My CU

[Mike45]

The house is finishing up. The CU is completed.

The story is that the house was Wired by one set of electricians and now completed by a different group of electricians.

I bought that plugin checker device from the MEA and have tested every outlet. Found many with live and neutral reversed and some with a missing ground. The electrician has fixed all of them. They all pass test.

They found my "lost" RCBO MCB and have installed it and it hasn't tripped. I haven't tried the test button.

Breaker

#1 first floor lights

#2 second floor lights

# 3 first floor outlets

#4 second floor outlets

#5 oven, hood, cook top

#6,7,8 first floor AC units( not installed yet)

#9,10,11 second floor AC units( not installed yet)

#12 outdoor motion detector lights

Comments, suggestions, observations are welcome.

[Crossy]

Try the button

If you have outdoor lights or outlets put them on their own breakers so the RCD doesn't trip when the wet gets in (it will)

[IMHO]

My only observation is #5 - do you know what size cable you have on this circuit? An electric oven can chew up to 3kw on it's own, and electric cooktops can chew way more, if there's more than one hotplate turned on.

Just the oven and one big electric hotplate on could be at 6000 watts+ load already.

[IMHO]

If you have outdoor lights or outlets put them on their own breakers so the RCD doesn't trip when the wet gets in (it will)

+1. No matter what you do, moisture will get in and you will end up with RCD's tripping. On these circuits, use a breaker with it's own 10mA RCD in it, so it trips before your main (30mA) RCD does.

[Langsuan Man]

What is a CU ?

[Crossy]

What is a CU ?

Consumer Unit, Britspeak for load center, distribution board etc etc.

[Mike45]

My only observation is #5 - do you know what size cable you have on this circuit? An electric oven can chew up to 3kw on it's own, and electric cooktops can chew way more, if there's more than one hotplate turned on.

Just the oven and one big electric hotplate on could be at 6000 watts+ load already.

The oven is electric but the cook top is gas. What size wire should I have for just the oven?

[bankruatsteve]

Depends on how much amps/watts the oven draws. Most ovens I have seen here draw less than 20a so 2.5mm2 should be good.

[Mike45]

If you have outdoor lights or outlets put them on their own breakers so the RCD doesn't trip when the wet gets in (it will)

+1. No matter what you do, moisture will get in and you will end up with RCD's tripping. On these circuits, use a breaker with it's own 10mA RCD in it, so it trips before your main (30mA) RCD does.

I know there are outlets on the first and second floors externally. Also lights on the first floor externally.

The way he setup the CU it means that the first floor lights breaker and the first and second floor outlets breakers will have to be replaced.

Correct?

[IMHO]

My only observation is #5 - do you know what size cable you have on this circuit? An electric oven can chew up to 3kw on it's own, and electric cooktops can chew way more, if there's more than one hotplate turned on.

Just the oven and one big electric hotplate on could be at 6000 watts+ load already.

The oven is electric but the cook top is gas. What size wire should I have for just the oven?

OK, that changes it a lot - not sure why cooktop was included on the label

As Stave says, 2.5mm2 is usually enough - unless you have one of the big 90cm / 120cm wide ovens?

[IMHO]

If you have outdoor lights or outlets put them on their own breakers so the RCD doesn't trip when the wet gets in (it will)

+1. No matter what you do, moisture will get in and you will end up with RCD's tripping. On these circuits, use a breaker with it's own 10mA RCD in it, so it trips before your main (30mA) RCD does.

I know there are outlets on the first and second floors externally. Also lights on the first floor externally.

The way he setup the CU it means that the first floor lights breaker and the first and second floor outlets breakers will have to be replaced.

Correct?

It sounds like it, yes. We use ones like this for external light circuits:

[Mike45]

The house is finishing up. The CU is completed.

The story is that the house was Wired by one set of electricians and now completed by a different group of electricians.

I bought that plugin checker device from the MEA and have tested every outlet. Found many with live and neutral reversed and some with a missing ground. The electrician has fixed all of them. They all pass test.

They found my "lost" RCBO MCB and have installed it and it hasn't tripped. I haven't tried the test button.

Breaker

#1 first floor lights

#2 second floor lights

# 3 first floor outlets

#4 second floor outlets

#5 oven, hood, cook top

#6,7,8 first floor AC units( not installed yet)

#9,10,11 second floor AC units( not installed yet)

#12 outdoor motion detector lights

Comments, suggestions, observations are welcome.

Sorry. I thought I had attached this photo to my Original Post

[IMHO]

The house is finishing up. The CU is completed.

The story is that the house was Wired by one set of electricians and now completed by a different group of electricians.

I bought that plugin checker device from the MEA and have tested every outlet. Found many with live and neutral reversed and some with a missing ground. The electrician has fixed all of them. They all pass test.

They found my "lost" RCBO MCB and have installed it and it hasn't tripped. I haven't tried the test button.

Breaker

#1 first floor lights

#2 second floor lights

# 3 first floor outlets

#4 second floor outlets

#5 oven, hood, cook top

#6,7,8 first floor AC units( not installed yet)

#9,10,11 second floor AC units( not installed yet)

#12 outdoor motion detector lights

Comments, suggestions, observations are welcome.

Sorry. I thought I had attached this photo to my Original Post

That's a helluva ground rod wire

[Crossy]

What's with the darker coloured wire on the 3rd breaker, looks a bit odd?

[IMHO]

What's with the darker coloured wire on the 3rd breaker, looks a bit odd?

If you're going to bring that up, what's the deal with the 3 white wires on the active side? Everywhere else it's clear they've used white as neutral. There's also 3 unterminated red wires...

[Crossy]

What's with the darker coloured wire on the 3rd breaker, looks a bit odd?

If you're going to bring that up, what's the deal with the 3 white wires on the active side? Everywhere else it's clear they've used white as neutral. There's also 3 unterminated red wires...

I detect a few borrowed neutrals in there too, there should be the same number of neutrals as lives.

If our OP wants to add individual RCBOs to some circuits fun will ensue.

[Mike45]

What's with the darker coloured wire on the 3rd breaker, looks a bit odd?

If you're going to bring that up, what's the deal with the 3 white wires on the active side? Everywhere else it's clear they've used white as neutral. There's also 3 unterminated red wires...

I detect a few borrowed neutrals in there too, there should be the same number of neutrals as lives.

If our OP wants to add individual RCBOs to some circuits fun will ensue.

Sounds like this is going to be fun to frustrating to impossible to accomplished.

I was going to try to identify the circuits by disconnecting then reconnecting one by one the three wires on the third breaker (first floor outlets circuit) then add another breaker as s recommended.

But this borrowed neutral thing sounds a lot more complicated.

Is it possible I won't be able to accomplish adding the individual protected breakers because of the missing neutrals?

How do you recommend I proceed? Plan of attack?

[Mike45]

If I had to guess I would say that the black wire on the third breaker probably went to the outside additional room that has most, but not all, outside outlets and lights. I believe my builder subbed out that project. The sub probably used a different wiring convention.

[wayned]

What is a CU ?

Consumer Unit, Britspeak for load center, distribution board etc etc.

I'm American. We call it either a fuse box or circuit breaker box. One has fuses in it, the orher circuit breakers! Makes sense.

My CU, consumer unit, is my wife. My load center is where I take a dump, the bathroom! Why make it difficult?

That said, Have a Happy New Year!

[IMHO]

My CU, consumer unit, is my wife.

Oh yeah? Wait until you have teenagers

[Mike45]

Is there an easy way to identify which return goes with which hot wire

[Crossy]

Probably the easiest (but not the safest) way is to remove each neutral in turn (with the power off) to see what stops working.

A better (and safer) way would be to use a bulb, battery and long wire to trace where each neutral ends up, then you can match it with its associated live.

[bankruatsteve]

The potential problem with borrowed neutral is over-current on the unprotected neutral. As noted, individual circuit RCBO just won't work if the circuit is shared. But, in this case, it seems unnecessary to install individual circuit RCBO since the main breaker is RCBO.

If the borrowed neutral is in the lighting circuits, maybe not to worry. Otherwise, it really should be sorted out.

[Mike45]

Before seeing the last two posters I went ahead and:

Connected my outlet tester to an outside outlet. It read OK.

In turn I shut off power and disconnected one return wire then turned on power. Each time the tester read good. Never lost power to it. One time, on #9, I momentary saw a ground fault light come on the tester but then it went quickly away. The only time I lose power to the outlet is when I shut off breaker #3 first floor outlets.

[Crossy]

Try it with a regular light bulb L-N, but from what you are describing there is possibly a link between two neutrals somewhere.

Remove all the neutrals from the terminals (tape the ends for safety) and reconnect one at a time identifying what works with each neutral.

[bankruatsteve]

I wonder if the A/C circuits are sharing N? 3 up and 3 down. That would be the last type of circuit for someone to even consider sharing a neutral but it could explain the wire count difference.

If you have a meter, one way to check the A/C circuits is to put the meter on ohms scale and then:

Turn main breaker off. <------

Short each of the A/C circuits. (connect N to L at the end of the run)

Remove each N from the neutral bar in turn and check for continuity with each A/C breaker screw. If more than one, then N is shared. At least one should have continuity.

Disconnect shorts. <--------

[Mike45]

Next attempt: I opened one of the outlet boxes in the outside addition area. The line wire was black. So now I know that the mysterious black wire on breaker #3 is probably going to these outlets.

I separated the black wire from breaker #3 and installed the new Schneider RCBO into position #14.

I attached the black wire to it's L.

With this breaker on I now had power to the outside outlets. I continued by removing the neutrals on the neutral bar and when I got to position #4 the outside outlets lost power.

I attached that neutral wire to the new RCBO N position. I attached the blue wire from the RCBO to the neutral bar.

The breaker trips immediately after resetting.

????? How to continue?

[Mike45]

Sorry didn't see your two previous posts. I'll read them over carefully

[Crossy]

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

[bankruatsteve]

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)