High and low voltage 3 phase system

[refael]

Hey guys wanted to post a very interesting situation I've come across maybe someone will know more about it.

This is a 3 phase system with a neutral and earthing via ground rod

When I test beetween all phases and neutral or phases and earth everything is normal
However there is one circuit that when turned on causes the voltage on one phase to rise and one phase to go lower (im talking a 30 to 60 volt difference) this changes acording to what you plug in. The heavier applience the bigger the drop.
It also causes a potential of anywhere up to 40 volts depending again on how heavy the load.
If anyone here would have any ideas of what could have caused this will really appreciate any help.

If you need any more details feel free to ask and as a side note i asked the homeowner to get a 2nd opinion however unfortunately the electrician wouldn't listen to the testing i had done and is convinced its an earth problem on the whole house (which it obviously isn't because when the circuits off everything reads normal)

Thanks refael

 

[Andy™]

dodgy neutral most likely

 

[refael]

dodgy neutral most likely

I thought it might be an open neutral but tested fine and the actual circuits neutral has no issues of continuety

 

[kerching]

Network loop impedance test would be the next step

 

[poni]

I thought it might be an open neutral but tested fine and the actual circuits neutral has no issues of continuety

have you done a psc on each phase to neutral

 

[refael]

have you done a psc on each phase to neutral

The only thing is all the other circuits in the 3 story house are having no issues and this particular circuit is connected to the same neutral and the same phaze as other working circuits.

There is one other interesting find i forgot to post, the way the panels been wired theres 2 neutrals one connected after an rcd and one that's coming straight from the mains. (something if i can find the issue that would be rewired to include all circuits on the rcd)
When the rcd is switched off and that 2nd neutral bar is isolated (or should be) there's still a reading of 150 beetween phases and neutral there is no resistance beetween the 2 making me believe they're connected somewhere in the system (not in the panel, and after the breakers)
This tho wouldn't explain why one circuit would cause all the issues especially since the problem circuit is on the neutral thats overriding the rcd

 

[apprentice87]

Hey guys wanted to post a very interesting situation I've come across maybe someone will know more about it.

This is a 3 phase system with a neutral and earthing via ground rod

When I test beetween all phases and neutral or phases and earth everything is normal
However there is one circuit that when turned on causes the voltage on one phase to rise and one phase to go lower (im talking a 30 to 60 volt difference) this changes acording to what you plug in. The heavier applience the bigger the drop.
It also causes a potential of anywhere up to 40 volts depending again on how heavy the load.
If anyone here would have any ideas of what could have caused this will really appreciate any help.

If you need any more details feel free to ask and as a side note i asked the homeowner to get a 2nd opinion however unfortunately the electrician wouldn't listen to the testing i had done and is convinced its an earth problem on the whole house (which it obviously isn't because when the circuits off everything reads normal)

Thanks refael

Hi there,

Two points..

1, As has been said, you DEFINITELY 100% have a faulty neutral, so you need to get the DNO as soon as possible.. Depending on the load and how bad the neutral is, you could well see the voltage on one phase dropping to zero, and the full phase to phase voltage [as in about 415V] appearing between another phase and neutral, which will obviously destroy any connected loads in the house.

2, Just as well it is a TT earth, as, if it were TNCS, due to the neutral fault, the earth voltage would rise in line with the volt drop across the neutral fault. Testing in the house would reveal nothing, as it is all bonded together, but if you were to go and stick a screw driver in the ground out in the garden and measure between earth and that, you would definitely have a voltage that varied according to the load applied to the system. This would be a very dangerous fault, as you could well see full mains voltage appearing on the earth at some stage. Again, you might not notice in the house, until that is, you touch earthed metal work and stand on a bare concrete floor with bare feet, in which case you could well fall down dead.. If the fault were downstream of you, you could very well find the neutral current from other properties down the road, returning through the ground, up your earth rod and back through YOUR neutral.. So, count yourself lucky it is not TNCS!!

Anyway, you need to get the DNO. If it were me i would tell then that it was a TNCS system as they will come out well quick then!

john..

 

[UNG]

Hi there,

Two points..

1, As has been said, you DEFINITELY 100% have a faulty neutral, so you need to get the DNO as soon as possible.. Depending on the load and how bad the neutral is, you could well see the voltage on one phase dropping to zero, and the full phase to phase voltage [as in about 415V] appearing between another phase and neutral, which will obviously destroy any connected loads in the house.

2, Just as well it is a TT earth, as, if it were TNCS, due to the neutral fault, the earth voltage would rise in line with the volt drop across the neutral fault. Testing in the house would reveal nothing, as it is all bonded together, but if you were to go and stick a screw driver in the ground out in the garden and measure between earth and that, you would definitely have a voltage that varied according to the load applied to the system. This would be a very dangerous fault, as you could well see full mains voltage appearing on the earth at some stage. Again, you might not notice in the house, until that is, you touch earthed metal work and stand on a bare concrete floor with bare feet, in which case you could well fall down dead.. If the fault were downstream of you, you could very well find the neutral current from other properties down the road, returning through the ground, up your earth rod and back through YOUR neutral.. So, count yourself lucky it is not TNCS!!

Anyway, you need to get the DNO. If it were me i would tell then that it was a TNCS system as they will come out well quick then!

john..

Do they have DNO's in Israel?

 

[binky]

Do they have DNO's in Israel?

I hadn't noticed that - anyone any idea what their electrics are like?

 

[Andy™]

I hadn't noticed that - anyone any idea what their electrics are like?

well the problem is the first post is probably normal

 

[refael]

Im actually originally from uk Manchester in fact and the electrics here besides being done more sloppily here is no different to England

 

[refael]

I

Hi there,

Two points..

1, As has been said, you DEFINITELY 100% have a faulty neutral, so you need to get the DNO as soon as possible.. Depending on the load and how bad the neutral is, you could well see the voltage on one phase dropping to zero, and the full phase to phase voltage [as in about 415V] appearing between another phase and neutral, which will obviously destroy any connected loads in the house.

2, Just as well it is a TT earth, as, if it were TNCS, due to the neutral fault, the earth voltage would rise in line with the volt drop across the neutral fault. Testing in the house would reveal nothing, as it is all bonded together, but if you were to go and stick a screw driver in the ground out in the garden and measure between earth and that, you would definitely have a voltage that varied according to the load applied to the system. This would be a very dangerous fault, as you could well see full mains voltage appearing on the earth at some stage. Again, you might not notice in the house, until that is, you touch earthed metal work and stand on a bare concrete floor with bare feet, in which case you could well fall down dead.. If the fault were downstream of you, you could very well find the neutral current from other properties down the road, returning through the ground, up your earth rod and back through YOUR neutral.. So, count yourself lucky it is not TNCS!!

Anyway, you need to get the DNO. If it were me i would tell then that it was a TNCS system as they will come out well quick then!

john..

I disconnected the neutral from the panel to test beetween neutral and phases and there was no issue there.
it would seem like a neutral issue but don't see how its happening because its only the one circuit which is bonded to other circuits on both live and neutral in the panel, which is causing the issue.
After further testing i think it's flowing beetween 2 phases instead of to neutral i just dont understand why especially since the other circuits are using the same neutral.

 

[refael]

I wouldn't say this is normal in israel they definitely has a lot of issues with the wiring mainly due to the mentality here of if it works it works

well the problem is the first post is probably normal

 

[binky]

I wouldn't say this is normal in israel they definitely has a lot of issues with the wiring mainly due to the mentality here of if it works it works

Daft question but do you have a 3 phase head? Might be worth checking it is 3 phase and not only 2 phases.

 

[refael]

Daft question but do you have a 3 phase head? Might be worth checking it is 3 phase and not only 2 phases.

Its definitely 3 phases

 

[apprentice87]

I

I disconnected the neutral from the panel to test beetween neutral and phases and there was no issue there.
it would seem like a neutral issue but don't see how its happening because its only the one circuit which is bonded to other circuits on both live and neutral in the panel, which is causing the issue.
After further testing i think it's flowing beetween 2 phases instead of to neutral i just dont understand why especially since the other circuits are using the same neutral.

Not a clue what you mean here..

Go test the voltages phase/neutral at the origin of the supply. Now apply a load and measure the voltages at the origin once again. What happens??

In a BALANCED three phase load, this is NO current in the neutral. You go applying an UNBALANCED load, [like a single phase load] and the voltages between the "other" two phases and neutral stay the same [0v] as neutral is connected to the star point at the transformer and also to earth.

If there is a problem with the neutral, as you drag the voltage down on the one phase [because of the load] the neutral will no longer be at 0v and all kinds of funny voltages will appear between the other phases and neutral. You can show this mathematically AND calculate the voltages on the other phases too, but at gone midnight i am not about to start doing that!!

john..

 

[refael]

Not a clue what you mean here..

Go test the voltages phase/neutral at the origin of the supply. Now apply a load and measure the voltages at the origin once again. What happens??

In a BALANCED three phase load, this is NO current in the neutral. You go applying an UNBALANCED load, [like a single phase load] and the voltages between the "other" two phases and neutral stay the same [0v] as neutral is connected to the star point at the transformer and also to earth.

If there is a problem with the neutral, as you drag the voltage down on the one phase [because of the load] the neutral will no longer be at 0v and all kinds of funny voltages will appear between the other phases and neutral. You can show this mathematically AND calculate the voltages on the other phases too, but at gone midnight i am not about to start doing that!!

john..

Hi
Thanks for the reply.
I understand what your saying and totally agree. However if there was a neutral fault at the mains it wouldn't be isolated to the one circuit, any time i plug something in the house, it should shift the load and cause the voltage to fluctuate.
However everything is completely fine until i turn on the breaker for this circuit. The only return for this circuit is the neutral which is connected to the same neutral bar as the other circuits And the phase its on is shared with other circuits.
The readings are all indicating voltage running beetween 2 phases instead of to neutral, I just can't figure out why this circuit is causing this.
Thanks,
Refael

 

[refael]

Not a clue what you mean here..

Go test the voltages phase/neutral at the origin of the supply. Now apply a load and measure the voltages at the origin once again. What happens??

In a BALANCED three phase load, this is NO current in the neutral. You go applying an UNBALANCED load, [like a single phase load] and the voltages between the "other" two phases and neutral stay the same [0v] as neutral is connected to the star point at the transformer and also to earth.

If there is a problem with the neutral, as you drag the voltage down on the one phase [because of the load] the neutral will no longer be at 0v and all kinds of funny voltages will appear between the other phases and neutral. You can show this mathematically AND calculate the voltages on the other phases too, but at gone midnight i am not about to start doing that!!

john..

When i said disconnected and tested the neutral i meant testing straight from the meter tails just disconnected so as to totally isolate the neutral from the system and see if it still read 230 (it did so it doesn't seem to be an issue from the power company side)

 

[binky]

Hi
Thanks for the reply.
I understand what your saying and totally agree. However if there was a neutral fault at the mains it wouldn't be isolated to the one circuit, any time i plug something in the house, it should shift the load and cause the voltage to fluctuate.
However everything is completely fine until i turn on the breaker for this circuit. The only return for this circuit is the neutral which is connected to the same neutral bar as the other circuits And the phase its on is shared with other circuits.
The readings are all indicating voltage running beetween 2 phases instead of to neutral, I just can't figure out why this circuit is causing this.
Thanks,
Refael

sounds like someone has linked between 2 ccts on different phases, borrowed a neutral or the like. It might be worth turning off the other breakers, turn on your faulty cct, and test at the breakers for a backfed voltage.

 

[kerching]

I see from your details younare in Israel
Is Israeli electric system the same as ours?
3 phase 230v to N
230 to earth
415 phase to phase

I know USA has some weird split phase. Hi leg, Lo leg malarkey of which I know nothing and care even less