Y to B), and since they are not of the same ratings, the artificial resulting neutral will be floating, such that the voltages present at the different equipments will no longer be 240V but somewhere between 0 (not exactly) and the 440 V (also not exactly).

Meaning that on one line Phase to Phase, some will have less than 240V and some will have higher up to near 415. All depends on the impedance of each connected item.

In an unbalance system, if the neutral is disconnected from the source, the neutral becomes floating neutral and it is shifted to a position so that it is closer to the phase with higher loads and away from the phase with smaller load. Let us assume an unbalance 3 phase system has 3 KW load in R-phase, 2 KW load in Y-phase and 1 KW load in B-phase. If the neutral of this system is disconnected from the main, the floating neutral will be closer to R-phase and away from B-phase.

So, the loads with B-phase will experience more voltage than usual, while the loads in R-phase will experience less voltage. Loads in Y-phase will experience almost same voltage. The neutral disconnect for an unbalanced system is dangerous to the loads. Because of the higher or lower voltages, the equipment is most likely to be damaged.

Here we observe that Neutral Floating condition does not impact on 3 Phase Load but It impacts  only 1 Phase Load only

There are Some Point needs to be consider to prevent of Neutral Floating.

a) Use4 Pole Breaker / ELCB / RCBOin Distribution Panel

A floating neutral can be a serious problem. Suppose we have a breaker panel with 3 Pole Breaker for Three Phase and Bus bar for Neutral for 3 Phase inputs and a neutral (Here we have not used 4 Pole Breaker). The voltage between each Phase is 440 and the voltage between each Phase and the neutral is 230. We have single breakers feeding loads that require 230Volts. These 230Volt loads have one line fed by the breaker and a neutral.

Now suppose the Neutral gets loose or oxidized or somehow disconnected in the panel or maybe even out where the power comes from. The 440Volt loads will be unaffected however the 230V loads can be in serious trouble. With this Floating neutral condition you will discover that one of the two lines will go from 230Volts up to 340 or 350 and the other line will go down to 110 or 120 volts. Half of your 230Volt equipment will go up in high due to overvoltage and the other half will not function due to a low voltage condition. So, be careful with floating neutrals.

Simply use ELCB, RCBO or 4 Pole Circuit Breaker as income in the 3ph supply system since if neutral opens it will trip the complete supply without damaging to the system.

Whenever neutral fails in three phase system, the connected loads will get connected between phases owing to floating neutral. Hence depending on load resistance across these phases, the voltage keeps varying between 230V to 400V.

A suitable servo stabilizer with wide input voltage range with high and low cutoff may help in protecting the equipments.

Give higher Priority on Maintenance of  LV network  . Tight or apply adequate Torque for  tightening of Neutral conductor in LV system

A Floating Neutral (Disconnected Neutral) fault condition isVERY UNSAFEbecause If appliance is not working  and someone who does not know about the Neutral Floating could easily touch the Neutral wire to find out why appliances does not work when they are plugged into a circuit and get a bad shock. Single phase Appliances are design to work its normal Phase Voltage when they get Line Voltage Appliances may Damage.

Disconnected Neutral fault is a very unsafe condition and should be corrected at the earliest possible by troubleshooting of the exact wires to check and then connect properly.

Published at Electrical Notes & Articles

Related EEPs content with sponsored links

Get access to premium HV/MV/LV technical articles, electrical engineering guides, research studies and much more! It helps you

in your everyday life as an electrical engineer.

Jignesh Parmar has completed M.Tech (Power System Control), B.E (Electrical). He is member of Institution of Engineers (MIE), India. He has more than 20 years experience in transmission & distribution-energy theft detection and maintenance electrical projects.

The Voltages on main LT panel (Out going of transformer), the Voltages are balance d 600 ph to ph.But R to G is 600V,B to G is 13V and C to G is 575V.

Current readings on the starter are balanced.

Can anyone know the reason and how to address this

The break in the neutral wire from the distribution transformer to the domestic supply has caused extensive damage to so called smart appliances such as refrigerator with an electronic mother board, desk top computer, inverter, phone chargers and voltage stabilisers for all these appliances. A 4 pole mcb at the main switchboard might prevent such an event.

What is the effect on energy consumption of a three phase high load consumer due to floating neutral

At my single family house in Florida I have just had a problem with a bad Neutral from Electric supplier (FPL) into my home

the way I noticed the problem was I received a shock from metal shower handle when taking shower, lights flicker and AC Handler damaged blower motor

Now very concerned with the life safety of my house for my family and myself

Any other steps you can offer for me to have done as far as more grounds installed or something my electrician or FPL could do that would protect the home if that would happen again form FPL

thanks for any advise you can provide

FPL did come out said it was there bad neutral line and made repair to splice connector at transformer and supply line

This What We Call Comprehensive Informative Job

Can it be advisable to connect neutral point earthed of a 3-phase 3 limb core Potential Transformer in Switchgear Panel ? As Switchgear Panel is of metal sheet & Source Earthed is connected to the metalic body through conductor. If external current flow through neutral the flux of PT may increased & in turn Vol;tage also will be increased which may result failure of Insulation of pt & it may damaged . Please give your valuable opinion . Also suggest for connection of Multi-function 3-PHASE , 3-WIRE meter across PT

Neutral was floating at power pole and we were getting 308volts. I switched off all buttons, even with buttons off will there be problem to appliances due to floating neutral?

is neutral earthing in servo stabilizer will solve the problem of Neutral Floating. if we use the stabilizer between the mains and the load

Very nice explained and useful article

If we load to gen the neutral shocks but on nepa it is normal why?

Could you please clarify during occurence of a neutral alive fault, why only some consumers equipment are damaged with overvoltage while other consumers on the same phase do not suffer from equipment damage? (T-T system used in my country.)

I guess author made this point already Some customer will experience Overvoltage while some will experience Low voltage. This happens due to neutral line will be close to one of the lines. I think the lines in-phase will have overvoltage and out of phase will have low voltage.

Request you to kindly clarify what would be the immediate effect of neutral break on LV switchgear 4Pole MCCB, ACB or MCB will they get trip ?

Tell us what youre thinking… we care about your opinion!Please keep in mind that comments are moderated andrel=nofollowis in use. So, please do not use a spammy keyword or a domain as your name, or it will be deleted. Lets have a professional and meaningful conversation instead. Thanks for dropping by!

Prove that you are not R2D2. Solve some math:forty=forty four

on EEP Pro Premium membership and video courses & bundles with discount code

Subscribe to our Weekly Digest newsletter and receive free updates on new technical articles, video courses and electrical guides.

© 2021 EEP – Electrical Engineering Portal. All Rights Reserved

The content is copyrighted to EEP and may not be reproduced on other websites.

Leave a Reply