A few questions about my electrical installation/ consumer unit

[Jurghh]

Hi All. I've been a lurker for a while, though never in this forum, but this is my first post. I hope to be able to contribute and help others in the future.

 

So here goes... I'm redoing the kitchen in my BKK condo and I want to add 4 new circuits (sockets & microwave, dishwasher, oven, water heater). The CU is located in the kitchen. I've already chased the walls and installed conduit & back boxes etc.

 

Initially I planned just to add standard MCBs like the ones currently installed but now as I've learnt a little bit more about electrics I think it's better if more or all circuits are RCD protected. Currently only circuit 6 (three down from the right, blue wire) is protected by an RCD. This is the circuit for the existing sockets in the kitchen. So i've got a few questions i'd be very grateful if anyone could help answer:

 

1. What would be the best way to add RCD protection given the layout of the 3 phase CU? To all circuits or is it less important for others? 

2. Could for example all of the existing MCBs be swapped out for 1P RCBOs? The Siemens ones have functional earth wires that need connecting. RCCBs an option?

3. Why did the installers use a 2P RCBO linked to an MCB to add RCD protection to the existing kitchen sockets instead of a single 1P RCBO?

4. Why did the installers break the colour pattern and use black wire instead of red for the bottom left L2 circuit?

All of the companies I've had round to do a survey and quotation haven't actually offered a solution in any detail.

 

 

[Crossy]

Looks like a nice installation to start with 🙂 

Is the ground bar actually linked to ground?

 

Those siemens MCBs seem to be normal DIN mount units rather than plug-in 🙂 

 

Single-width RCBOs that will fit are available, although not necessarily cheap. This is possibly why a separate RCD/RCBO was used for the kitchen. Do you have a part number for the Siemens units you found?

 

Sadly, it looks like you will have to extend the white neutral wires for the circuits you need to protect, but such is life.

 

Wire colours? "It's what was in the van guv"

 

I would decide which circuits you need to protect with RCBOs and then look at the costs. Certainly, I would do outside lighting and outlets, water heaters, kitchen outlets except for your fridge/freezer.

 

 

[Jurghh]

Thanks for the detailed reply. The ground bar goes into the wall with more heavy duty fixings than say the neutral bar. I loosened off the nut to see what kind of bolt's been used but the whole thing just kept spinning. That was the case for both nuts on the earth bar. There is continuity between the neutral and CPC wires at every receptacle that i've played around with and tested. There's also continuity between the ground bar and the neutral bar in the CU. 

 

You're right about the MCBs. They don't clip on to the rail like the RCBO below clips onto its rail. If the screw isn't tightened they won't hold on the rail. I've also noticed that the MCBs appear to fit a bit better the opposite way round (see new photo). There are no load or line markings on the MCBs so I think they can be used either way. 

 

Lazada link for the Siemens RCBO 5SU9. https://tinyurl.com/4ehvb246. These have line and load markings. I'm pretty sure they'll fit on the rail where the MCBs are. The bit that's confusing me is the blue neutral wire that they come with. Does that need to be attached at the CU? The MCBs only have a single cable (hot) going to each circuit.

 

Regarding the circuits to add RCD protection to, I've uploaded the CU wiring diagram. The fridge freezer is already on the circuit with the RCBO fitted.

 

 

[Jurghh]

After some more research I think i've found that all the MCBs can be changed to single width RCBOs. They fixed neutral wire attached to the RCBO is 60cm. That wire goes into the neutral bar and the neutrals from the load side (currently in the neutral bar) go into the top of the RCBOs. Those neutral wires will most likely need to be extended with inline Wagos.

 

Regarding the earth bar, i'm still confused by what's going on there. Could it be that the earth and neutral are connected somewhere before my consumer unit? 

[Crossy]

Earth and neutral are certainly linked somewhere in the installation.

 

In a condo it's likely that you have a TNC-S (or possibly TNS in an older place).

 

Have a look here https://en.wikipedia.org/wiki/Earthing_system

 

If you don't actually see a link then it's going to be elsewhere.

 

If you measure 220-230V between a live and the earth and something close to zero between neutral and earth you're likely good to go. In our old condo all the A/C units were supplied from live and earth!!! They worked just fine although I did move the connections to the right place 🙂 

[Jurghh]

11 hours ago, Crossy said:

Earth and neutral are certainly linked somewhere in the installation.

 

In a condo it's likely that you have a TNC-S (or possibly TNS in an older place).

 

Have a look here https://en.wikipedia.org/wiki/Earthing_system

 

If you don't actually see a link then it's going to be elsewhere.

 

If you measure 220-230V between a live and the earth and something close to zero between neutral and earth you're likely good to go. In our old condo all the A/C units were supplied from live and earth!!! They worked just fine although I did move the connections to the right place 🙂 

 

One of the senior technicians from my building came to have a look today. There was a language barrier but we managed to clear a few things up. They invited me into the main electrics room for the floor and showed me the main ground cables. There were 10 cables for the ten apartments (so I had one). He said it was not normal that the main ground cable from that room did not connect directly to the earth bar in my CU. I explained that I was confused because i've owned the place since new and the installation is original. Somewhere between that control room about 10 metres away and my CU the main earth cable is doing something mysterious. 

 

Nonetheless it would appear that the circuits are grounded. I tested 231V L to E and 0.45v N to E. They also said I should be fine to swap the MCBs for single width RCBOs. I'm going to order one RCBO first and see if it works. I've uploaded a photo from the control room. There are 10 green earth wires connected.

[Jurghh]

I think I know what might have happened. Looking at the photo the green wires look quite thin (similar to the thickest green wires in my CU). I should measure the diameter of one of those wires in the control room to see if it matches the thickest wire connected to my earth bar.

 

There are 11 white cables connected to the neutral bar for the 11 circuits installed plus the thick black cable at the top of the bar. There are also 11 green cables connected to the earth bar. The lighting circuit (all lights on one circuit) doesn't have an earth cable. So if the green cable diameters match (as explained above) then the earth bar likely is connected to the building's main earthing. 10 green cables for the circuits plus 1 out to the control room. What do you think?

 

[sometimewoodworker]

On 3/17/2025 at 8:25 PM, Jurghh said:

I'm going to order one RCBO first and see if it works.

You should test it in each circuit before buying too many. It is quite possible that you may have a borrowed neutral or 2. That can be very difficult to locate and will either instantly trip an RCBO or trip it when an appliance/light is turned on. For my house it took a competent electriction almost 5 hours of testing to find and eliminate the problem.

 

 

[Jurghh]

21 hours ago, sometimewoodworker said:

You should test it in each circuit before buying too many. It is quite possible that you may have a borrowed neutral or 2. That can be very difficult to locate and will either instantly trip an RCBO or trip it when an appliance/light is turned on. For my house it took a competent electriction almost 5 hours of testing to find and eliminate the problem.

 

 

 

That's a good point, thanks. The wiring looks pretty decent so far so i'm hoping they haven't connected any borrowed neutrals. 

[sometimewoodworker]

On 3/20/2025 at 10:23 AM, Jurghh said:

 

That's a good point, thanks. The wiring looks pretty decent so far so i'm hoping they haven't connected any borrowed neutrals. 

The wiring maybe in perfect condition and a borrowed neutral may only ever be a problem of you try to install an RCBO on a circuit that has one.

With whole house RCBO’s it is never a problem, just with individual circuit RCBO’s

 

[Jurghh]

I swapped a sockets circuit MCB with a 16A RCBO and it worked fine. I tested the RCD function with a socket tester and the circuit tripped like it's supposed to. I guess the next main thing to consider is balancing the load on the three different lines when adding the 4 new circuits. I've got the torque specs for the RCBO but I don't have anything for the neutral bar. The screws are quite soft and don't seem to like much more than 1.5nm. Is that sufficient?

[sometimewoodworker]

10 hours ago, Jurghh said:

I've got the torque specs for the RCBO but I don't have anything for the neutral bar. The screws are quite soft and don't seem to like much more than 1.5nm. Is that sufficient?

In over 60 years of doing electrical stuff I have never used a torque screwdriver, I have never had one of my connections come loose. The only connection that has ever needed to be tightened was one done by a non electrician in our house.

 

Just try tightening connections on a test socket using gorilla strength. There will be some possible outcomes 

with a slot headed screw you will break half of the head off

with a Philips screw you will round off the recess in the head

with any screw you will break off the screw under the head

with any screw you will strip the screw thread 

with any screw you will strip the threads it’s going into.

 

I have experienced all the above, most over 60 years ago

 

the outcomes are partly dependent on the quality of the screws and threaded section as well as your strength.

 

However once you have experienced some or all the above you will develop a feel as to when tight is tight enough.

 

NEVER use an impact driver or any power driver.