I'm going to try all these suggestions on Monday and will report back with the results. Thanks so far.....

Does the RCBO trip if all the other breakers are OFF??

Just to follow on... Your #14 RCBO should not trip with all other breakers off. Then, one by one, turn on the other breakers until it trips. That is potential circuit shared. Turn off that breaker, reset RCBO and continue testing the rest of the breakers. There will need to be like fan or light turned in the circuit being tested.

Also, too late to edit my earlier post, but if you try that (continuity test on the uninstalled A/C circuits, the A/C breakers will need to be OFF for the continuity test)

Just tried your suggestions:

The #14 RCBO trips with all other breakers off except main RCBO.

Turned off main breaker and for the first time the #14 will allow itself to be reset. Turn on main and #14 trips.

So to recap. The #14 will not allow itself to be reset even when all other breakers are in the off position and the main is on.

OK, we need to go deeper.

First verify that you do have the RCBO wired correctly.

Disconnect all the other neutrals from the neutral bar (insulate the ends).

Does the RCBO stay on? If so does the circuit it controls work (plug in a light)?

I wanted to include the latest photo of the CU. I also wanted to tell you that I bought two of the new RCBO's, I have a meter and a plug in circuit tester I bought from the MEA in Bangkok.

Latest CU photo

Did I connect the RCBO correctly?

The black hot wire is removed from breaker #3 and attached to L of new RCBO

The black wire wouldn't be the problem. As Crossy said, you need to make sure you have the correct neutral for the circuit. That it trips with no other breaker on indicates that you do not have the correct neutral connected to the RCBO.

The black wire wouldn't be the problem. As Crossy said, you need to make sure you have the correct neutral for the circuit. That it trips with no other breaker on indicates that you do not have the correct neutral connected to the RCBO.

Yes I understand. I was just pointing out that I move the black wire to the new breaker. But how should I proceed to find the neutral? Thanks everyone for your assistance.

Power off.

All breakers off.

Short live and neutral at a point you know is controlled by the RCBO.

Use the meter to find the neutral(s) that are now connected to the live. Those neutrals should go to the RCBO.

Whilst you're at it check no other lives are joined to the one in the RCBO.

Correct the wiring.

Remove the short.

Check you've removed the short.

Power on.

Does it work properly now?

Status report:

I shut off all breakers.

I placed a short between live and neutral in an outside outlet.

I measured first between the hot black wire on RCBO #14 and all the other L on all other breakers. I found a short to breaker #1. I removed the wires (two white one red) from #1 and measured them one at a time. The red wire was shorted to #14 black L. I moved the red wire and added it to the RCBO breaker #14 L. None of the other L on the breakers measured a direct short.

I measured from the #14 L to the neutral bar and measured a short.

I removed the white wires from the neutral bar one at a time and measured between that wire and the #14. I found two white wires shorted so I moved both to the #14 N.

I checked continuity from the #14 L and the white wire that was "already" in the #14 N and found no short so I moved it to the neutral bar.

Removed short from outlet.

All breakers on. Only #14 trips.

I need to go back and remeasure everything because I was rushed at the end by tradesmen that needed power.

I know I made one mistake for sure.

Originally there were two whites and a red wire in breaker #1. I moved the red to #14 because it measured shorted to the black wire in #14.

I put one of the white wires back into breaker #1. I accidentally attached the other white wire to the neutral bar. (Lost track of my white wires)

Strangely enough none of the other breakers have tripped??????

During the tradesmen's break I returned the white wire I accidentally removed from breaker #1 back to breaker #1. I now find my downstairs lights work correctly

I also measured continuity across L and N on the RCBO breaker #14 while in the off position.....which I realize is actually #13 in the CU.

I measure a short!

So, the shorted outside outlet for testing has the short removed, yah?

The added piece to the puzzle is why a L from #1 would be connected to a L from (originally) #3. Just doesn't make sense.

Suggest you re-do the continuity tests and place a label on all wires that are connected just so you don't get mixed up.

You should also test for continuity between the neutral wires and the ground bar - hopefully none. But, there is no good reason your L and N should show continuity (or do you have something plugged into outlet on the RCBO circuit?)

Starting to become a brain teaser.

OK so I'm really confused. Unfortunately the electrician stopped by the house to replace a couple of light bulbs and reseat a starter and he offered no help other than to say that he was only the LAST electrician to work on this house and he can't tell me why things ate the way they are. Only that he got it all to work. He left quickly.

I decided to begin at the beginning and have placed all the wires back to where they were.

I needed some electricity!

To add to the fun you may also have a N-E fault (or deliberate connection).

Disconnect everything in the CU. Turn off all light switches and unplug all appliances. You should find NO connections between any wires in the CU.

Any connection indicates a fault.

Yeah. Unless you have the ways and means to trace all the wiring, you might end up going nuts trying to get things proper. If you have (or can borrow) an ammeter, you could check current flow on the neutrals with things loaded up just to see if you have need to worry.

Did you have any particular reason you wanted to use individual circuit RCBO when the main is RCBO? Unless the main RCD should happen to fail, there is nothing really added doing that. (Except to find shared circuits. )

Yeah. Unless you have the ways and means to trace all the wiring, you might end up going nuts trying to get things proper. If you have (or can borrow) an ammeter, you could check current flow on the neutrals with things loaded up just to see if you have need to worry.

Did you have any particular reason you wanted to use individual circuit RCBO when the main is RCBO? Unless the main RCD should happen to fail, there is nothing really added doing that. (Except to find shared circuits. )

The original intent was I wanted to isolate and protect the outside outlets. Eventually water/bugs will get in and I'll lose my main power. Most of the outside outlets are on breaker #3 which is for all outlets on the first floor.

I'm not going to give up yet. I'll try again in the morning.

Yeah. Unless you have the ways and means to trace all the wiring, you might end up going nuts trying to get things proper. If you have (or can borrow) an ammeter, you could check current flow on the neutrals with things loaded up just to see if you have need to worry.

Did you have any particular reason you wanted to use individual circuit RCBO when the main is RCBO? Unless the main RCD should happen to fail, there is nothing really added doing that. (Except to find shared circuits. )

The original intent was I wanted to isolate and protect the outside outlets. Eventually water/bugs will get in and I'll lose my main power. Most of the outside outlets are on breaker #3 which is for all outlets on the first floor.

I'm not going to give up yet. I'll try again in the morning.

Sounds good. Let us know how things turn out. You don't need individual RCBO to "protect" more than the main RCBO. If you want to isolate, a separate MCD will do it. Well, unless you already bought it and need to use it.