Floating Neutral Bad Experience

thanks for sharing, gain my knowledge and make me aware for this problem. im waiting comment for other expert

Floating neutral was a major problem in star-connected capacitor bank of our steel plant. It has an RVT to trigger the tripping circuit.

This problem can be eliminated by:

A. Hard wire the equipment to the power source which will eliminate the plug assembly.

B. Purchase and install a positive locking socket/receptacle assembly. Crouse Hinds, and Allen Bradley (to name a few) manufactures these.

C. Periodically go through the equipment/source power panels to ensure neutral buss, links, jumpers, ect. are torqued correctly.

In some plant there is a practice of using hand-lamp neutral connected to body of equipments.It saves cable.

Wow! Good job that isn't in British Standard 7671!

Its basically still done (unchanged for many years) here in older houses, neutral and earth/ground are bonded at the main supply box and everything runs off 2 wires.

I could not believe it!!

Hated it completely and rewired the house years ago as well as placing an ELCB (or whatever the modern name is!) on each incoming phase (x3).

The reason I believe was when houses were fed (many years ago!) via overhead cables with only 3 x 220v Phase to phase on 4 wires only, and they did not change much when the supply was changed to 3 phase, 220 volts phase to neutral, which is why my original mains box is up on the first floor.

They had only a 4 wire cable (3 x pahse and earth), instead of 5 wire (3 x phase, neutral and earth) which came basically only into new build houses. There is still no legal requirement to change it in older ones.....!!

Since then I have added a new (extra) mains box in the cellar and feed the old from the new, but run new cables from the new box whenever required.....

Its not a dissimilar problem to my big gas tank in the garden. When I had it installed, I insisted on two regulators, one on the tank (normal) and one on the garage wall on the way to the house. The installer pooh poohed the idea with "if you want to waste your money!" attitude.

Since then, the gas company in Mainz had a couple of daft engineers who instead of supplying 50 Millibar to a row of houses, gave them 8 Bar (over 100PSI I believe)... They blew all the houses up and killed a little girl.......

Since that episode, all houses must have their own reducer if they are on "town" gas and two reducers if on a Tank......

Simple common sense does not always prevail here till someone dies....

G'day Mr Slack

Not being cheeky here, but in Aus, we do it to AS3000. What is the British standard..? 7671

MEN....?

Cheers.

Mark N.

PS. This Question is submitted as SERIOUS, and in no way, is meant to insult anyone,.

I do not know what BS 7671 is, and I am merely enquiring.

Very wrong and dangerous practice. In case of failure of earth / earth continuity the user of the equipment will be at life risk. The supervisors and foremen of the installation must have a constant vigil on their electricians work practices. Never allow or encourage short cut in electrical systems.

There are plugs and sockets with an extra 2 pins, ( 3p, N ,E and 2 smaller pins., so a 7 pin plug)which can be used for a control circuit. ie not fully plugged in, no continuity in control circuit, can be used to isolate supply. No volt relay will do the same thing also, and possibly a little bit cheaper.

Plugs not fully inserted are a common operator problem, hardwire, is another possible option.

And yes, it is amazing, how a simple problem can take such a huge bite.

Cheers,

Mark N.

Hi Markone, yes that could be a good idea, but is doesn't take into account poor connections or deteriorating plug connections. But I think that there is a better way of over coming this problem, it just has not been invented yet, the idea is to monitor the resistance between the neutral and earth, if the resistance is higher than the acceptable limits it locks out the power to the control system (this would require a manual reset) or to monitor the potential voltage between the neutral and earth, if the voltage goes over an acceptable level, the control circuit is isolated and again requiring a manual reset.

The biggest problem that we have with my solutions is that the test is usually a high impedance test, that is until the load is applied. A piss poor neutral connection may work ok at a low current but will deteriorate as the current rises.

Cheers

Joe

If you install ELCBs (or the modern version of them where you are), you will find that they trip if the load ever gets unbalanced, usually because of phase to earth contact of some sort, where the current flows to the neutral point via the earth cable instead of the neutral cable (or via ANY path other than the neutral wire), but it would not surprise me to hear that it would trip under the circumstances you talk about. In Germany for instance, they trip at around 20 milliamps or so.....

No guarantee though that this will trip, I think it will - but......maybe a better qualified Engineer can chime in and help?

Instead of that, it must be possible to monitor the voltage between earth and neutral, at the device, and have some simple device that trips the power if the difference goes above a certain maximum value......maybe there are already some devices around for just such a problem, if the ELCB idea is not a reliable/safe enough solution.

I am sure that there are enough good electrical Guys here that can give you a FAR better tip or two than what I have, as I have been working out of this area far too long!!

Best of luck in getting a good fix as what you describe is really dangerous.....

G'day Andy.

Here in Oz, we do it the old way. MEN that is.

I presume......hope I've got this right, that you are talking about a 3 phase supply to the building. Most ELCB s here are 4 pole for 3 phase, and the neutral must be connected to the NEUTRAL point on the ELCB, if neutral is connected to a phase connection, then yes, we also experience balance problems. But otherwise, it is a good system. In the early days of 3 phase ELCB installation here in OZ, incorrect termination, was a huge problem.

One brand would be reading from L to R, say Ph, Ph, Ph, N. The electrician would install a bucketfull of these, and then one day the Electrical Wholesaler would get a supply of brand x, at a really good price. Our Bloody good Electrician ( no sarcasm or ill intent meant) would buy up big. Install them, and have all sorts of problems with these useless bloody ELCB's, cheap crap. Never do this again. Who is going to recompense me for me Time and trouble to exchange to the sort, that I had always used.

The different ELCB's were reading say L to R, Ph, Ph, N,Ph. GOTCHA trip.!!!

The usual problem of," I know how, the instructions are for someone who doesn't know."

Oz, tends to be a dumping ground for, european electrical stuff, we are only a small market at the end of the day.

Caused more than a bellyache for the Local manufacturers, which never numbered more than 2 or 3.

And yes, when there is a phase to earth fault, hopefully the ELCB will trip.

Otherwise, connected properly, phase imbalance , does NOT cause tripping when it shouldn't, only, a detected imbalance of current to earth... As it should.

Most ELCB's here are set at 80% of rated current, so a 30ma, is set at 24ma, this allows for all sorts of Variables that can and usually will happen.

At the end of the day most sytems are good, well at least as good as, how well we install, TEST, and maintain.

Not Testing is another story, and I have seen some very embarrassed Electricians, Engineers, in my time, and yes, I have been caught myself. It is not hard to do the wrong thing....!

Cheers All

In Safety.

Mark N.

Thanks for posting, but I am at a loss as to what or to whom your post was meant for.....were you intending to post to me? If yes, why?

We have 3 phase with 5 connections here nowadays, I like each phase to be over ELCBs (or whatever they are called in English, as I live in Germany and might have the name wrong), and to use 3 connections P N E on a 220VAC connection for domestic wiring.

I let a fully qualified master electrician do the work. The test button on each works fine, we have not had any unexpected dropouts.....in 4 years.

I thought I had explained previously that at one time, Germany had a 220 Phase to Phase system with no neutral, but that was changed to a 415 Phase to Phase many years ago, but they only slightly changed the wiring and did not add a 5th connection (earth).....which is why in a house neutral and ground are connected together in the main box (some houses have instead a link in every socket between N & G instead.....)

So it was in some ways (2 wire) similar to Aussie & S.African systems with a single phase and ground return to neutral/Earth.......real (under)ground, not a ground wire (except for the first few meters of course!), was that what you were referring to?

Here we always had the wire....also we bond all metal water piping in a house to the ground from the mains supply and also run an earth pit as well....

Happy?

G'day Joe,

Try this link as a starter.

http://www.bramco.com.au/templates/bramco_content_08.aspx?pageID=4952

Stuff is out there.

Cost becomes the dictator.

Cheers mate.

Mark N.

I once owned a farm near Bowen where the coldrooms and irrigation pumps were 3 phase. With balanced phase currents not much problem. The house was on A phase and the domestic water pump on C phase. Now that was ugly, whenever the pressure pump cut in the voltage to the house rose (lights went bright) and a lot of electronic gear died. When I fronted NORQEB (pre Ergon days) I told them there would be a bad neutral at the Tranny. They installed a sealed data logger so I wasn't shown the results (no proof no liability). Almost immediately they not only changed out the tranny but they broke the distribution circuit up using 4 trannies where there had been only one feeding all the farms along the road.

Strangely enough the problem went away. No compensation though.

US contributors may have some issues with your post and my response as the results are somewhat peculiar to the MEN system.