Some background first: I have a single-phase system (220V). I installed an RCBO direct from the external supply and then the output from that went into the main breaker panel outside the house. wiring direct to RCBO

I seem to have some leakage somewhere in the house, which kept tripping the RCBO. There's another RCBO built into the subpanel inside the house and that doesn't trip, so I went back to the installation of the new RCBO.

The manual says to wire the hot/live cable to the live RCBO input and the neutral cable must first go to the neutral block on the panel and then from there to the neutral RCBO input. Each subpanel has its own ground, so I only link the ground and neutral blocks on the main panel.

connecting RCBO via the neutral block

This alternative installation doesn't make sense to me, but if that's what the installation pamphlet says then I won't argue. The RCBO still trips - so that didn't solve that problem.

However, now I have a new problem. If I switch on one of the breakers, I get the normal 220V going through that breaker.


(It may be that this was the case beforehand and I just didn't notice. Could ALL the breakers be faulty? Or could it be some weird wiring with the main breaker that's the cause of it - maybe connecting the cables into the wrong ends?)

A related problem is that there's 220V going to ground when one of the breakers is on. I think that's normal. But the electrician has probably connected the earth to the pole carrying the cables from the grid. It's a metal pole sticking out of the ground - and registers 220V. Is that normal? Is that safe!???

I'm tearing my hair out. And I've called in 3 electricians already, but we live in Thailand where just about anybody can call themselves an electrician. They don't seem to know much more about installations (and RCBOs) than I do (which isn't all that much).

Any ideas? Please help!

  • 1
    Electrical terminology: A closed breaker would have full voltage going through it - an open one would not. Closed = on, open = off for switches and breakers.
    – Ecnerwal
    Mar 14, 2016 at 17:06

3 Answers 3


The 2-6 volts is not leakage, it's being induced - picked up like an antenna from adjacent conductors which are hot. You're only seeing it because your DVM is very sensitive. If you put any kind of load on it, even a night light, the voltage will disappear because there's no force behind it. I've built passive AM radios that work on this principle, the airwaves itself powering a very tiny, delicate earpiece, doesn't work with heavier headphones.

RCBO, we call them GFCI in America, because they detect "ground faults". They work like this.

enter image description here

In the drawing, tying the RCBO's incoming AND outgoing neutral to your panel is a complete fiasco, because it gives neutral current a path around the RCBO, which utterly defeats the purpose. Here is how that will trip unnecessarily.

enter image description here

The smaller RCBO in your diagram is "less wrong" but still problematic, as neutral can go down the ground tie to your neighbor's ground tie, into his panel and back to the transformer that way. Assuming you share a transformer. And even worse, the ground bus is tied to the neutral output of the RCBO, which means the RCBO can't see actual ground faults.

enter image description here

You should have TWO neutrals - the rough-and-tumble base neutral prior to the RCBO, and the protected neutral after the RCBO, which serves the exact same circuits as the RCBO hots with no exceptions. IE something like this. (note that chaining RCBOs like this is purposeless and I assume you're doing it because of the panels you are stuck with.) I shaded the protected area blue, note the ground is outside of it!

enter image description here

And of course, the safety ground is also run to every outlet - that is the third wire. The safety ground must be tied to neutral before the RCBO - if it is tied downstream of an RCBO, then the RCBO won't be aware of ground faults. Fault current must bypass the RBCO.

This thing looks odd, because we're mixing European and American paradigms... Thailand. Having a whole-house RBCO is a European concept. In America you use individual GFCI breakers on certain circuits and not others - as a result, a trip will not plunge you into darkness or leave you a fridge full of spoiled food.

And lastly, I suspect you have a ground fault somewhere in the house - perhaps that's why you hooked up the RCBOs wrong (in the drawing) - because if you hook them up right, they trip. Well, they're supposed to trip.

Seeing 220V on your ground line is not right, unless you are measuring improperly somehow. That indicates a condition that the breaker or RCBO should be tripping on.

  • Thank you Wolf, this makes a lot more sense than the instruction pamphlet that came with the RCBO/GFCI. Actually, there were similar wiring diagrams, but it wasn't clear that the panel depicted was a sub-panel (so should have no bonding). I'll add in a new, separate panel as the main panel, with just a large single breaker and the GFCI as per your excellent diagram. The subpanel inside the house is a combined unit with the main breaker also acting as a GFCI, rated at 15mA. There does seem to be a ground fault somewhere and I'm looking for it, but it's not tripping the integrated GFCI
    – Gary
    Mar 14, 2016 at 2:46
  • The voltage on ground might be because the ground is (and has been) bonded to neutral throughout the system. There's no current going to ground, but it's worrying. I even found 220V between live and a metal paint tin that was just sitting on the ground nearby!
    – Gary
    Mar 14, 2016 at 2:58
  • @Gary Glad it was helpful. By the way I just added 3 drawings on how GFCI's work. Did not know your RCBO's sensitivity was 15ma. Not sure if worth the work to revise drawings, more inclined to not worry about it. Mar 14, 2016 at 3:21
  • Wow, really amazing diagrams, thank you! The daddy GFCI can be set from 6mA to 30mA (I've set it to 30mA). The one built-in to the sub-panel is 15mA. I've rewired the panels and (so far) it's not tripping.
    – Gary
    Mar 14, 2016 at 5:42
  • Update. Rewired as follows i.stack.imgur.com/d62NB.jpg. But I'm still getting a voltage reading between live & ground. This is very curious. I'm getting 220V - no current - when measuring between live and the pole-in-the-ground. I'm also getting the same voltage when measuring between live and the panel box (without connecting this to ground)! I also checked the subpanel, which reads 220V to ground. But when I disconnected the ground block, I'm getting 100V when measuring between live and the panel box! When I measure between live and just a nail in the wall, I get about 20V. Ideas?
    – Gary
    Mar 14, 2016 at 5:45

2-6 volts into a high inductance meter may just be inductive hum picked up from nearby wires. Unless it can sustain considerable amperage, I wouldn't worry about it.


Okay, I think I've figured it out now. I was ignorant about the purpose of the neutral part of the circuit and how it relates to ground. Please correct me if I'm wrong:

The neutral line is the same as ground, but connected way down at the transformer. The live line is what provides the voltage "push".

So I should get the full 220V (what's left of the original 240V after resistance in the cable) between live and anything that is properly grounded.

potential difference between live and ground/neutral

The fact that I'm getting 100V between live and the ungrounded metal chassis via the screw in the wall means that there's still 120V of "push" left that can flow through some other grounded object (or person).

I know this isn't a scientifically-correct explanation, but I think a bear with little brain like me can undererstand it. If I've misunderstood it then please advise! :) Thanks.

PS Now the next part of my project is to figure out how to test/measure for leakage in the various circuits.... I suspect that there must still be leakage somewhere, especially as some of the cables are underground (which gets soaked when it rains) and the wire insulations aren't all necessarily waterproof I don't think.

  • Close. All grounds must be bonded to each other. In your drawing, "draw a heavy green line" between the two ground rods, you can't rely on a water pipe or the actual earth. Double ground rods aren't illegal but are redundant since you still must have wire between them. Mar 14, 2016 at 17:35
  • This 100V thing is really bugging me. I think it's your sensitive meter. Moot the point by positively bonding all electrical boxes to ground. I hope that's what the thin green line is. My rule is simple: Ground everything solidly, first... then fix the wiring problem. The goal is not to prevent trips, it's to fix the system. Focus on junctions, splices and appliances... insulation is quite good and long runs of wire (even wet) are unlikely to be the problem unless the insulation has taken physical damage somewhere. Water in a splice, on the other hand... Mar 14, 2016 at 18:07
  • It's unlikely you have 20V of loss in cable resistance. Probably the transformer is supplying 220 not 240. Here's a sure way to tell: turn off all your big electrical loads and measure voltage. Turn on all your big loads and measure voltage again. A big difference reveals cable losses. The precise math is Voltage drop = Amps flowed * Resistance of wire. Mar 14, 2016 at 18:38
  • Thanks, I'll do as you suggest. The transformer is 1/2 mile away and you are right, the supply is 220V (not 240V). I understand that the transformer has its own ground (right??) and obviously I can't bond the grounds between my house and that of the transformer. Finally, how does one bond grounds that are about 100m apart? (My "house" is actually a collection of large rooms on an open piece of land, like a resort.) The point of this exercise is to make sure everything is safe, that's why I installed an extra master GFCI in the first place - and when I realized that something's not right .
    – Gary
    Mar 15, 2016 at 5:25
  • Problem solved Thank you Wolf. I discovered that, at some point, I had switched the live & neutral wiring. In Thailand, the color code is grey and black, but there is a rainbow of other colors, red/white, even yellow. Green is usually for ground, but it can sometimes be black or even red! Traditionally black is live, so I wired up all the circuits in the house so that black is live and grey is neutral. Then when trying to find the leak and understand the voltage problems, I switched the wiring round at the panel a few times and ended up with grey on live and black on neutral!
    – Gary
    Mar 15, 2016 at 10:59

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.