Lighting Circuits with Floating Neutral

Its not an uncommon design by any means. I have seen similar setups used on 240 volt 3 phase delta systems before. If all of the lighting circuit loads are fairly equal in power consumption there is not a problem.

Even a moderate load offset in one phase still does not cause much concerns unless the load is grossly over the designed working capacity of that phase.

Given that by design electrical devices have a built in working range that make them tolerant to a plus or minus 10% or greater voltage variance its unlikely that even a heavily loaded phase will put that great of imbalance on the overall system.

Those may be some powerful big "ifs" and "unlesses." Ya sure, ya betcha, if the load imbalance is slight, so will be the voltage variation. However, weird load assignments could "dogpile" most of the lighting loads onto two phases, or even one.

Could you explain your reasonings and logic considerably further?

Where I am from 240 volt delta systems are common place. One phase is center tapped to provide a 120/240 split but still in that system the three primary 240 volt phase hot lines carry loads individually or in combinations with each other which in may cases can be considered highly imbalanced especially if its a three phase system where one entire leg is being produced as a phantom phase in relation to the other two.

Its quite often that the 120/240 volt phase may be carrying two to four times the power of the other two legs and yet no severe voltage imbalances occur in those systems from it.

This would depend to a great degree on context. A "small" consumer on an "infinite" bus would not experience much variation from nominal voltages. (The "dog" being plenty big enough to wag the "tail.") However, if the imbalanced loads are large in comparison to the supply (say a small transformer or a few gensets), then voltages can become out of range enough to cause problems.

Bad scheme. May be used, possibly, only in resistve (for instance heaters) loads, and with the condition that only one load is in each leg and the loads are of the same resistance.

What happens if there is more than 1 (parallel) load in each leg ? If 1 of 2 loads in let's say phase A fails (open), then there becomes more than 240V applied between the phase that feeds the remaining load and the neutral (and if it were 3 in each leg and there failed 2 in phase A then I bet there will be applied more than 300 V to the left load - whose nominal is 240V !)

As the matter of course, with the "earthed" neutral there is always 240V applied to each load.

"Grounded" - I thought the OP put it "earthed" - or not, when transformer's neutral is connected to the common point of the loads the latter always receive 240V.

A Floating Neutral System is not advisable, if the load changes due to failure of any light on the circuit you will shift the floating neutral, this would put more voltage on certain lamps in the circuit and could have a cascading effect of multiple failures.

I dont know what kind of lighting you are using, but I would not recomend this kind of installation anywhere.

Depending on the type of lighting you have in your installation, it will have varing effects, none of which are good, trust me on this mate.

The Other problem that you can get into is that the neutral is floating you can also get a potiental difference between the neutral and earth, this is also not advisable.

Fault finding would also be a bit more difficult in this situation.

Please tell me what kind of lighting you are using in this system.

Best Regards

Joe

How would you protect such a system with fuses ?

also would this system make rcds useless ?

also how would you fault find if possible fault could be on any one of 3 wires in either of 2 directions ?

what country is this system used ?

how would you fault find...?

Tornado can find fault with anything.

Sure! In this case, I could hook up some ground fault indicator lights, and at least narrow the problem down....

It is not a good system. In fact floating neutral system is not recommended for the following reasons:

1) Incase of unbalance of loads between the phases , there will be volatage unbalance ( i.e. shifting of neutral ) which may cause low voltage between two phases and higher voltages in other two phases causing damaging of equipments/ appliances.

2) In case of ground fault in any equipment/ appliance, as the neutral is not grounded, ground fault current finds no path to flow and circuit breaker will not trip under ground fault condition which is very dangerous condition and in violation of Electrical Safety.

3) As the neutral is not grounded, RCD cannot be operating which is again in violation of Electrical Safety.

Earlier we were having ELCB in in main ckts(3-phase) but it was frequently tripping.So we removed the main ELCB,but still the individual ckts( 2-Phase) are having ELCBs.And it is working fine.So i am not clear with your answer.

Earlier we were having ELCB in in main ckts(3-phase) but it was frequently tripping.So we removed the main ELCB,but still the individual ckts( 2-Phase) are having ELCBs.And it is working fine.So i am not clear with your answer

Isnt this the same as replacing fuses with steel rods to stop them blowing

and instead of repairing faulty circuits removing rcds

Unbelievable

you didn't understand my point,Still all the ckts are protected with ELCBs.Main ELCB we removed because that was tripping but rarely,means when we checked all ckts no earth fault was found and it was getting started without any tripping.Whenever it happened no earthfault came in picture.Finally we removed it .Means there was no earth fault.But what may be the reason

Means there was no earth fault. But what may be the reason

Well that's because there's no earth is there? and no Neutral either.

what your system uses is the sine wave of ac in that the voltage is constantly

going forward and backward quite a novel system really

But if there is a phase shift in any of the lines this would cause a large imbalance and this is possibly the cause.

The cure Hmmmm now there a thought poss make sure all light (light load that is) is using one pair

a better way might be to use a 3 phase to 3 phase isolation transformer this should equalise the surges if they occur

Any thoughts from other more qualified users?

Multi-phase transformers

A further complication lies in the property of the three sine waves of the three-phase system to 'cancel each other out' enabling a three-phase system the ability to operate without a neutral wire.

In a similar way, a three-phase transformer is designed often with three limbs only, so that the three fluxes - which follow the voltages - also 'cancel each other out'.

Unfortunately, this cancelling is true only at the fundamental frequency of the supply (50Hz in the UK). Most transformers are

controlled by thyristors in the 'phase angle' mode, which means that the current in the windings consists of a range of odd harmonics; dominant amongst which is the third harmonic, (setting aside the fundamental). Reference to Figure 3 will demonstrate that, far from 'cancelling out', the third harmonics reinforce each other. This

property can have interesting effects on a transformer core, resulting from overheating, since the flux will try to 'close' via any

metal in the vicinity - frequently the steel case.

There are two easy ways to avoid difficulty. The first is to wind the primary (usually, though the secondary is equally suitable) in 'delta' so that the three fluxes will add in a ring round the core, with a resultant of zero. The alternative is to use a five-limb transformer -

the outer limbs forming the return paths. These are not the only way to avoid a problem, nor is it guaranteed that they are always satisfactory. However, they are the most usual and fail only in very unusual cases.

There are many installations which have been running without problems for years which do not employ a delta. For whatever reason, whether it is because the transformer is lightly loaded or the third harmonic content is low at the normal working point, or a combination of other factors, these systems emphasise that the rules concentrating the third harmonic are only guidelines.

so hopefully this will solve your problem or at least point you in the right direction

So an ELCB, will measure the imbalance of current flow., usually. in a 3 phase system, through 4 legs.

There is now a wire, that you call neutral ,that is "floating", not hooked to anything and the current through this conductor equals the current through the 3 phase conductors.

How do achieve a current flow.

If your lamps are working, then it means that your "Floating Neutral" is not "Floating" anymore. More than likely it is earthed , somewhere.

If the neutral is not earthed, how does an earth leakage circuit breaker , work....?

If, all else has failed, did you have your "so called floating neutral" connected to the correct terminal on the ELCB. If you have a phase and neutral ,arse about, it will TRIP, on phase imbalance.......not earth leakage.

I really can not understand why you would try to re-invent the wheel here.

Though if your intent is on maiming and killing, then, I really think that you are on a winner.

The other thing is, in reply to your question, some well intentioned and helpful people have asked you some questions, to, I would say,to better help you.

Do NOT, do yourself a favour and answer those questions. Insult those helpful people, and ignore them, and make sure that they never really feel the need to ever try and help again.

Cheers.

Mark N.

Mark,

I have looked at a lot of your previous threads, Nothing that i have seen has made any sence.

Are you sure that you are a retired electrician?

This is not presonal, but since you decided to insult my integurity, I decided to have a look at you replys to the threads. They don't make sence!

Can you please explain, why you are so off topic?

Best Regards

Joe

Such an installation does not comply with British Standard 7671, so no UK Electrician could certify it, and the installation would not achieve sign-off under Part P of the Building Regulations as a consequence. The next step is for the insurance provider to withdraw cover for fire and electric shock, and the Local Authority to block any attempt for the freehold of the building to change hands. So it's better to do it properly instead before someone gets killed, really. Such events do tend to incur the wrath of the Health & Safety Executive and prosecution for Manslaughter is something worth avoiding.

PWS,

GA for you.

I do not understand people leaving out the earth connection. It's wot keps us safe!

Sleepy