Current between neutral and ground (3 phase)

[Crossy]

10 minutes ago, SunshineHarvey7 said:

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

 

Are you absolutely certain!!!

 

Because if that is correct you have a very big problem!!

 

Do nothing more, get your sparks in ASAP!

 

Do NOT disconnect anything. Serious injury could result!

 

If you can find the connection to the other rod then by all means check the current there and check if the l,ink current goes away with the mains off.

 

What's the fat black wire at the top of the ground bar?

 

[bluejets]

1 hour ago, Crossy said:

Because if that is correct you have a very big problem!!

Neutral links on left hand side (2x) connected by a silver link so if main neutral goes there, that is correct to a degree.

Really the main N should go to the bottom terminal marked "N" to be absolutely correct.

Then, there should be an MEN link from any terminal on the neutral bar(usually adjacent) to the earth bar on the right hand side of the layout.

In many countries this MEN link would actually be an earthing conductor same size as the main earth to clearly define it as an MEN link that should never be disconnected under any power up condition.

With 16mm2 mains, this MEN link should be minimum 6mm2.

 

Actually what I see are 2 rather hefty SDI 's running to the earth bar (blue tape) which overall would be a big no-no and possible reason for the Op measurement.

 

Best this bloke doesn't stuff around anyhow and do as suggested, get someone qualified to check it.

As you say, open neutrals are a death sentence.

Edited April 20, 2022 by bluejets

[Led Lolly Yellow Lolly]

4 hours ago, SunshineHarvey7 said:

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.

Your maths is wrong. 0.25 amps at 220 volts is something like 60 watts depending on how long and thick the cable is. That sort of power flowing between bonded ground rods (as I understand your description of things) indicates something is seriously wrong. The only reason the voltage is being held down to a few volts is because it's buried in the ground. Think it through. It's just not something that should be happening under normal conditions.

 

EDIT: I just read the rest of the topic. Unfortunately CM is a 3 hour drive for me. You have serious, SERIOUS problems.

 

 

 

Edited April 20, 2022 by Led Lolly Yellow Lolly

[Led Lolly Yellow Lolly]

4 hours ago, SunshineHarvey7 said:

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.

This is normal. It's essential these connections from neutral to ground on the utility side exist for a TNC-S-MEN system to function normally and safely. You should be reassured that they exist. Your problems are unrelated to that.

 

 

Edited April 20, 2022 by Led Lolly Yellow Lolly

[Led Lolly Yellow Lolly]

4 hours ago, SunshineHarvey7 said:

I'd be tempted to soak the ground near that steel cable to see if it would make a better "ground."

I'd advise you to stop. Just stop. Stop stop stop :facepalm: You're the sort of guy we read about in the news. . . "Death by misadventure". You should stay well away from utility poles, especially in Thailand, especially in the rain. Stay away. Next you'll be sticking your tongue on the wires to see if you get a tingle.

 

 

 

Edited April 20, 2022 by Led Lolly Yellow Lolly

[Led Lolly Yellow Lolly]

. . . I also see what appears to be at least one <=2.5mm cable on a 32 Amp breaker. Also, what is that 10mm cable on a 40 amp breaker supplying, some kind of sub-main? (for sure that's a sub-main). . . and if so, it looks like the neutral for that sub-main might be derived from the ground bar of the MDB, and is there another ground rod on that sub-main with reversed LN??? .  . .

 

Honestly, I hate Chang electrical gear. I hate the way Thai electricians use non-standard colours for everything. I hate the way Thai electricians do just about anything and everything. I really, really hate it. It's sloppy, dangerous, and basically $#It.
 

 

 

Edited April 20, 2022 by Led Lolly Yellow Lolly

[SunshineHarvey7]

6 hours ago, Crossy said:

 

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.

Hopefully I can have our electrician come out and show me for sure which cable is the incoming neutral and which is the ground wire. 
 

You may not hear much from me for a week or so, but don’t worry…. I’m not planning any crazy electrical experiments! ????

[Crossy]

12 hours ago, bluejets said:

Really the main N should go to the bottom terminal marked "N" to be absolutely correct.

Then, there should be an MEN link from any terminal on the neutral bar(usually adjacent) to the earth bar on the right hand side of the layout.

In many countries this MEN link would actually be an earthing conductor same size as the main earth to clearly define it as an MEN link that should never be disconnected under any power up condition.

With 16mm2 mains, this MEN link should be minimum 6mm2.

 

Important Note :- The Thai implementation of MEN takes the incoming neutral to the ground bar first, then another link of the same size goes to the neutral bar (or the N side of the incoming breaker for single phase).

 

I don't have a 3-phase drawing, but this is how it's done for single-phase (PEA drawing, my translations).

 

 

In reality it doesn't actually matter for a 3-phase installation, incoming neutral to either the N or E bar is safe.

 

BUT

 

What IS a problem is that if the incoming N is on the left and our OP is measuring 7A in the MEN link! That means 7A is going down the rod. Why?? An open incoming neutral is the likely reason!! (a phase-neutral swap would be a lot more spectacular, ask me how I know ???? )

 

If the incoming N is on the right (where I would expect it to be for Thai MEN) then the 7A in the MEN link is just the normal off-balance neutral current and nothing to worry about.

 

 

[SunshineHarvey7]

6 hours ago, Crossy said:

 

Important Note :- The Thai implementation of MEN takes the incoming neutral to the ground bar first, then another link of the same size goes to the neutral bar (or the N side of the incoming breaker for single phase).

 

I don't have a 3-phase drawing, but this is how it's done for single-phase (PEA drawing, my translations).

 

 

In reality it doesn't actually matter for a 3-phase installation, incoming neutral to either the N or E bar is safe.

 

BUT

 

What IS a problem is that if the incoming N is on the left and our OP is measuring 7A in the MEN link! That means 7A is going down the rod. Why?? An open incoming neutral is the likely reason!! (a phase-neutral swap would be a lot more spectacular, ask me how I know ???? )

 

If the incoming N is on the right (where I would expect it to be for Thai MEN) then the 7A in the MEN link is just the normal off-balance neutral current and nothing to worry about.

 

 

I appreciate your taking the time to share a bit of the theory. I observed that the three-phase master breaker has no provision to shut off the neutral (cut the link between the incoming neutral/ground bus bar and the neutral bus bar per your illustration).

 

Regarding the location of the incoming neutral line (where it first lands), that was based on my uneducated guess. Sorry for raising an alarm before I have a chance to ask the electrician. (There are so many heavy wires that look similar that I can't be absolutely sure which one it is without asking the electrician.) Thus, it is possible that the incoming neutral is exactly where it is supposed to be. I'll update you when I find out.

 

Can you please explain what an "open incoming neutral" is?

[Crossy]

33 minutes ago, SunshineHarvey7 said:

I observed that the three-phase master breaker has no provision to shut off the neutral (cut the link between the incoming neutral/ground bus bar and the neutral bus bar per your illustration).

 

Yes, that's normal in 3-phase except under very particular circumstances. Switching the 3-phase neutral is pretty rare and it needs a special 4-pole breaker which closes the neutral first and opens it last when operated.

 

A broken or open circuit neutral can be very (very) bad news in a 3-phase system. In single-phase the power just goes off, in 3-phase you could end up with up to 380V phase-neutral which your 220V appliances really won't like.

[bluejets]

On 4/21/2022 at 2:38 PM, Crossy said:

In single-phase the power just goes off,

In single phase MEN an open neutral can be deadly as was the case a few years back in West Aus.

It can liven up any earthed equipment as it did in that particular instance and it left a teenage girl a vegetable for the rest of her life.

 

https://www.abc.net.au/news/2018-03-06/denishar-woods-suffered-brain-damage-from-tap-electric-shock/9520014

 

Thankfully open neutrals on the supply are usually rare.

In my 50 odd years as a lecky I would have come across possibly half a dozen cases.

First signs in days gone by were complaints of low light bulb brilliance or the frig cutting in and out, not running.

All were supply authority cabling related where the neutral connections were exposed to the elements.

These days the connections are grease impregnated plastic encased terminations housed in weatherproof mains boxes.

Edited April 22, 2022 by bluejets

[Crossy]

13 minutes ago, bluejets said:

In single phase MEN an open neutral can be deadly as was the case a few years back in West Aus.

It can liven up any earthed equipment as it did in that particular instance and it left a teenage girl a vegetable for the rest of her life.

 

https://www.abc.net.au/news/2018-03-06/denishar-woods-suffered-brain-damage-from-tap-electric-shock/9520014

 

Yeah, it blew up a row of cottages in the UK a few years back when the neutral current returned via the gas pipe!

 

The idea of all those earth points on the neutral is to keep the touch potential down to safe (ish) levels, it doesn't always work.

[carlyai]

Rightly or wrongly, that is one reason I did not earth my pool. All the litrature says you should have an earth strip, etc, etc. My feeling was that with all that double reo. in the cement and something happening with the power feed where all the current back to the transformer is looking for the easiest way to get there, it could be quite exciting swimming at that time. We have already had a suspected O/C neutral in the village, caused many problems and my AVR's started emitting that brown smell. So after a change of pants on my part, PEA fixed their problem, very quietly. 'No not us'.

[bluejets]

7 hours ago, carlyai said:

Rightly or wrongly, that is one reason I did not earth my pool. All the litrature says you should have an earth strip, etc, etc. My feeling was that with all that double reo. in the cement and something happening with the power feed where all the current back to the transformer is looking for the easiest way to get there, it could be quite exciting swimming at that time. We have already had a suspected O/C neutral in the village, caused many problems and my AVR's started emitting that brown smell. So after a change of pants on my part, PEA fixed their problem, very quietly. 'No not us'.

Yep...you are wrong.

As I said, open neutrals are rare and usually occur in older installations.

Nothing can protect against a badly maintained electrical system but what we have with the MEN is the best you will get.

Earthing pool structural steel included.

Those are the facts, if you don't like it, that's your problem but it doesn't mean the system is wrong.

Edited April 23, 2022 by bluejets

[carlyai]

2 hours ago, bluejets said:

Yep...you are wrong.

As I said, open neutrals are rare and usually occur in older installations.

Nothing can protect against a badly maintained electrical system but what we have with the MEN is the best you will get.

Earthing pool structural steel included.

Those are the facts, if you don't like it, that's your problem but it doesn't mean the system is wrong.

Ok, so why do you need to earth pool structures? It's a big Faraday's cage anyway. The pump is isolated from the pool, the lights are thru a special double insulated transformer at 12 V. So why tie the stainless steel ladders to earth? How are they going to get live? Maybe I will get worried if you have a good explanation.

Where I live it's not unusual for PEA to do stupid things, probably unintentionally. ????

[Muhendis]

2 hours ago, carlyai said:

Ok, so why do you need to earth pool structures? It's a big Faraday's cage anyway. The pump is isolated from the pool, the lights are thru a special double insulated transformer at 12 V. So why tie the stainless steel ladders to earth? How are they going to get live? Maybe I will get worried if you have a good explanation.

Where I live it's not unusual for PEA to do stupid things, probably unintentionally. ????

I don't know much about pools but is there not a possibility that the water can become electrified from a faulty pump?

I just thought the impeller is probably magnetically coupled so maybe not a problem.

Edited April 23, 2022 by Muhendis

[Led Lolly Yellow Lolly]

3 hours ago, carlyai said:

Ok, so why do you need to earth pool structures?

Swimming pools are a special case and it's a very big topic to tackle. You absolutely SHOULD be grounding the pool, but it's not that straightforward. The entire pool structure and it's surrounds (including metallic window frames, grab rails, absolutely everything) should be bonded together in one large equipotential zone. This includes the rebar of the pool structure itself. As for pool lighting this should all be on the other side of an isolation transformer. . .

 

Bare wet feet, bare wet hands, the risks are vastly amplified around pools. Skip any of this at your peril. It may work fine for 20 years, but then one day. . .

 

EDIT: I also just remembered, there is also the problem of galvanic rebar corrosion. Bonding the rebars helps prevent that by arresting small incidental currents flowing in the soil.

As I said, this is a really, really big topic to cover.

 

 

 

 

Edited April 23, 2022 by Led Lolly Yellow Lolly

[carlyai]

8 hours ago, Led Lolly Yellow Lolly said:

Swimming pools are a special case and it's a very big topic to tackle. You absolutely SHOULD be grounding the pool, but it's not that straightforward. The entire pool structure and it's surrounds (including metallic window frames, grab rails, absolutely everything) should be bonded together in one large equipotential zone. This includes the rebar of the pool structure itself. As for pool lighting this should all be on the other side of an isolation transformer. . .

 

Bare wet feet, bare wet hands, the risks are vastly amplified around pools. Skip any of this at your peril. It may work fine for 20 years, but then one day. . .

 

EDIT: I also just remembered, there is also the problem of galvanic rebar corrosion. Bonding the rebars helps prevent that by arresting small incidental currents flowing in the soil.

As I said, this is a really, really big topic to cover.

 

 

 

 

The pool structure is all bonded together because the double reo. In the base and walls are all tied together. It is one Faraday's cage. The difference is nothing is tied to the main earth. It's like a big cage sitting in the ground.

Also don't you need oxygen to rust? Used a vibrator to get the air out of the cement and all the reo. is enclosed in concrete.

I have only heard comments like 'you should' do this. No absolute reason. I had a reason for not earthing the pool structure and that was because of an O/C neutral with the PEA could cause a problem. 

I am not an electrician but when I built the pool I did a fair bit of research and consulted with this sites Guru. No one advised me not to earth the pool structure, it was my decision.

[Led Lolly Yellow Lolly]

You can lead a horse to water...

[Crossy]

9 hours ago, Led Lolly Yellow Lolly said:

Swimming pools are a special case and it's a very big topic to tackle. You absolutely SHOULD be grounding the pool, but it's not that straightforward. The entire pool structure and it's surrounds (including metallic window frames, grab rails, absolutely everything) should be bonded together in one large equipotential zone. This includes the rebar of the pool structure itself. As for pool lighting this should all be on the other side of an isolation transformer. . .

 

Bare wet feet, bare wet hands, the risks are vastly amplified around pools. Skip any of this at your peril. It may work fine for 20 years, but then one day. . .

 

EDIT: I also just remembered, there is also the problem of galvanic rebar corrosion. Bonding the rebars helps prevent that by arresting small incidental currents flowing in the soil.

As I said, this is a really, really big topic to cover.

 

 

This ^^^. Absolutely! 

 

Exporting of the TNC-S "earth" has become a hot topic in the UK, not because of pools (few have them) but the similar issue relating to EV charge points. It is essential that we avoid letting someone get between the TNC-S earth and true earth, there could be a significant potential between them.

 

Galvanic corrosion is not the same as rusting. It's a massive problem with DC powered railways, stray current from the traction return going via the structural steel can literally cause it to dissolve away leading to the inevitable. The rails which provide the return path for traction power are not actually "earthed" they are isolated to prevent stray current.

 

Anyway, we are way off topic here.

 

[SunshineHarvey7]

On 4/20/2022 at 2:58 PM, Crossy said:

Are you absolutely certain!!!

 

Because if that is correct you have a very big problem!!

Actually, as I think BlueJets suggested, for 3-phase service, it appears that the incoming neutral and ground wires are both connected at the right points, according to a mfr sticker I noticed inside the breaker box. 
 

 

i came into the office one day before most of the staff arrived. As all of the computers were off, and only some lights and a kitchen appliance were in use, only 1 of the three phases had a current exceeding 1 amp. I checked the current on the neutral/ground bonding (NGB) wire, and it was around 2-3 amps. 
 

Then I shut off the main breaker, which cuts L1, L2, and L3, and the NGB current dropped to zero. That led me to conclude that my NGB current is not due to other PEA customers or street lights, etc. 

 

i turned the master breaker back on, and later in the day when most computers and other requirements would be on, I checked the current on the NGB. Again, it was more than 5 amps. As I recall each of the 3 phases (L1-L3) had around 3-5 amps. 
 

Again, if those who have experience with 3-phases systems can say this is “normal,” I’m happy to let this issue rest. 

[Crossy]

You definitely seem to have significant diverted neutral current heading off down your ground IF it is wired as the diagram (I admit I'm still not convinced) you have a problem that needs looking at.

 

[SunshineHarvey7]

3 minutes ago, Crossy said:

You definitely seem to have significant diverted neutral current heading off down your ground IF it is wired as the diagram (I admit I'm still not convinced) you have a problem that needs looking at.

 

Know of anyone you’d recommend in the Chiang Mai area who knows 3-phase and might be willing to take a look?

[Crossy]

1 minute ago, SunshineHarvey7 said:

Know of anyone you’d recommend in the Chiang Mai area who knows 3-phase and might be willing to take a look?

 

Sadly no, we're down in BKK, a bit far to come.

 

Try a post in the Chiang Mai forum with a link to this thread, there could be someone who knows a competent sparks, or you could try your local PEA office, the chaps often like a bit of moonlight ????