Power Surge on 3-Phase Neutral Line

Easily remedied. Disconnect any two wires, with your eyes closed, jump as high as you can, twist in the air, stamp your feet twice, and reconnect the other way. Works every time.

Balance and draw on the legs without ground.

What do you really mean by "interlock".

Glad you didn't die.

Interlock used to be a 2D21 vacuum tube circuit, replaced by GFI solid state electronics, That was used in conjunction with 'Dead-man circuitry'. Interlock was the term used to give an impression that you could not get zapped. Wish I had a nickle. Major problem was the time delay between shut-down and lever arm to ground within an oil tank. Don't trust the 'Off' button, especially if there are capacitors involved.

Interlock is just a line that when connected to the equipment becomes a closed circuit, closes the relays in the power device and allows power to flow. So if there is no interlock between the power device and the equipment, there is no power. The relay has 3 lines that supply phase 1, phase 2, and phase 3.

..and thanks so much for helping

Balance and draw on the legs without ground.

Please explain more: Do you mean that I may not have grounded the piece of equipment correctly?

Thanks for your help.

Reactive (Inductive) loads in the three phases, classic Electrical Machinery Engineering.

I'd suggest residual power in some sort of capacitor elsewhere in the equipment or a crossed wire in another outlet, to another piece of equipment.

Al Gore would blame it on "man-made" global warming, PreZ Obama would suggest Bush caused it, Pelosi would flat out lie, Dodd would steal it, Barney Frank.. uh wait.. I've got to wash my eyes with Lye Soap for just thinking of that scum bag... And of course, Cheney would shoot it after he waterboarded it and told you what really caused the problem from info he received from the connector's enhanced interrogation.

http://mealercompanies.com

JL Mealer

There is a large capacitor in the equipment. but we have disconnected and connected to the equipment before without this happening. (when the capacitor would have been fully charged)

Hopefully ground was correctly connected....

Are you on a 110 volt system, 3 phase 230 volt phase to phase? I will assume yes for the moment.....or a 230/415 volt system?

Was the equipment truly 3 phase or not.

If 3 phase, the neutral is not actually required.....but may be supplied in the cable as far as the equipment.

If single phase (110VAC), (or multiple single phase) all the "return" current (bad description) MUST also flow down the neutral, that is why its there.....

As you haven't told us what the equipment is exactly, its difficult to be helpful.

If truly 3 phase, the neutral may have been connected incorrectly to ground or something.....and/or some sort of failure on the equipment.....really guessing here....

What if ground was not connected?

It was 115V 3 phase.

I will do some research on whether the equipment was truly 3 phase. It may not be because there is another way to power up the eq with single phase at a different connection point.

If you had 115volt 3 phase, you have single phase loads all running through the neutral. I in fact always add an extra neutral wire as often that wire is the same dimension as the phases, this means that (as here in Germany) you have an allowed max of 16 amps per phase, assuming all phases loaded, you have 3 x 16 = 48 amps flowing through the neutral = Normal business.

I do not know what your breakers are set for with 115Volts, but I assume around 30 amps per phase....= 90 amps on the neutral!!!

You can see why I add an extra Neutral wire........!

You also mentioned in another post that a cap was in circuit, if this was on the AC side, there will probably be little or no charge to talk about as the cap will be a non polarized AC type and being recharged 120 times a second!!! That should not affect anything unless of course it is defective......

One could discuss semantics that it had at one particular end a positive chage from before and when connected it was connected on a negative half cycle.....but I simply do not see a problem there....so whether it was charged or not and with what polarity is immaterial.....

Andy,

please go and read a bit about 3 phase supplies. you are giving this guy a bum steer. If he has 16A in each phase then he has NO current in the neutral. the only current present in the neutral will the the imbalance between the phases currents.

Chas

I think that you need to go and read up a bit, he is using 115 volts, that's developed between phase and neutral in the USA and other such countries.

Do remember that phase to phase is 230 volts.....or thereabouts.

He is using 3 x phase to neutral.......for items that only need 115 volts single phase. But 3 times, unless he himself does not have a clue what he has been telling us.....

If you had read my earlier posts more carefully, I actually mentioned that if he was using 3 phase, the neutral would not need to be connected anywhere.....as for example a 3 phase motor will use the 230 volts phase to phase, neutral unconnected.....and not needed.

The "bum steer" comes from your ranch......not mine!!!

If you wish to learn more about this, read here and inwardly digest my friend:-

http://en.wikipedia.org/wiki/Three-phase_electric_power

Here is the important paragraph that you need to fully understand, this says it all very concisely and in an easy to understand format. Many make the mistake you have done:-

Three-phase systems may or may not have a neutral 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).

Andy,

the temptation is to be insulting but I will refrain. He has a portable, or at least an unpluggable, apparatus that has three phases and neutral on the connector. The neutral may be there for several reasons.

1) the equipment has a control or program circuit that derives it's power from 115V. this is common in industrial washing machines, dishwashers etc.

2)the interlock referred to by the OP may need the neutral to enable the supply side contactor to switch power through the connector.

3) the load could be say three heater elements which switch off independantly and are connected star. they would then need the neutral to maintain 115V across each element.

BTW, 115V Ph-N = 199V line to line not 230V

It is actually more likely that he has (should have) 120V which would give him the standard 208/3 ph.

Regards

Chas

Hey guys,

Am I missing something. Don't I need neutral simply because there is never perfect 3-Phase??? If the 3-phase system is perfect then they cancel each other out. The 3 phase systems I have measured never have exactly the same voltage on all 3 phases. So the resultant power has to go somewhere, so it returns on neutral. I am not a power expert, so let me know.

Thanks PITB

Sorry, but wrong thinking. Look at the links I posted for full infos....

You seem to take what I wrote wrongly for some reason that I cannot fathom....

I work usually in a 230volt P2N area.....I wrote that instead of 208 volts for phase to phase.....big deal....

What I was trying to get over is that true 3 phase loads (motors and transformers for example), do NOT need a neutral UNLESS they are using only one phase (115 volts USA, 230 volts Europe...)

Somebody even mentioned connecting Neutral to a Wye connected motor. The reason being is that many people misunderstand the differences between the "Neutral point" of the three phases on a 3 phase Wye motor and the Neutral!!!!! They should NEVER be connected to each other, to that effect I posted a few good links that described it better and simpler than I could......

Perhaps you have misunderstood me? as all you mention are SINGLE PHASED LOADS THAT WOULD NEED A NEUTRAL.......

I have the feeling that you have not read all the posts through fully.......!

Have a great day anyway!

I believe 208/3 w N gives 117V to N

Now, now, girls... you're BOTH pretty!

LOL

Phase A was shorted to the shield then connected to the middle item. At that point phase A is shorted to ground. Now one phase is missing and neutral went high. There were no relays in the middle item to protect the end item from neutral (the relays were only between phase power and end item, not neutral and end item). So the neutral pin at the connector to the end item was HOT! They tried to connect to end item with a hot neutral, it arced sparked and smoked.

do ya think?

You should supply more information,

How much load is there normally on the neutral, is the machine 3 phase or 2 phase or one phase & neutral or 3phases to neutral??

The fact that the interlock did not disconnect power at the socket suggests a faulty socket has somebody worked on this socket and left it in a dangerous condition?Have you checked this?

Garth

i think the load which you have connected to the mains supply would be heavily unbalanced....which resulted in high current through the neutral wire...which might have melted it...

We have 100 of these pieces of eq which we connect to and disconnect to often. Just this one time we connected and this happened. Also, we connected to this piece of equipment 1 month ago and it powered up normally.

When you say the load is unbalanced, how does that happen?

Such connections are generally unbalanced as each phase has its own load.....which may be heavier or lighter....

The only fact that an unbalanced load can cause is that it can forge the neutral to rise above the ground, eg. if you connect an AC voltmeter between Neutral and earth you will have a relatively high reading. This can become dangerous insofar that a phase can have a then higher than normal voltage.....if this has anything to do with your problem, I could not say.....

At home, I am always careful to balance the loads equally on the 3 phases as far as possible, but many simply do not bother.....

see if you have a 3 phase load and impedances in every phase is equal(both in magnitude and in phase angle) then the given 3 phase load is balanced...then you will have no current in the neutral wire...if there is any difference in impedances then unequal current will flow through them which results in a neutral current(sum of those unequal currents).perhaps there moght be any short in any of the phases in the load which might have resulted in unbalance...this short may have happened due to high temperature which might have developed during last time operation...

Pain in the butt,

I presume by the interlock yoyu mean that you hav a six pin connector, 3 x phase, neutral , earth, and a pilot pin. The pilot pin is the shorest and connects last, returning neutral back to the contactor which switches the phases through. If that is the case then had you fully engaged the connector when this happened or did it happen "half in" If it happenend Before the pilot connected then you have a fault with the socket. If afterward then it is likely that you have a short circuit on one phase and the breaker is not working. Get a sparkie to check the supply side either way.

regards

Chas

Thanks capblanc.

I am trying to understand.

You say if I fully engaged the connector then there must be a short circuit on one phase. shorted to where? to neutral?

maybe I should check power rating of the neutral line.

I will have the facility pwer manager check the supply side.

Do please remember that if you have a true 3 phase load, the neutral is NOT required.

It is only required when powering 115 volt devices.....then and only then.....

God, I'm getting rusty.

Three phase to me was ground neutral and three hots.

Single phase no neutral, only ground.

If loads are imbalanced drawing on the hots say, on a 300 amp service, and one leg is drawing 40 amps, and the other 80, and the other 80, that's 100 backfeed. If the circuit is not grounded, voltage goes to the Neutral, and gets higher and higher as more and more draws are put onto the hots.

Typically over the years Andy Germany has demonstrated in many posts that he knows what he is talking about.

My experiences were with 110 120 devices, and sometimes I'd have to jab two legs of 110 into either an HMI Ballast for something like a 6K Movie Light, or a DC rectifier to get it to work and run a Zenon.

I really appreciate this sort of thread, since I discover I have simply forgotten some things.

As well I don't know why in a 220 system, called Three Phase, a neutral is not part of the definition?, whereas it is implied it is part of the definition working a 110/120 system?

I always appreciated the Plumbing Theories of Electricity, as if same as water, it wanted to go down the hill, and into the ground, back it up, or impede it, and it springs a leak, (Arces or explodes!), small pipe under great pressure, and you've got resistance. -Things get hot.

Certainly it is not recommended at all to hot stab either lights, or motors, and especially motors, since they are just sitting there doing nothing, and "resist" being rudely awakened.

This may well be why the wires were overwhelmed, since things worked without problem when power was off truly, prior to connections, and turning whatever machine we are talking about, on.

Look at the links I posted, they will help you in better understanding the differences.....

If I can answer any question for you, fire away.

load = flying pointy thing

OK so the load could be the problem. I will have the load torn down and inspected.

Thanks, that helps a lot!

Methinks playing with flying pointy thing (with bangy bits in front?) on needs to be very, make that VERY careful,

I have an inkling that there may be two faults, both in the load and the supply, or in the procedure.

be careful and lucky.

Chas

I think we maybe close to AHA!

Ok forget about interlock. I should have left that off. My guess is interlock was made and power was already allowed to flow. So at the moment of full connection is when the surge occurred.

Now, what if they did not have the piece of equipment tied to ground and the cap in the piece of eq was still charged from the last time it was powered up.

Can that cause a large power surge at neutral?

Here we go again... THIS IS IMPORTANT.

Let's just say for example: 'Mr. A' wired something up line of your connection, (perhaps in a seperate structure totally, yet on the same main breaker), and Mr. A
black wire to ground out or as a return (common).

You are now wiring the black wire to power up along with the red wire.

Mr. A had taken that same red wire and sent it as a return (common).

You used the white wire as hot as did Mr. A, so the power tested as good to go.

By the time Mr. A's wiring made it to your breaker, it had been used as 110 elsewhere and there was no error found (except maybe in the showers along the route when the water pipes took that black hot used as a ground... Gee, this is what is happening in Iraq too).

There is no other problem except someone incorrectly wired the connections up the power delivery line from where you are at. The same hot wire they used (Mr. A in my example) is being used as grounding out and affecting the water pipes, etc... and potentially hurting people in the showers, or those touching fire doors handles and knobs and hinges.

You can be the hero and bring this to the attention of the local building ispectors and then maybe call the Army and let them know why they are shocking the soliders in the showers... Just a thought.

JL Mealer

Mealer Companies, MealerAMC- America's next major automaker!

The MEALER will also provide 3 phase power to a home or office
or to national tent city (if Obama's economic plan keep sup) when it is parked.

http://mealercompanies.com

Mr. Mealer,

As soon as I figure out who, I will send your info up the chain. I am appalled at the soldiers getting electrocuted in the shower.

..but in my case, we are using a gas powered generator. powering only my tester and nothing else. My tester passed all self test, then was connected to UUT and then poof.

thanks for your help

PITB

Hi All,

Look at the link provided by Andy explains three phase quite graphically. If you go down a bit in the article you can see the animation showing how the currents cancel and the worst case scenario, all the load on one phase, the neutral will carry no more than the current in that one phase. If load is added to either of the other phases then the neutral current will reduce. Since this is so why would you double up the neural wire?

FROM TH WIKI LINK

• "The phase currents tend to cancel out one another, summing to zero in the case of a linear balanced load. This makes it possible to eliminate or reduce the size of the neutral conductor; all the phase conductors carry the same current and so can be the same size, for a balanced load. "

regards

Chas

That only applies to three equal, single phase loads.

This of course assumes that none of the three equal, single phase loads becomes unequal or the N would have to carry the same current as the lost phase. A cheap and dangerous assumption.

It has nothing to do with three phase motors, or three phase transformers. A VFD or other three phase rectifier type load should also be OK after inrush. None of these requires a N.

If the machine has a N in then there is almost certainly at least on single phase circuit in the machine. Probably control.

Hi GordieGii,

208/√3=120.09

The graphic does indeed only show a balanced load but it does demonstrate the fact that they cancel out thus, if a neutral were to be connected no current would flow. All well and good in theory but, as you say, what if some component does need the single phase voltage or the systm needs to protected from the neutral moing away from earth.

regards

Chas

Neutral is usually only connected to earth at the substation before the users.

Badly unbalanced loading of the phases will result in the neutral getting voltage on it at the customer fusebox. There are allowed limits which you will need to find out from your local supplier.....if you are interested.

These problems usually result in computer errors in big data centers (been there, done that and got the T-Shirt!)......due to problems of voltage between frame ground and system ground.....in extreme cases, they can get quite dangerous to mainteneance people. Spain has a lot of such problems......as does Portugal and London....

There are many good links to read on the web about this....Wikipedia is a good starting point.

...and the graphic doesn't show a N so naturally the currents will cancel out, they have nowhere else to go.

In a 3 phase system with no neutral wire, the "Neutral point" will move up a "leg" in a "WYE" configuration, when the loads are not exactly equal......

The leg it moves up is the leg with the lowest (highest?) load (though I am happy to be corrected here on this point as my memory is over 40 years old, sorry).......

A meter on the physical connection of the 3 phases (in a motor for example), would show a voltage reading above 0. A good example of how would be if some windings have been shorted together on one field coil, so taking more current on that leg.

This is not an answer to the problem but it may be a clue: so far no-one seems to have considered that this fault took place when a 3-phase connector was being inserted. It is quite possible that not all 3 phases connected at the same time, resulting in the worst possible imbalance, and the maximum possible current in the neutral line.

Have you read/followed the operators manual?

seriously, did this "black box" come with cryptographic instructions. we seem to be missing the forest for the trees (die walt fur der baumen, Andy)... shees. if you plug in your toaster that has worked before and it starts arcin' and sparkin' chances are that something has changed from the receptacle back to the power plant. but, if you decided to tape two knives to the cord and all of a sudden you get cooked, chances are that your improvised connection is not in accordance with the manufacturer. Keep things simple. maybe the replacement "thing" will have documentation...

PS NEVER let a "should have" replace a quick check with a meter when things are de-energized.

Just to clarify: There are 3 objects. The power generator, the tester, and the UUT.

The power generator runs on gas and is not connected to anything else except the tester. Self test was performed on the tester and the cables and all passed. Then the tester cable was connected to the UUT and just as connection was made ...sparking, smoke, and popping sound. Neutral pin from tester cable melted into UUT.

You all are a great help. From all you have told me I need to check for short in the UUT.

What is a UUT? you have not once explained what it does, how do you expect logical answers if you have not described the equipment? Also what piece of equipment would be designed to powered up when you push the plug in?

Possibly you had nothing more than a loose wire connection in the neutral socket of the UUT?? which arced out and burnt the whole thing up.

Garth man - please see post 24. Thanks for your help. PITB

you all are missing it.... you have your tester set to amps witch must be attached in sieries befor applying power ...if you touch probes of meter to any too legs in parellel...bada boom!!! you need to change your meter to voltage settings......from mrhemightdo.

Good discussion over a simple issue...

Through out this thread, I appreciate Mr.Capblanc's patient though intelligent explanations.....

Mr.Pain...you already got the answer...plz create a new thread if you hv any more queries...

Here, lot of mis-guidance is happening by some "Experts" to prove their "talents"...!!

To conclude...Nuetral is a standby element in a 3 phase circuit..If some imbalance occurs then only it acts.....

I vote for Mr.Capblanc...

<...What causes so much power on the neutral line?...Many safety features were mysteriously overridden in this case...>

Ordinarily the neutral would carry no more current than on a phase conductor. On a 3ø system with balanced loads, the neutral current is zero. However, some cables have a neutral conductor that is sized smaller than the phase conductors, to take into account the low neutral current.

One of the good bets for a melted neutral is an unintentional short circuit between phase(s) and neutral somewhere that has exceeded the current-capcity of the neutral conductor.

The safety features that requires immediate attention is the circuit protective devices in the phase conductors:

1. Carry out an examination of the cables, focussing particularly on the condition of the neutal conductor. If there is any doubt as to the integrity of this conductor, replace the particular cable with a new one. Chop any removed, damaged cable into short lengths prior to recycling so as to deter anyone from re-using it elsewhere.
2. Prior to either replacing or resetting the circuit protective devices, look for the phase-to-neutral fault(s) downstream of them with extra-low-voltage test equipment, and rectify it/them before any more damage is done.
3. Check that the circuit protective devices feeding the the main circuit and downstream subcircuits circuits are in good order and adequately sized to protect the cabling network downstream of them. Rectify all faults.
4. Once any phase-to-neutral faults have been eliminated, disconnect all loads from the system and carry out insulation test with a "Megger" or equal piece of test equipment.
5. Carry out an earth continuity check on all devices connected downstream of the main circuit protective devices.
6. Record the results of 4 and 5 above.
7. Having rectified all faults that the Megger has indicated, energise the system again by closing the circuit protective devices in sequence, starting with the main circuit protective devices and proceeding downstream until the entire network is safely energised.

This procedure should ensure no recurrence of the above-posted fault, and will give a high level of confidence that things are in order.

I've seen a lot of discussion about "shorted circuits". But there is little about unintentional "open circuits". Since an open circuit in a three phase system will cause a potentially severe unbalance in the load, the neutral current could then exceed the ampacity of the neutral.

Of course, we are all guessing because we have no idea of what kind of load is in use. I also looked for a discussion about 3rd harmonic distortion which I didn't find. I also wonder how much bigger the generator was from the connected load. I would imagine the generator didn't appreciate the large neutral current.