Current between neutral and ground (3 phase)

[SunshineHarvey7]

I’m working in a newly constructed office that has 3-phase power. I have a few questions based on my measurements:

 

1) In the main breaker panel, there is a large wire that ties the neutral buss to the ground buss.  What might cause a current of around 7 amps to flow through that wire (according to my clamp-on meter)?

 

2) Is it true that a significantly unbalanced load can result in a significant leakage to ground?

 

3) Does it seem crazy to stick one probe of a digital voltmeter into the soil and with the other probe touch the ground rod and measure 4-5 volts or more? After I soaked the too few inches of soil, the voltage dropped to around 2 volts. Some insist it should be even closer to 0 volts. What would you say?

 

4) Have you had good experience with copper plated rods? Or would you insist on solid copper?

[Gottfrid]

1. You do not need a neutral wire in 3-phase. ???? 

2. Yes!

3. I would say 2 volt is close enough to 0.

4. Always best with solid copper.

[Led Lolly Yellow Lolly]

Sounds like you have a reversed neutral/phase. If so, this is hazardous. Be cautious.

 

 

24 minutes ago, SunshineHarvey7 said:

3) Does it seem crazy to stick one probe of a digital voltmeter into the soil and with the other probe touch the ground rod and measure 4-5 volts or more? After I soaked the too few inches of soil, the voltage dropped to around 2 volts. Some insist it should be even closer to 0 volts. What would you say?

This is a symptom of what I describe above. Be cautious, disconnecting the ground rod will electrocute you. The 4 or 5 volts is due to the soil resistance causing step potential.

 

24 minutes ago, SunshineHarvey7 said:

4) Have you had good experience with copper plated rods? Or would you insist on solid copper?

All ground rods are copper clad steel

 

[Led Lolly Yellow Lolly]

31 minutes ago, Gottfrid said:

1. You do not need a neutral wire in 3-phase.

Final circuits DO need a neutral return for single phase appliances and the utility company always supply it from the transformer. It also doubles as circuit protective conductor on most systems.

 

 

 

[Crossy]

@SunshineHarvey7 can you post a photo of the panel with the lid off please.

 

That large wire is your MEN link and may have current flow depending on how your board is wired (it may actually be carrying the full neutral current).

 

Does the current continue with the main breaker off?

 

There is certainly potential for an open supply neutral (so return current is going via your rod).

 

Whatever you do please don't disconnect your ground rod, nasty things can happen if the supply neutral is actually open!

 

EDIT is there any current in the cable that goes to the rod itself??

[Led Lolly Yellow Lolly]

... you can just clamp read the rod itself to check. . . Unless it's buried in cement Thai style.

 

 

 

[Muhendis]

1 hour ago, SunshineHarvey7 said:

3) Does it seem crazy to stick one probe of a digital voltmeter into the soil and with the other probe touch the ground rod and measure 4-5 volts or more? After I soaked the too few inches of soil, the voltage dropped to around 2 volts. Some insist it should be even closer to 0 volts. What would you say?

By coincidence, I just happened to check my PEA incoming neutral to my ground rod yesterday. The voltage was a very satisfactory 21 mV. Incoming PEA supply was isolated. so the reading was the voltage difference between my gnd and the nearest grounded post. Some time ago, when there was a fault in a village transformer, that p.d. was in the region of 60 V and, thinking I had a house wiring fault, caused me no end of head scratching.

[Led Lolly Yellow Lolly]

Topics like this always make me worried about the OP as the hours pass with no update.

[Led Lolly Yellow Lolly]

6 hours ago, SunshineHarvey7 said:

I’m working in a newly constructed office that has 3-phase power.

It should be highlighted that what you are doing is very dangerous. One mistake can blow your face off from an arc flash, in addition to the risk of electrocution. Where is the electrician that installed this system? Please respond.

[OneMoreFarang]

45 minutes ago, Led Lolly Yellow Lolly said:

Where is the electrician that installed this system?

Maybe it's better to talk to another electrician.

 

Unfortunately in Thailand are many bad electricians. And, even worse, many useless inspectors who let those bad electricians get away with horrible work. 

[Rampant Rabbit]

Think yourslef lucky I  get a  lovely 21V  every  night when the streetlights  turn on in the road  thru my neutrals down to earth. Happens the second their road lights  go  on, Ive even gone and turned off the streetlights  via  their sensors to prove this at  night and turned them on in the day by covering the sensor so i know it aint my set  up.

Started 18 months  ago when they installed a  new transformer and  new  earth rods  all round my land for their network........excellent  job guys!! cue  disinterested  look when reporting to PEA  locally

[Rampant Rabbit]

57 minutes ago, Led Lolly Yellow Lolly said:

It should be highlighted that what you are doing is very dangerous. One mistake can blow your face off from an arc flash, in addition to the risk of electrocution. Where is the electrician that installed this system? Please respond.

probably find he  died  not  long ago due to electrocution!!!

[Rampant Rabbit]

5 hours ago, Muhendis said:

By coincidence, I just happened to check my PEA incoming neutral to my ground rod yesterday. The voltage was a very satisfactory 21 mV. Incoming PEA supply was isolated. so the reading was the voltage difference between my gnd and the nearest grounded post. Some time ago, when there was a fault in a village transformer, that p.d. was in the region of 60 V and, thinking I had a house wiring fault, caused me no end of head scratching.

same here except  this is their "new  install" difference 21v

[Rampant Rabbit]

6 hours ago, Led Lolly Yellow Lolly said:

Sounds like you have a reversed neutral/phase. If so, this is hazardous. Be cautious.

 

 

This is a symptom of what I describe above. Be cautious, disconnecting the ground rod will electrocute you. The 4 or 5 volts is due to the soil resistance causing step potential.

 

All ground rods are copper clad steel

 

Their is  another  type that PEA  use in the roads  here, they aint copper  look  like galvanised  steel not those  girly 3/8 rods, they are in cross  section like an "+" an about 20  times  thicker, I have some smashed in round the land mostly by each houses "<deleted>ter" waste storage seepage tank where the soils alwasy wet

[Rampant Rabbit]

5 hours ago, Muhendis said:

By coincidence, I just happened to check my PEA incoming neutral to my ground rod yesterday. The voltage was a very satisfactory 21 mV. Incoming PEA supply was isolated. so the reading was the voltage difference between my gnd and the nearest grounded post. Some time ago, when there was a fault in a village transformer, that p.d. was in the region of 60 V and, thinking I had a house wiring fault, caused me no end of head scratching.

How did  you resolve  that as PEA  here are disinteretsed in my nightime  only 21V PD?

[Muhendis]

8 hours ago, Rampant Rabbit said:

How did  you resolve  that as PEA  here are disinteretsed in my nightime  only 21V PD?

I didn't resolve it. I found out about the transformer when my wife mentioned, in passing, the PEA transformer work which was ongoing in the village.

There is a significant amount of electrical work going on in Buriram at this time due, I suspect, to increasing business and population density. Anything like a misbehaving transformer would be picked up quite easily by the engineers.

[Crossy]

10 hours ago, Led Lolly Yellow Lolly said:

Topics like this always make me worried about the OP as the hours pass with no update.

 

Yeah. It does seem to happen worryingly often, a post is made which could indicate a serious issue.

 

A few pertinent questions from other members to try to identify the issue, then nothing.

 

And depending upon his responses to the posted questions it's either perfectly normal or a major issue!

 

[Rampant Rabbit]

2 hours ago, Muhendis said:

I didn't resolve it. I found out about the transformer when my wife mentioned, in passing, the PEA transformer work which was ongoing in the village.

There is a significant amount of electrical work going on in Buriram at this time due, I suspect, to increasing business and population density. Anything like a misbehaving transformer would be picked up quite easily by the engineers.

Id  got  neutral  linked to earth at the box  here and  found out when touching the metal door  handle  of  my  house  after they changed the transformer with a lovely  warm  tingling feeling which started of "randomly", thought I was  going mad ..... after some poking around and  by guesswork thought  wonder  why it  only  happens at  night, finally worked out auto street  lights  in the road on sensor started it.  BY covering the senor in daytime i could trigger the fault. p.d  should be less than 2v but PEA dont  care.....wonder if a PD of 230v would make them. 

Before they  put the  new  transformer  i got 0.1 pd, problem is the  moo bahn street  lighting.

[Muhendis]

1 hour ago, Rampant Rabbit said:

problem is the  moo bahn street  lighting.

Yeah. You just can't trust them photons to do what they're told.

[Crossy]

44 minutes ago, Muhendis said:

Yeah. You just can't trust them photons to do what they're told.

 

I think there's a thread about the issue somewhere.

 

[Crossy]

@SunshineHarvey7 Problem solved (or a non-problem)? Or some test results to share?

 

We do worry when an electrical OP goes quiet!

[SunshineHarvey7]

22 hours ago, Crossy said:

@SunshineHarvey7 Problem solved (or a non-problem)? Or some test results to share?

 

We do worry when an electrical OP goes quiet!

Sorry to stress you guys. I appreciate your concern. No worries—I posted the questions just before a two-day road trip. Didn’t have a chance to read your replies until now. 
 

i won’t claim I would never do anything “stupid,” but I did read somewhere about the danger of lifting the ground wire, so I won’t be trying that!

 

 Will try to respond to other questions separately….

[SunshineHarvey7]

On 4/18/2022 at 3:11 PM, Crossy said:

@SunshineHarvey7 can you post a photo of the panel with the lid off please.

 

That large wire is your MEN link and may have current flow depending on how your board is wired (it may actually be carrying the full neutral current).

 

Does the current continue with the main breaker off?

 

There is certainly potential for an open supply neutral (so return current is going via your rod).

 

Whatever you do please don't disconnect your ground rod, nasty things can happen if the supply neutral is actually open!

 

EDIT is there any current in the cable that goes to the rod itself??

A short video of the panel is attached. 
 

My plan next week when I return is to go to the office when no other workers are there, cut the main breaker, and then check the current between the neutral and ground busses.

 

We actually haven’t TWO ground rods connected in series. (1) was installed at the time of construction, and the top was just under the surface of the sidewalk around the back of the building. That part of the building is sitting on about 1.x meters of fill dirt, so I recently requested that a second rod be installed in parent soil not far away. 
 

I have measured a small current (less than 0.25 amps) between the fire and second rod. I have yet to positively identify the cable that goes to the first rod, so I haven’t measured total current on the main ground wire. 

[bankruatsteve]

40 minutes ago, SunshineHarvey7 said:

A short video of the panel is attached. 

I think only QuickTime users can open that.  (Apple file)

[Crossy]

Yeah, I can't make the video work ????  

 

Photos are always a good bet ???? 

[Led Lolly Yellow Lolly]

2 hours ago, SunshineHarvey7 said:

I have measured a small current (less than 0.25 amps) between the fire and second rod. I have yet to positively identify the cable that goes to the first rod, so I haven’t measured total current on the main ground wire.

Really I wouldn't call that a small current. Assuming they're bonded (which they absolutely should be) there should be nothing flowing. I really think you have serious issues here but I'll wait for some pics.

[SunshineHarvey7]

Here is a photo and video. Note in the photo that the ground buss is on the right, and the neutral buss is on the left, and the large wire that binds them together goes around the bottom of the panel.

[SunshineHarvey7]

28 minutes ago, Led Lolly Yellow Lolly said:

Really I wouldn't call that a small current. Assuming they're bonded (which they absolutely should be) there should be nothing flowing. I really think you have serious issues here but I'll wait for some pics.

If the voltage at the second ground rod is around 2-5 volts, and if the current going to that rod is 0.25 amps, then I suppose the power being dissipated to the second ground rod would be 0.5 to 1.25 watts. I have no complaints about that.

 

However, if the total current passing from the neutral buss to the ground buss is around 7 amps (as I noted above), makes me think the total power being dissipated is around 7 amps x 2-5 volts = 14-35 watts. (Not such a laughing matter.)

 

Another bit of info: Seems that one of the closest power polls to our office has a large steel cable passing from the neutral line at the top of the poll down to the ground. If the leakage we are getting is coming from outside our office (from "dirty power" thanks to someone else on our line), I'd be tempted to soak the ground near that steel cable to see if it would make a better "ground."

[Crossy]

30 minutes ago, SunshineHarvey7 said:

Here is a photo and video. Note in the photo that the ground buss is on the right, and the neutral buss is on the left, and the large wire that binds them together goes around the bottom of the panel.

 

Can you show where the incoming neutral (from the meter) first lands?

 

EDIT Hopefully the incoming N goes first to the ground bar (yes, that is correct for a Thai MEN implementation).

 

If it is like that then the 7A in the link cable is just the normal out of balance neutral current, you can verify by checking on the incoming neutral too (should be the same).

 

If it's not like that then Houston, we have a problem!

 

EDIT2 SMALL ground currents (actually diverted neutral currents) are normal in a TNC-S system with local rods and are nothing to worry about. We need to know what's flowing in that other rod.

[SunshineHarvey7]

2 minutes ago, Crossy said:

Can you show where the incoming neutral (from the meter) first lands?

 

1 hour ago, Crossy said:

 

Can you show where the incoming neutral (from the meter) first lands?

 

I circled where I think it is in yellow in the upper left corner.