Help urgently needed please - RCB tripping with ONLY mains line/neutral connected

[cliveshep]

My brain isn't working. Apologies for a long-winded story here - please bear with me. And please don't suggest we find a competent electrician because there simply is no money, ill health in family members plus problems back in the UK have taken everything including 40,000 of my 400,000 which I need to scrimp for to replace by December. In a word - we are skint! Not asking for money - but a tech observation on the function of an RCB.

 

Our old house has been subjected to the usual Thai wiring over the years - twist and tape. When we bought the house I added a kitchen extension and a UK type ring-main on a 32a breaker, and also added 5 AC units. The extra lights I added were minimal loads, but of course a ring-main feeding a modern kitchen with a few electrical items and a washing machine from the UK meant the old breaker box was too small (I since put that in the workshop) Our builder is a complete cowboy it seems, he quite airily said he'd change the breaker box for one with more ways and as there is no way of isolating the incoming pair from the street outside I thought better you than me and let him do it.

 

Which he did, and instead of a 4-way box we now have a 12-way giving me outlets for air-con units, a workshop supply, and the new kitchen ring main,  and allowing the breakup of existing lighting circuits into groups so one breaker doesn't shut off all the lights and sockets. But most of the old wiring and the incoming mains cables that look to be about 25mm2 are all tightly jammed down a piece of  50cm length of buried 20mm plastic conduit between the box and the ceiling void.

 

Clearly the muppet had pulled hard on the wires because at least one red single has had the insulation cut against the top edge of the conduit just above the ceiling and the exposed wire is "live". Not sure where it goes except upstairs - will sort that later but he then compounded the error. Not only has he pulled all the slack out of the existing in a futile effort to connect it but the fool told me it had been wired up wrongly and he had done it "right". Right means connecting all the blues and blacks to the "fuse" ways and all the reds and browns to the neutral bus but cutting the new wires to suit - so a confused aircon engineer walked off the job saying it was dangerous and refusing to connect the air-con units.

 

So I laboriously took everything out and reconnected, joining the now too short wires with my ratchet crimper and insulated crimps and extra bits of wire and connecting into the breakers and neutral bus correctly. I also re-wired every outside condenser unit correctly and the air-con engineer came back and connected and was happy.

 

But my workshop had "live" earths so all the machines were "live" solved at the time by installing a decent 2m earth rod (the builder put a 60cm one into the sand fill outside, it did nothing.) in each corner of the house down into nice wet mud. I cross-bonded the lot creating what I believe they call an "equipotential enclosure". No more using rubber gloves on the bench grinder or pillar drill and touching metal objects didn't light up the neon!

 

And the RCB set for a while but then tripped and I put plastic spacers behind the breaker-box because I figured the builder had also trapped and pinched the old wires. Everything fine then for the last 5 years with no tripping and no earth problems. Subsequently built another extension and cross-bonded the steel frame to that.

 

But a few days ago the RCB tripped and would not reset. As it did this at 6.30pm it didn't give us much time to sort the problem out and at 38c I was in danger of electrocution I was literally running with sweat. Shutting down every one of the breakers and the RCB still would not set. So I took it out of the box, and tried to set it with only the live pair from outside in it, meaning it dangled on the mains cables. Still would not set. So we drove to Thai Watsadu who were still open and paid just under 3000 baht for a new one, came home and fitted it in hope.

 

Forlorn hope - won't set so I wasted money I simply cannot afford.

 

So I did a temporary bodge, wired in a couple of lengths of 2.5mm single into each side of the RCB along with the mains cables, the neutral side I connected into the neutral bus, and the live side into a spare 32A rcd. Then I did NOT turn on the RCB but left it off using it only as a glorified connector block and instead turned on the spare rcd feeding power into the live bus through that. So the lights and fans came back on, the two freezers started up - by then they had been off for 4 hours, and we had air-con in our bedroom at night.

 

So - we are going to break out the wall and cut the plastic conduit away and put heat-shrink over the damaged conductors. That is the cheapest option to leaving it on reduced loads with no Safe-T-Cut protection which I don't want to do. I'm old, my wife of 10 years a good bit younger, I don't want to leave her with more problems 

if I die.

 

Question after this "book" is - if a RCB device (main switch) wont set when dangling on only the live and neutral from outside - is it likely to be a neutral fault? i.e a cut in the insulation giving leakage? Like most 2-storey houses here the incoming pair come in under the eaves from the outside across the road, dive across the roof void which is not constructed to allow a person to walk over it, and down the wall in a tube to ground floor. It is not practical to access elsewhere!

[Nojohndoe]

If you have not tried this I would suggest flipping off ALL the relays on the board and seeing if the main will reset. If it does one by one reset distribution relays. Is it possible the supply meter has fried? I have seen that twice .

[carlyai]

Can you take a sensitive current reading on the incoming active and neutral wires to the RCB and see if they are the same?

[Crossy]

40 minutes ago, cliveshep said:

Question after this "book" is - if a RCB device (main switch) wont set when dangling on only the live and neutral from outside - is it likely to be a neutral fault?

 

If it really only has the incoming L&N and NOTHING on the outgoing side and won't stay on - It's almost certainly busted!

 

Check the "Test" button isn't stuck in!

 

Post a photo so we can see what's occuring.

[cliveshep]

Nojohndoe - done that already, as I said I even removed the RCB from the board completely and just connected the line and neutral to it so nothing else on it and it would not set. I now got 2 and both are doing the same thing - not touching anything only the two incoming connected.

 

Carlyai - I got a very expensive all-singing all-dancing UNI-T clamp meter and I know -only how to measure DC and AC voltage and continuity with it. That's all I needed if I was only installing a ring main or lighting circuit. This needs knowledge I probably don't have. I measured voltage live to neutral and live to earth - 227 and 224 respectively, tells me nothing haha. You might say "all the gear no idea" reasonably.

 

 

[carlyai]

7 minutes ago, Crossy said:

 

If it really only has the incoming L&N and NOTHING on the outgoing side and won't stay on - It's almost certainly busted!

 

Check the "Test" button isn't stuck in!

 

Post a photo so we can see what's occuring.

Thought he already changed the RCB before.

[cliveshep]

5 minutes ago, Crossy said:

 

If it really only has the incoming L&N and NOTHING on the outgoing side and won't stay on - It's almost certainly busted!

 

Check the "Test" button isn't stuck in!

 

Post a photo so we can see what's occuring.

Right now using a heat gun - carefully - to soften and cut and peel away the plastic conduit from a bunch of live wires. 

 

I got one RCB that was fine until 2 days ago, and one brand new one Crossy and both do the same. Right now I don't want to do the "dangling bit" because I need the power on to light (it's a bit dark as it's in a little passageway) and run the freezers.

 

I'll try and do some pics.

 

[Crossy]

OK, so it's not dangling and is a new unit.

 

With all your outgoing breakers OFF it won't stay on - correct? 

 

If that is the case then there's a strong possibilty that you do have a N-E fault.

 

Can you try measuring resistance (power OFF) between N and your earth? If it's a nice solid fault it will be easier to find.

 

EDIT What's the lowest current range on your clamp meter?

[cliveshep]

Got 3 ranges on the rotary switch - 20, 200 and 600 amp. But I got no idea how to use the clamp bit without spending a few hours reading the manual - never did 'cos all I wanted was continuity and voltage and those for the lorry actually!

 

Again - mains voltage across the RCN terminals 227v, line to earth 224v, neutral to earth gave 5.26 volt. Given 4 x 2m copper rods driven down one in each corner outside and all in wet mud I'd hazard a guess a neutral earth fault is right but why a voltage across the two? I'm not in any way anything other than a gifted amateur in basic electrics. 

 

Pics of the mess, the yellow bits are heat-shrink crimp connectors, I fitted those with a proper ratchet crimper not one of those silly crimp pliers that come in kits that practically cut the crimps in two! They were where I had to extend wires where my stupid builder had cut them short, putting the blues into the breakers and the browns/reds into the neutral bus, so everything in the house became switched on the neutral - dangerous when changing light bulbs as off on the wall switch left things still live.

 

You can see the wires going into the conduit I have broken out of the wall and am currently heating and cutting away to reveal damaged conductors hopefully including the incoming neutral!

 

Edit - you can also see the two bits of 2.5mm I am using to jump power into the box via the neutral bus and a spare 32a breaker

Edited July 7, 2021 by cliveshep

[Crossy]

Ouch!!!

 

PLEASE be very careful mucking about in there live!!!

 

[cliveshep]

Trust me - I am careful, all tools insulated and I have refrained from peeing on the live wires lol.

 

I've softened and cut away the conduit, I'm now about to track down and remove all damaged conductors and sleeve the damage with heat shrink. If the line appears damaged I'll wrap that in electrical tape and put a zip tie on the end to stop it unravelling in the heat. The neutral of course is safe once out of the box and I'll sleeve that with heat-shrink if I find damage.

 

My worry is that I will NOT find any damage meaning the problem might be in an inaccessible region where the idiot may have chafed it pulling too hard 5 years ago. What I can now do is lift the entire kit and caboodle up 3 or 4 inches now the conduit is no longer a limiting factor, the AC trunking I used can simply be cut shorter to allow things to go up. 

 

Then very minute inspection of all conductors above the ceiling! If that doesn't work then I don't know what i can do!

 

[carlyai]

Your meter has a clamp on the front..like a big claw...read up on how to measure 'current' (amps). You need to start measuring some currents.  ????

[MajorTom]

2 hours ago, cliveshep said:

Trust me - I am careful, all tools insulated and I have refrained from peeing on the live wires lol.

 

I've softened and cut away the conduit, I'm now about to track down and remove all damaged conductors and sleeve the damage with heat shrink. If the line appears damaged I'll wrap that in electrical tape and put a zip tie on the end to stop it unravelling in the heat. The neutral of course is safe once out of the box and I'll sleeve that with heat-shrink if I find damage.

 

My worry is that I will NOT find any damage meaning the problem might be in an inaccessible region where the idiot may have chafed it pulling too hard 5 years ago. What I can now do is lift the entire kit and caboodle up 3 or 4 inches now the conduit is no longer a limiting factor, the AC trunking I used can simply be cut shorter to allow things to go up. 

 

Then very minute inspection of all conductors above the ceiling! If that doesn't work then I don't know what i can do!

 

Hi,

First of all: Be careful assuming the "Neutral" is safe. Being an old house in Thailand i would assume you are supplied by an IT system. This does not have a neutral but actually two lives L1 and L2. But they usually call the L2=N and use blue wires. This does not mean its safe to touch..

 

The reason you have voltage between "N" and Earth is because its supposed to be there.

In normal circumstances and no earth faults you should have appx. 127V between Live and Earth and the same between "Neutral" and Earth. The reason its only 5.3V now is because there is an earthfault on the "Neutral" and thats probably also whats tripping the new RCB. (The dangling thing and connecting only supply side was only tested on the the old RCB??)

 

Try carefully disconnecting one by one "N" from the neutral bus and see if the RCB will stick. (remember to remove the bypass loop when you do this of course)

Edited July 7, 2021 by MajorTom
typo, duplicate

[Crossy]

@MajorTom I think it's much more likely to be TT than IT these days, a small N-E voltage would be quite normal then.

 

But your point about assuming N is safe is very well made, assume any wire is live until you prove that it isn't.

 

I wouldn't be working live it at all avoidable. A cheap "safety breaker" with the essential circuits on it bridged to the incoming supply would allow safe (dead) operations on the isolated CU whilst keeping the freezers and lights going.

 

[MajorTom]

24 minutes ago, Crossy said:

@MajorTom I think it's much more likely to be TT than IT these days, a small N-E voltage would be quite normal then.

 

But your point about assuming N is safe is very well made, assume any wire is live until you prove that it isn't.

 

I wouldn't be working live it at all avoidable. A cheap "safety breaker" with the essential circuits on it bridged to the incoming supply would allow safe (dead) operations on the isolated CU whilst keeping the freezers and lights going.

 

Yes you are correct. its TT. No one would use a neutral bus and single pole MCBs on a IT system. I hope...

[Crossy]

17 minutes ago, MajorTom said:

Yes you are correct. its TT. No one would use a neutral bus and single pole MCBs on a IT system. I hope...

Remember where we are!

 

There was at least one member in the past who had, what at least appeared to be, an IT system with the N bus waving around near half supply. I suspect it was actually a TT system with a missing or corroded star-point ground at the Tx (jungle village location), we never really got to the bottom of it.

 

Thailand is generally TNC-S, 3-phase, 4-wire with 220V P-N (230V in Bangkok under MEA) employing MEN (Multiple Earthed Neutral) with the neutral earthed at every 3rd pole or so, as well as in the CU where there is a N-E link (before any RCD/RCBO). If the neutral gets more than a volt or so above ground someone has a problem.

 

[cliveshep]

Got that Crossy - I think what you are all talking about is what they call PME in the UK, where the earth is bonded to the neutral at the head in the home or office and they rely on Positive Multiple Earthing creating an "equipotential" enclosure in the building where absolutely everything metal has to be cross-bonded to earth, metal taps if you only got plastic plumbing like Hep2o, your sink top and mixer taps, gas pipes, metal conduits, structural steels, and so on.

 

Why should there be 127 volts on the neutral? I got 227 across live neutral and 224 live-earth. the PD earth/neutral as said is 5.7 volts, interestingly a jumper earth/neutral gives little crackling sparks if one anchors one end say on the earth and strokes the other end on the neutral. I'm well aware that a break in the neutral on a live circuit will cause the neutral to be live as the current got nowhere to go. But this neutral is effectively dead to touch on it's own.

 

Major Tom - I did the "dangly thing" on both RCB's with the same result. 

 

The RCB is double pole of course. I'm thinking to open the roof over where the cables enter, and cut the cables, strip ends and shove them into a 100A joint box (got the big insulated cutters for outside cables from the UK for that) and run a new pair of 25mm cables down to the box and connect them in. I'll abandon the suspect ones altogether. If that doesn't solve the problem then it'll be the Bangkok Electricity company with the neutral problem and they'll need to solve it. 

 

However, I've gone as far as I can at the moment and we have a proper electrical company coming tomorrow so I can demonstrate what I have done and found, stop them wasting my time and lots of money frigging about testing the house after showing the "dangly thing" trick and see what they say and how much they'll charge to change the incoming pair. If it's multiple thousands then I'll have to do it as we simply cannot afford that kind of bill.

 

[MajorTom]

56 minutes ago, cliveshep said:

 

 

Why should there be 127 volts on the neutral?

 

 

Disregard that. Thats only relevant to IT supply which has a "floating" GND and no Neutral. Thats not what you have.

[Crossy]

9 hours ago, cliveshep said:

Major Tom - I did the "dangly thing" on both RCB's with the same result. 

Are you saying that with the RCBO unplugged from the board it won't stay on? 

 

That very strongly suggests that it's busted, but it's most odd that a new unit does it too.

 

By the way, DO NOT start cutting your incoming cables live, arc-flash can be very nasty (severe burns, blindness, death) if you want to splice in new stuff pull the live at least at the meter, most are not sealed and even if it is nobody cares.

[cliveshep]

"Crossy: Are you saying that with the RCBO unplugged from the board it won't stay on? "

 

Got it in one, that is EXACTLY what~ I'm saying. 

 

If everything turned off so no load on the incoming feed then no arc-flash. Remember, I've already pulled the incoming live off of the RCB to swap RCB's over (and I did that carefully including stripping back insulation and cutting a few mm off the copper wires and re-twisting to connect them again.

 

I long-ago bought tools that are insulated if only because more comfortable to use.

 

Just been up to my roof space with a torch, the incoming cables must have a good 20 feet of slack looping all over the top of the suspended ceiling so really all I need to do is get rid of the bit down the wall if that is what the electrician says. So that'll save a few thousand on new cables.

 

But already thought about how to do that as they wont move in the conduit although perhaps one in the roof pushing and one below pulling might bring them down but otherwise I'll run a new conduit down the wall behind the bedroom door and through the floor as that position is right above the breaker box.

[cliveshep]

Be interesting if the electrician says the new RCB is faulty too!

[MajorTom]

2 hours ago, cliveshep said:

Be interesting if the electrician says the new RCB is faulty too!

Connect a cable with a plug on the end and go test it in a socket outlet somewhere else.

[MajorTom]

3 hours ago, cliveshep said:

 

If everything turned off so no load on the incoming feed then no arc-flash.

It sounds like you know what you are doing, but be very careful. There will certainly be arc-flash if Live and Neutral come together somehow. Load or not. Normally you would have a face shield, fire protective clothes, ear protection etc. when doing this stuff. If that 25mm2 supply is shorted its not something you walk away from uninjured.

[Crossy]

7 minutes ago, MajorTom said:

It sounds like you know what you are doing, but be very careful. There will certainly be arc-flash if Live and Neutral come together somehow. Load or not. Normally you would have a face shield, fire protective clothes, ear protection etc. when doing this stuff. If that 25mm2 supply is shorted its not something you walk away from uninjured.

Indeed (or if it touches the grounded ceiling structure).

It's the work of a few moments to pull the live at the meter.

I'm certainly not going to be stripping and preparing a live end whilst up in my roof space. If it absolutely has to be live (it rarely does) then get a local to do it.

[Crossy]

33 minutes ago, MajorTom said:

Connect a cable with a plug on the end and go test it in a socket outlet somewhere else.

Why didn't I think of that? ????

 

[Crossy]

3 hours ago, cliveshep said:

Be interesting if the electrician says the new RCB is faulty too!

I can't think of any scenario where an upstream fault would cause an RCBO not to stay on.

 

Most odd.

[carlyai]

Just a question; if the new RCB without any load wires is tripping, why not use a clamp meter and read the current incoming on the active and then neutral cables?

Just a question and don't know why you don't want to do this.

 

[Crossy]

2 minutes ago, carlyai said:

Just a question; if the new RCB without any load wires is tripping, why not use a clamp meter and read the current incoming on the active and then neutral cables?

Just a question and don't know why you don't want to do this.

Not sure what it would prove, his meter isn't sensitive enough to measure a differential in the RCBO trip range and where would any differential come from if it's waving around in the air?

[MajorTom]

Just now, Crossy said:

I can't think of any scenario where an upstream fault would cause an RCBO not to stay on.

 

Most odd.

Yeah i thought residual current devices were uni-directional.. After reading up about it it sounds like a fault on the supply network or at the neighbors could trip it in certain perfect conditions. So can voltage drops or surges of course.

But the fact that it wont even turn on without any load connected sounds very strange.

[carlyai]

4 minutes ago, Crossy said:

Not sure what it would prove, his meter isn't sensitive enough to measure a differential in the RCBO trip range and where would any differential come from if it's waving around in the air?

Yep OK, was thinking a high resistance joint or something on the neutral, probably wrong thinking. Thanks.