Help needed trying to interpret neutral to Ground Voltage readings?

[gdhm]

I have asked questions in the past but am doing a new topic so as to not muddy the waters with a different query.

When our soi's power lines were upgraded several years ago (after 12 months of effort on my wife's and my part) we was getting summer/early monsoon season readings on my multimetre of 232V daytime non peak and approx. and 212Vpeak nightime AND I had a tiny current neutral to Ground rod (leak?) reading of 4 to 7 (max) Volts.

Last night I noticed the red (ground) LED my multiplug adapter that has a simple built in ground tester was glowing slightly brighter than expected. I rechecked my voltage with my multimeter (Peak 7:00pm) and Readings were 206V live to ground and 16V neutral to ground. I am assuming greater demand over the last few years is the reason for the drop in peak voltage HOWEVER, the doubling of neutral to Ground Volts from 7 to 16V had me confused. After 30 ins it slipped back to 11/12V and live voltage had improved to 210/212V

I woke at 3:00am and retested (2 aircons running) Live was 206V and Neutral 16V. I decided when morning came, to recheck and then switch off circuits to see if I could see anything notable. I woke 9:15am and BEFORE I started switching off individual fuse box circuits I retested voltage with my multimetre and got 226V (expected as non-peak and light usage time) BUT the neutral had dropped to 1V to 5V and has remained in that range till now 3­½ hours later. There were no appliances on/off at 9:30am that time that were not the same last night (and I have no reason to suspect any wiring or appliance issues in my house). Needless to say I did not precede to swithcoff indviduoa circuits as neutral to ground Volts back to norm (if not slightly lower)

Now I am totally confused! How can neutral to ground read 16V last night and a desirable low of 1V to 5V this morning/lunch time when I have NO changes in appliances being on/off?

I did not notice around 8:00pm last night that when voltage went up a little to around 212V (from 206V) that the neutral to ground dropped to 11/12V (from 16V)

Nothing has changed in my home system for years. My meter says on it it is a single phase 2-Wire 220V 30(100)A 50Hz class 2.0 Type FA33 M 150 rev/kWh. I knew we had a 30 Amp meter (PEA instruction when house built due to size of house (be there only 2 adults and 1 child living in it)

Does anybody have any logical explanations/conclusions and should I be unduly concerned?

My additional questions are :

1) IF amps are not a problem (I do not know how to test them) is 16V neutral to Ground an acceptable level for Grounding? If so how can it go up before Voltage would be considered unacceptable in an effective grounding rod sytem

I recall Crossey told me some time back that with a rod grounding system a a few volts are to be expected. 6/7V was my original norm but last nght I got a peak of 16V HOWEVER before in the past I never got less than 3V but today I got a consistent 1 V for a short period.

2) Is there any correlation between thre levels of Live voltage and Neutral top gorund voltage . I ask because the worst neutral to ground of 16V last night was when the Live was at its lowest of 206V and this morning/lunchtime when Live is up to 226V my neutral is down to 1/3/5V. (Currently at 12:45pm 224V Live and 4V neutral).

3) Is it possible someone else’s home wiring system is affecting/loading MY systems neutral to ground voltage or is that impossible?

Any suggestions conclusions on my observations would be much appreciated.

Many thanks all for your time.

Dave

[Lancelot]

In the US this was nick named "stray voltage."

Sixteen volts between the neutral (return) conductor and the grounded (earthed) wire is way too high. The problem could very well be outside your house, such as: poor/corroded connections and/or open neutral conductors on the electric distribution system. In the US, a greatly unbalanced 3 phase line would increase neutral currents and that sometimes contributed to stray voltage complaints.

On your side I would check, clean, tighten neutral and ground connections. Check your ground rod connections and resistance to ground. If the problem persists, you would need to contact the electric company.

This is a Wiki Stray Voltage link http://en.wikipedia.org/wiki/Stray_voltage

This is a Stray Voltage link on Youtube http://en.wikipedia.org/wiki/Stray_voltage

You are correct to be concerned and hope you find the cause soon. Based on the information in your post, I would not be suprised if the problem was on the electric company's side of the meter.

If you don't mind, let us know what you find

Edited June 20, 2013 by Lancelot

[IMHO]

In the US, a greatly unbalanced 3 phase line would increase neutral currents and that sometimes contributed to stray voltage complaints.

If it's not a problem with the ground on the OP's side of the fence, that ^ not only makes sense, but is unfortunately very common in TH.

[Crossy]

N-E voltage in a TT system varies with system load, it's caused by the volt drop along the resistance of the neutral.

If you measure 16V N-E when your own load is zero or very small there is nothing that you will be able to do about it as the problem is on the distribution network. Almost certainly an overloaded (or maximum loaded) local network.

The voltage will be greatest when the system load is high, so measuring at 3AM when everyone is asleep will yield the lowest N-E and measuring mid evening when everyone is home and drawing power will give the highest.

Also measure the L-N voltage (don't worry about L-E) as it's that which will cause problems if it's excessively low, and is something that MEA/PEA will understand and may do something about.

There is no hazard to life or equipment provided you have a decent rod and have RCD protection (essential on a TT anyway).

[Lancelot]

@IMHO. I'm wondering if there is a large load, operating at night, on the OP's distribution circuit, creating that unbalance.

Edited June 20, 2013 by Lancelot

[Crossy]

@IMHO. I'm wondering if there is a large load, operating at night, on the OP's distribution circuit, creating that unbalance.

Likely.

WARNING TECHNICAL CONTENT FOLLOWS

First, Google "ohms law"

Then. Consider this simplified distribution system:

The resistance of your supply cables is represented by Rl (live cable) and Rn (neutral cable).

The volt drop across Re due to the E current is very small (or zero) so effectively Vrn = Vne (which you are measuring).

The volt drop across Rn = N current x Rn = Vrn = Vne

When 'Other loads' is small Vne is small

When 'Other loads' increases Vne increases in proportion

So it is very likely that an 'Other load' is now connected somewhere on your local network and is pulling up the N-E voltage.

[gdhm]

Thanks for the input

I thanks those that have advised outside influences be the cause because that is was my opinion (if such a thing was possible). I stay in most days I use my PC I do not use an air con during the day we never\rarely change our habits for appliance usage within our house.

To be honest I see little point (unless something really drastic changed) to contact the local power authority because it took a year to get them to upgrade our power lines and they had ALL the visual & documentary proof they needed and they stonewalled (some even miss-spoke (PR word) to get us to go away. I feel there is no way they would be interested especially as readings are normal daytime and until I test over a week or so at night-time I cannot be sure how consistent the elevated N-E readings of 11V to 16V are.

I am not excusing myself from trying to remedy, just accepting reality and when hitting one's head against a brick wall is pointless (add to that NO other family in the soi or area is likely to ever test Electricity reading or be aware of them. My wife and I could not believe how 3/4 years ago they all accepted 175W at night (or less) when even fluorescent tubes (with older non electronic ballasts) struggled to fire up (if at at all on occasions).

N-E voltage in a TT system varies with system load, it's caused by the volt drop along the resistance of the neutral.

If you measure 16V N-E when your own load is zero or very small there is nothing that you will be able to do about it as the problem is on the distribution network. Almost certainly an overloaded (or maximum loaded) local network.

The voltage will be greatest when the system load is high, so measuring at 3AM when everyone is asleep will yield the lowest N-E and measuring mid evening when everyone is home and drawing power will give the highest.

Also measure the L-N voltage (don't worry about L-E) as it's that which will cause problems if it's excessively low, and is something that MEA/PEA will understand and may do something about.

There is no hazard to life or equipment provided you have a decent rod and have RCD protection (essential on a TT anyway).

Hi Crossy. In fact the N-E was at the 16V high 3:00am (not a low) but I live in Khon Kaen and quite a few houses around me have aircons.

me and the low volts approx. 206V at 3:00am same as early evening peak . I agree with you that early evening is the ultimate peak, BUT with the weather in recent months up here being so hot at night many people operate air-cons etc. all night and they really do use up the volts, so 3:00am being CURRENTLY having such high usage does not surprise me (we alone add 2 air cons to the load around 8pm.

I have ALWAYS found the quietest usage time here to be around 9:00am to late afternoon which I feel is because many people are out working or away from home during the day.

(e.g. It is now 2:15pm and L-E is 216V (fallen back 10V from 9:am to 12:30pm levels) BUT N-E is still only 4V (which I consider on the low end of my normal).

** ADDED later into this part of post: Well THIS IS INTERESTING (I think?) I am following Crossy's advice to measure L-N. It is now 2:45pm and the 12:30pm readings (only 30mins ago) have dramatically changed: L-E is now 210V (-6V) BUT NOW N-E 14V (up 10V).

Crossey L-N is /222V (big difference between L-N and L-E).

Which is my REAL voltage reading Crossy please, L-N or L-E

AND what is the significance for the very different readings between the two please (Just guessing but is it: N-E is approximately equal to L-E + N-E ?)

The local electricity around my area (Khon Kaen City) is always being stretched more and more Crossy (typical city and increasing population and housing). The local electricity authority seemed geared to maintenance or supply not improvement or bring under supply to correct levels unless pushed and pushed and pushed.(I speak from experience )

Had it not been for last night Ground Red LED being a little brighter than I have previously noticed when I switch off my PC I would not have considered anything out of norm. Today the N-E between 9:00am to 2:15pm was completely normal but not now at 2:45pm N-E is 13/14V (from 4V at 9:00am to 2:15pm)

All this suggests to me "outside influences & overloaded network" beyond my control (or ability to control).

Regards

Dave

[Crossy]

Dave. Your SUPPLY voltage (which your appliances see) is L-N.

Anything between 200 and 240V (roughly 10% about 220) is fine.

[gdhm]

@IMHO. I'm wondering if there is a large load, operating at night, on the OP's distribution circuit, creating that unbalance.

Likely.

WARNING TECHNICAL CONTENT FOLLOWS

First, Google "ohms law"

Then. Consider this simplified distribution system:

N-E volts1.jpg

The resistance of your supply cables is represented by Rl (live cable) and Rn (neutral cable).

The volt drop across Re due to the E current is very small (or zero) so effectively Vrn = Vne (which you are measuring).

The volt drop across Rn = N current x Rn = Vrn = Vne

When 'Other loads' is small Vne is small

When 'Other loads' increases Vne increases in proportion

So it is very likely that an 'Other load' is now connected somewhere on your local network and is pulling up the N-E voltage.

Hi Crossy I see you posted this whilst I was posting a reply. Thanks very interesting.

An embarrassing admission Crossy, "Out of sight out of mind" I had not got around to getting a RCD I assume that is what is called a Safe-T cut .

I am very embarrassed about that fact and WILL not forget or delay on your previous obviously very sound safetyadvice again. I will buy a Unit as soon as my pension pay day hits in 5 days time. Now I must find a proper electrician (vs a person who claims to be an electrician) - another part reason I stupidly delayed and let the matter slip.

I know you originally suggested I need a 100A unit to completely cover my metres capability but when I looked it was impossible to find a 100A unit being sold one up here. I can buy a 65A unit (which do not believe will be found wanting).

Are the main makes sold in Thailand In places like Global, Home Hub & Home pro essentially as good as each other, or do you currently consider any make preferable over others?

Will these N-E variations I am reporting between 4V and 16V cause the "Safe-T cut" to trigger shut downs? If so, what level should I set the sensitivity dial to?

My apologies for not having acted on your advice earlier but I promise I will this time and without further delay. I appreciate it must be frustrating to be asked for advice and then a poster not to quickly take up up relatively cheap and easy safety options.

Regards

Dave

[gdhm]

Dave. Your SUPPLY voltage (which your appliances see) is L-N.

Anything between 200 and 240V (roughly 10% about 220) is fine.

Thanks again Crossy.

That's reassuring. My volts are higher than I was thinking they were duirng the last 24 hours. I am sure I knew it wa ssuppode dot be L-N from previous need to test, but I had forgotten over time.

[Crossy]

The N-E voltages should have no effect on your RCD.

If it's adjustable set it to the lowest number that is doesn't nuisance trip, max 30mA.

[gdhm]

Sorry about typos in post #10 should be:

Thanks again Crossy.

That's reassuring. My volts are higher than I was thinking they were during the last 24 hours. I am sure I knew it was supposed to be L-N from my previous testing many months ago, but I had forgotten over time.

[gdhm]

The N-E voltages should have no effect on your RCD.

If it's adjustable set it to the lowest number that is doesn't nuisance trip, max 30mA.

Thanks Crossy that's great.

Probably a silly question

It seems the Safe-T cut site English pages links are broken or non existent however I screen dumped an interesting page months ago. The model here triggers for several things one being Leaks see image. Is this a different type of leak to that I am experiencing or is this unit not suitable for my system with its up to 16V on N-E or does that not constitute a leak

Sorry to be a pain with my lack of understanding but I do not wish to spend out on an item if not suitable that might trip "no matter what" on my system due to my N-E volts.

Edited June 20, 2013 by gdhm

[bankruatsteve]

What brand of CU do you have now? If it's Sneider Square=D you could just replace the main breaker with an RCBO. IE: it doesn't HAVE to be a SAFE-T-CUT to put front end RCD.

[gdhm]

What brand of CU do you have now? If it's Sneider Square=D you could just replace the main breaker with an RCBO. IE: it doesn't HAVE to be a SAFE-T-CUT to put front end RCD.

I was in the middle of this post when we had an area power cut GO FIGURE!!!. Come the Monsoon come the power cuts . Luckily today's only lasted about 20 mins and my UPS allowed me a controlled PC power down (love my UPS)

Hi bankruatsteve, thanks for your suggestion. Yes you guessed correctly I do have Sneider Square=Ds but I have 2 units side by side.

I have no idea how my two CUs are wired from the Metre. By that I mean, I know two cables come into and leave the outside metre but I do not know if if these are split to feed each of the CUs or whether whether they are "daisy chained" (I suspect daisy chained in view of how thick these cables are to splice into two, BUT I don't know what's normal to be honest I'm not an electrician)

Here are some photos of my CU set-up

It seems to me "in CU" replacement RCBOs are an easier option to fit (especially as the cable boxing above is not readily removable.

Am I correct in assuming these "in CU replacement RCBOs" have a single fixed trip threshold of the upper 30ma limit. If so, is that satisfactorily safe?

Should I fit 2 RCBOs (one RCBO in each CU)?

If so, then it seems an advantage coz if nuisance trips, or a real fault trip occurs then the whole house system is not shut down?

Are these "in CU replacement RCBOs" as safe as the big separate units?

Are there any downsides to "in CU replacement RCBOs"?

Thanks for yours and others help. Unlike this Forum I have great difficulty in trusting Local electricians advice I have so many times known more than the,y which should never be the case.

Regards

Dave

[bankruatsteve]

You can replace the main breaker (the one the big wires are connected to) with like a 45amp RCBO. You have a LOT of circuits (are you living in a resort? Or, a huge house? Rhetorical.)

Anyway, let's say one of the CU's is just for light circuits and AC's (for example). That could go without the RCD (in my opinion).

So, check what stuff (circuits) is in what CU and maybe just put the RCBO in one or the other. Or, both if you want.

Just looked at the photos again... the one with the yellow wires is all 16a breakers - probably light circuits. So, you might just put an RCBO in the other one but which might contain circuits that you really don't want to go out with a nuisance trip.

UpTU.

Edited June 20, 2013 by bankruatsteve

[bankruatsteve]

Another thought... if you want to get creative (with one CU RCD protected and the other not): you could swap out breakers from one to the other. Like if there is separate circuits (breaker) for things like washing machine, AC's, refrigerator, etc. stuff that will have ground protection anyway - you could move those to a non-protected RCD CU and put stuff you want protected in the other one.

[IMHO]

What brand of CU do you have now? If it's Sneider Square=D you could just replace the main breaker with an RCBO. IE: it doesn't HAVE to be a SAFE-T-CUT to put front end RCD.

I was in the middle of this post when we had an area power cut GO FIGURE!!!. Come the Monsoon come the power cuts . Luckily today's only lasted about 20 mins and my UPS allowed me a controlled PC power down (love my UPS)

Hi bankruatsteve, thanks for your suggestion. Yes you guessed correctly I do have Sneider Square=Ds but I have 2 units side by side.

I have no idea how my two CUs are wired from the Metre. By that I mean, I know two cables come into and leave the outside metre but I do not know if if these are split to feed each of the CUs or whether whether they are "daisy chained" (I suspect daisy chained in view of how thick these cables are to splice into two, BUT I don't know what's normal to be honest I'm not an electrician)

Here are some photos of my CU set-up

It seems to me "in CU" replacement RCBOs are an easier option to fit (especially as the cable boxing above is not readily removable.

Am I correct in assuming these "in CU replacement RCBOs" have a single fixed trip threshold of the upper 30ma limit. If so, is that satisfactorily safe?

Should I fit 2 RCBOs (one RCBO in each CU)?

If so, then it seems an advantage coz if nuisance trips, or a real fault trip occurs then the whole house system is not shut down?

Are these "in CU replacement RCBOs" as safe as the big separate units?

Are there any downsides to "in CU replacement RCBOs"?

Thanks for yours and others help. Unlike this Forum I have great difficulty in trusting Local electricians advice I have so many times known more than the,y which should never be the case.

Regards

Dave

They sure look like Schneiders (Square-D) to me - so in that case just replace the master breakers (left side of each load canter) with 30mA Schneider (Square-D) RCBO's.

As for whether they're relatively safe, my RCBO's saved me when the PEA upgraded us from a 15A to 30A meter, and flipped A <--> N.. Since being installed they've saved workers at least another 5-6 times, from everything from frayed cables on power tools to outright stupidity

Edited June 20, 2013 by IMHO

[Crossy]

Yup ^^^, Square-D RCBOs will plug in to replace your incomers.

30mA is more than adequate, particularly in a correctly grounded system.

[bankruatsteve]

Just to relate a recent experience regarding a L-N swap with RCBO: I was testing power circuits by connecting the CU to extension outlet (making sure correct polarity). This was using Square-D box with 30ma RCBO. After testing, I unplugged from the extension but left the wires connected to the CU. (my bad) So, while I was off packing wires into the box, one of the workers "helpfully" plugged my tester back in but reversed the polarity. Which I soon discovered when I got zapped by a neutral. !! Again, this circuit was "protected" by the RCBO so Sneider RCBO, at least, do NOT protect live N-E faults (or perhaps < 30ma?).

[IMHO]

Just to relate a recent experience regarding a L-N swap with RCBO: I was testing power circuits by connecting the CU to extension outlet (making sure correct polarity). This was using Square-D box with 30ma RCBO. After testing, I unplugged from the extension but left the wires connected to the CU. (my bad) So, while I was off packing wires into the box, one of the workers "helpfully" plugged my tester back in but reversed the polarity. Which I soon discovered when I got zapped by a neutral. !! Again, this circuit was "protected" by the RCBO so Sneider RCBO, at least, do NOT protect live N-E faults (or perhaps < 30ma?).

It quite literally saved my life - but I did get about 3 secs of half wave zap before I fell to the ground and made a path to earth (hand still firmly attached to the hot [should have been neutral] wire) - at which point the RCBO did it's thing...

I guess you could call me a living testament to them, but it did take several weeks for my cooked shoulder flesh to recover..

Edited June 21, 2013 by IMHO

[gdhm]

Hi Bankruatsteve, Crossy & IMHO,

Thanks Guys. I really appreciate your input and my knowledge and understanding grows with every post (as do my questions in some instances -SORRY guys!).

I have tried to address your latest posts in sections, but some comments may be in another section to try and group things)

Yup ^^^, Square-D RCBOs will plug in to replace your incomers.

30mA is more than adequate, particularly in a correctly grounded system.

Crossy

Am I correct in thinking that you feel this is the best or safe enough option for me? I will not change them personally although seem very easy, because I do not mess with electricity personally unless I can switch the power off and I know 100% what I am doing. I will certainly do not mess with disconnecting power lines from meter or those entering the CUs from the meter full stop.

I note you say "30mA is more than adequate, particularly in a correctly grounded system". Forgive me but can I ask about that comment. I believe my system is correctly grounded certainly all power outlets report a good Ground (except a few lighting outlets -see below.

My questions are:

1) Aren't RCBOs supposed to protect against a NO grounding situation or inadequate/faulty grounding?

2) Is 30mA not adequate in a poor/no ground system (I mean as far as sensitivity and purpose (not if there is a mechanical fault which of course would not then protect.

Other questions please about replacement RCBOs

1) Do you feel anything if you trip the RCBO at 30mA by physical contact?

2) a. Must it be Square-D RCBOs or are other makes also suitable?

b. If so are Square-D RCBO the preferable choice?

3) Are nuisance trips possible at 30mA or would a trip at that level of sensitivity signify a real problem?

4) I currently have 65A breakers in each of the CUs but people seem to be referring to 45A. Should I be downgrading to 45A)

I have no reason to believe the builder's electrician was entirely consistent in grouping circuits in the CUs I also believe he did (like SO MANY here) mix a light or 2 with a non lighting different circuit.

Unfortunately you can lead a horse to water but you cannot make it drink. I referred to you and this Forum prior to my build and found out the wire thickness's and fuses requirements for specific circuits and which should be on their own single circuit and made sure & CHECKED he followed those instructions to the letter . I insisted on grounding wires for all circuits (that was not 100% successful as he forgot to add ground wires to outside lighting and few down-lights.It seems felt not necessary for down-lights but I insisted he put them in when I found out he was not doing so. Mind you with one light I could not see how he could add a ground wire due to porgress of building without cutting though things but he (Said) he had managed to do so.

Hmmmmmm... Turned out the B*****D just pushed a green wire through the ceiling. When I changed an older ballast for an electronic one I it just fell out. That REALLY annoyed me, as my instructions to him and the Builder was very precise with the electrical wiring and in writing (all based on my knowledge and much of what you specifically and others had advised here to my questions (I did at the time think of or ask about RCBs/RCBOs). What can you do when a person lies and DECEIVES. I would have been OK with "I could not do that one because..." then at least I knew but to pretend there was a ground connection is in my opinion wilful criminal neglegence. I do find often over here that if an "expert" (I do not mean genuine expert) does not agree with an instruction they agree and then do their own thing rather than discuss or explain their logic. Hence why after my house building experiences I find it VERY hard to trust anybody (this D.I.Y Forum I DO substantially trust as advice has been sound and where a person has said something incomplete or accidentally in error, other quickly expand/correct.

I do know he used the correct thickness of wire for the power items water heaters, air-cons, Oven etc coz I personally kept an eye on him him with those and I know he put relevant items on their own single circuit & breaker.

I tested all the power points and other outlets for lighting I could get access to and indeed all the really important ones were indeed fully grounded (well what I think important anyway).

------

Bankruatsteve (LOL). Yes I have a large house & very oversized for my needs but what can you do when several family members planned or likely to live with us had change of plans at a late stage of building (which took a very slow 12 months).

One went to work in Denmark after a surprise invite to cook in a long term friend's restaurant. As she was the house owner 2 decided to stay in her house as they now felt like house owners one being the guardian of her niece - so she also stayed) & one at age 65 got married. reads like a comedy fiction doesn't it but its all true - end result I could have saved a lot of money had I guessed all this in advance.

The main reason I have so many breaker is because I erred on the side on caution (well that was my intention) and told the electrician to put certain outlets on a single breaker some 100% mandatory e.g. oven and two water heaters). Although we have 5 air-cons installed (2 in large main lounge) there is wiring for 2 other bedrooms and one downstairs spare room. I also ensured many power points in rooms on different walls . I assumed better to wire at house build time rather than maybe wish/try to add later.

Your comment ".....I got zapped by a neutral!! Again, this circuit was "protected" by the RCBO so Schneider RCBO, at least, do NOT protect live N-E faults (or perhaps < 30ma?)".

My questions:

1) should it have and would RCBOs normally protect live N-E faults do so or not? If you got zapped and it WAS under 30mA that does not sound good!.

2) Reversed polarity and testing. Do you mean by this, testing outlets to check that the live and neutral are consistently wired in all outlets around the house- which I have done and switched the wires around in a few outlets to make them all match ?

if you are not meaning this then I am misunderstanding something and would appreciate knowing. Thanks.

-------------

IMHO, Thanks for your info. That's very reassuring - I'd personally prefer to check RCBO functioning differently..... but hey each to their own LOL. I did not make my question entirely clear. Crossy had suggested (IF I bought a Safe-T Cut type device to set the sensitivity to as low as possible that did not allow nuisance trips to trigger. he mentioned 30mA was the least sensitively possible. What I was asking was at 30mA tripping could a person be harmed and how much would they feel if RCBO tripped.

I did get a Safe-T Cut installed in my wife's Aunt's house where I lived for a year. Her house is very run down and the wiring does not look good. The main breaker broke in my hand when I switched it off to install a replacement shower unit (I'm SOFT and HATE cold showers). It amazingly does not trip on it highest-but-one sensitivity setting, which is good. I did not know much about RCBOs but knew she had no grounding and needed a new switch - so I tried to play safe. I kid you not! the VERY NEXT DAY. BANG!!!!! my 3½ year stepson had found his Aunt's all metal tailor's scissors and decided to cut a thin 2 core extension wire. He knew nothing from his experience except the bang. So I know these units save lives.

Maybe divine providence that the main breaker broke off in my hand the day before?

What I did not appreciate was that when I got my house built, that a Ground Rod and wiring should still be supported by an RCBO as well. I mistakenly assumed a static ground rod was better than a mechanical option and that a combination was unnecessary. I did not know that a combination of both is advisable OR that rod grounding can really weaken if soil it rests in gets very dry etc. ANYWAY I KNOW NOW!! and I like the idea of double protection from electrocution from personal errors or electrical faults.

I DO worry about nuisance cut offs when I upgrade as I have a freezer, 2 fridges 2 water heaters and 5 air-cons all of which I assume would be the most likely to trigger an RCBO when I upgrade. To date I have never had a cut off in 5 years nor any problems with my wiring system (except low Volts to house at one time, and this 3-16V N-E voltage I have noted that seems to affect nothing.

Regards to all

Dave

[IMHO]

I'll try answering some of them

> 1) Do you feel anything if you trip the RCBO at 30mA by physical contact?

In the half dozen cases where workers tripped our RCBO, they felt nothing - and in one case that I witnessed the guy literally grabbed the live wire on a frayed cord, so would have felt a whole lot had there been no RCBO... The only case where someone felt something was me, when active and neutral were swapped around by an inattentive PEA worker.

> 2) a. Must it be Square-D RCBOs or are other makes also suitable?

Pretty sure it has to be Square-D (or at least something by Schneider) for your load centers. Willing to be stood corrected

> 3) Are nuisance trips possible at 30mA or would a trip at that level of sensitivity signify a real problem?

As far as I'm aware, Sqaure-D RCBO's are only available in two flavors: 10mA and 30mA, in TH at least. I've never had any false triggers with 30mA, but I have never used 10mA, so can't comment on that.

> 4) I currently have 65A breakers in each of the CUs but people seem to be referring to 45A. Should I be downgrading to 45A)

As far as I know, the biggest Square-D single phase RCBO in TH is 63A. Again, stand to be corrected The rating of the RCBO has to be correct for the total load passing through it - it does not have any impact to the "RCD" functionality of the device, just the Breaker part of it.

As for my zapping, it was actually a helper that handed be the live wire (unaware it was going to almost kill me).. not sure if the RCBO acted accordingly at first or not, but it definitely worked when I fell down!

Edited June 21, 2013 by IMHO

[gdhm]

Just to relate a recent experience regarding a L-N swap with RCBO: I was testing power circuits by connecting the CU to extension outlet (making sure correct polarity). This was using Square-D box with 30ma RCBO. After testing, I unplugged from the extension but left the wires connected to the CU. (my bad) So, while I was off packing wires into the box, one of the workers "helpfully" plugged my tester back in but reversed the polarity. Which I soon discovered when I got zapped by a neutral. !! Again, this circuit was "protected" by the RCBO so Sneider RCBO, at least, do NOT protect live N-E faults (or perhaps < 30ma?).

It quite literally saved my life - but I did get about 3 secs of half wave zap before I fell to the ground and made a path to earth (hand still firmly attached to the hot [should have been neutral] wire) - at which point the RCBO did it's thing...

I guess you could call me a living testament to them, but it did take several weeks for my cooked shoulder flesh to recover..

Glad you survived the unpleasant ordeal IMHO,

I thought RCBOs supposed to trigger within 25-40 milliseconds if current is flowing which I though can only happen if there is a live to neutral or ground pathway, which I thought would then trigger an RCBO in milliseconds.

Clearly I have much to learn. Seems to me you could have died before the RCBO triggered and it ONLY triggered when you thankfully fell making a pathway to Earth.

Dave

[gdhm]

EXTRACT...

> 4) I currently have 65A breakers in each of the CUs but people seem to be referring to 45A. Should I be downgrading to 45A)

As far as I know, the biggest Square-D single phase RCBO in TH is 63A. Again, stand to be corrected The rating of the RCBO has to be correct for the total load passing through it - it does not have any impact to the "RCD" functionality of the device, just the Breaker part of it.

My goodness IMHO that was quick reading and responding

Thanks for your several answers AND kind subtlety above. I have just rechecked and was mistaken. I can confirm I have 63A main breakers in each of my CUs

Regards

Dave

Edited June 21, 2013 by gdhm

[Lancelot]

I did not know that a combination of both is advisable OR that rod grounding can really weaken if soil it rests in gets very dry etc. ANYWAY I KNOW NOW!! and I like the idea of double protection from electrocution from personal errors or electrical faults.

In theory, a ground rod makes contact with perpetually wet or moist earth, providing a low impediance path for current to return to source. I don't know the spec for ground rod length for Thailand, but in the US it was eight feet. But it depends on where you are, a relatively wet area or bone dry (part of the year) Issan Driving a longer ground rod would increase the chances of your breakers tripping when needed. But it won't solve your stray voltge (N-E) problem.

If you are ever bored, with nothing more important to do you might get some water, the dirtier the better, and poor it around your ground rod

[Crossy]

Everyone needs to read this thread http://www.thaivisa.com/forum/topic/642020-do-we-really-need-ground-in-thailand/

An RCD / RCBO will NOT prevent you from receiving a shock if you grab a live wire, what it WILL do is reduce the possibility of you dying from that shock by opening the circuit in double quick time.

Whether you actually feel the shock or not depends upon many factors. Shoes and dry floor - probably not, no shoes and a wet floor - you'll likely know you've touched something bitey before the breaker opens. Either way the current is passing through YOU on its way to ground.

EDIT Lancelot, ground rod requirement here is 1.5m, about 8 feet

[gdhm]

Thanks for the link Crossy.

Dave

Edited June 21, 2013 by gdhm

[bankruatsteve]

Just to clarify the zap I got from a live neutral: I've been zapped many times (usually due to my haste or being lazy) and it was definitely the same as getting zapped by a normal live (well, it would be b/c N was then the live). Anyway, that did NOT trip the RCBO. Later and with correct polarity, I tested by putting one end of a wire in the dirt and touched the other to a MCB (live) screw and the RCBO tripped immediately. Maybe someone knows why it didn't trip when the N was live?

BTW: I was wearing "floppies" and VERY humid. So, I was probably a decent ground - and obviously not insulated.

Edited June 21, 2013 by bankruatsteve

[Lancelot]

Just to clarify the zap I got from a live neutral: I've been zapped many times (usually due to my haste or being lazy) and it was definitely the same as getting zapped by a normal live (well, it would be b/c N was then the live). Anyway, that did NOT trip the RCBO. Later and with correct polarity, I tested by putting one end of a wire in the dirt and touched the other to a MCB (live) screw and the RCBO tripped immediately. Maybe someone knows why it didn't trip when the N was live?

BTW: I was wearing "floppies" and VERY humid. So, I was probably a decent ground - and obviously not insulated.

I'll take a stab at this but will bow to Crossy's knowledge. Crossy, please correct me if I'm wrong

In theory the device should work, even with a reversed polarity because a RCBO measures the current (amperage) unbalance between the L and N conductors. I suspect that while you felt an electrical shock (tasted copper for 1 month as we say in the US) your flip flops gave you just enough insulation to limit the current through your body from reaching the device's trip current. When you performed your test, there were no flip flops between the live wire and Mother earth, so you had a low impedience path to ground and sufficient fault current to trip the device.

What is really dangerous about reversed polarity at the main breaker is that the branch circuit breaker would be open, but the "neutral" would still be live. I think in your example you were talking about reversed branch circuit polarity? Just throwing another example in

Edited June 22, 2013 by Lancelot