Thoughts on new electrical system for townhouse with 3 floors

[Dwight]

Hi everyone,

 

I am renovating a smaller townhouse with 3 floors and are planning the new electrical system. The plan is to rent out 5 small rooms in the building so I would like each of these rooms to have their separate consumer unit with RCBO for all circuits and I am also planning to install a small kWh meter in each of these sub-consumer units. The rooms are small and will basically have a 9000BTU AC, 2-4 sockets and some downlights. 2 of the sub-units will also feed a shower heater each.

 

Here is a sketch of the setup I am planning for. May I please ask for your thoughts about this setup? Some questions I have is:

 

Is the 6mm2 THW feeder for the sub-units too small? Would I be better off splitting the 4 sub-units between 2 separate 6mm2 feeders?

Should the feeder(s) for the sub-units have their separate MCBs after the Main RCBO in the main consumer unit instead of being run straight off the main supply?

 

Very thankful for any input,

 

Best,

Dwight

[Crossy]

I would add a front-end 63A MCB (assuming a 15/45 meter) in a separate box that will kill all the power from one location and provide overload protection for your meter.

 

I would also run separate cables from the source to each of your secondary units. That would also allow you to meter each room from a central point and no risk of your users trying to bypass.

 

[bankruatsteve]

I don't know what the Thai regs are for MEN with multiple CU's, but it doesn't seem correct to me to have the neutral feeding from the ground bar after the main CU.  @Crossy?

 

Run single cables in the PVC and the ground can be downsized, IMO.

[Crossy]

5 minutes ago, bankruatsteve said:

I don't know what the Thai regs are for MEN with multiple CU's, but it doesn't seem correct to me to have the neutral feeding from the ground bar after the main CU.  @Crossy?

 

Run single cables in the PVC and the ground can be downsized, IMO.

 

Yeah, I think you're correct there. The N-E connection is fine but I'd be splitting the supply after my suggested "Overall" breaker and not rely on connecting inside the main CU.

 

A couple of the 125 or 160 versions of these in the box with the overall breaker would do the trick. You could make the N-E connection to one of those too.

 

https://www.aliexpress.com/item/32961240438.html

 

[Dwight]

Excellent, thank you very much for your input. Much appreciated! I will definitely install the main breaker in a separate enclosure and split the supply in that enclosure and also do the N-E connection there. However, let's say I was not concerned about having the meters placed in the secondary units and I really wanted to reduce the feeder cables having to be pulled from ground floor to maximum 1 feeder per floor. I could do this by installing 1 larger secondary unit per floor with 2 RCBOs and 2 kWh meters and then supply 2 rooms from there. What do you think? Would you say 3x6mm2 is enough or would you say go for 10mm2 per floor since it is fed from the 63A MCB?

 

Again, thank you very much for your help, really appreciate it! 

[Crossy]

18 hours ago, Dwight said:

Excellent, thank you very much for your input. Much appreciated! I will definitely install the main breaker in a separate enclosure and split the supply in that enclosure and also do the N-E connection there. However, let's say I was not concerned about having the meters placed in the secondary units and I really wanted to reduce the feeder cables having to be pulled from ground floor to maximum 1 feeder per floor. I could do this by installing 1 larger secondary unit per floor with 2 RCBOs and 2 kWh meters and then supply 2 rooms from there. What do you think? Would you say 3x6mm2 is enough or would you say go for 10mm2 per floor since it is fed from the 63A MCB?

 

Again, thank you very much for your help, really appreciate it! 

 

You need to ensure your sub-mains are protected from overload. The 63A main breaker would do that job ok if the subs were 10mm², 6mm² is generally rated at around 50A and would be too small.

 

Daisy chaining the rooms on 10mm² like your original diagram would be OK, but don't use the ground bar as the neutral link in those secondary units, take both L and N from the inlet side of the RCD.

 

Or if you have 2 rooms per floor run 10mm to the first room on floor 1, then daisy chain to the next room in 6mm**.

Feed 10mm to the next floor from the first roon on floor 1. Getting 2 x 10mm + 1 x 6mm into the feed side of the first RCBO would be a wrestle, best to use another pair of those terminal blocks I linked to.

 

There are many ways of doing this, once you've decided do another sketch and post for more comments ???? 

 

EDIT for clarity: ** the 6mm² is protected from overload by the 32A RCBO at the far end, the incoming 63A MCB provides short-circuit protection.

[easydoor]

One thing I don't agree with and ask myself why you did it:

you connect the N (neuter) with the earth.

KEEP the Bleu and the Green wires complete separated in the main box, just as you did in the secondary boxes !!!!

[bankruatsteve]

6 minutes ago, easydoor said:

One thing I don't agree with and ask myself why you did it:

you connect the N (neuter) with the earth.

KEEP the Bleu and the Green wires complete separated in the main box, just as you did in the secondary boxes !!!!

No.  The mains N connects to Earth bar in the main CU per Thai requirement for MEN.

[sometimewoodworker]

9 minutes ago, easydoor said:

One thing I don't agree with and ask myself why you did it:

you connect the N (neuter) with the earth.

KEEP the Bleu and the Green wires complete separated in the main box, just as you did in the secondary boxes !!!!

Because it’s required by the PEA if in a MEN area

you clearly don’t understand Thai or English wiring.

[Dwight]

First of all, thank you all for your input. And thank you @Crossy for clarifying regarding overload and short-circuit protection. I have sketched another solution based on your comments and based on some more discussions with the others that are involved in this project. Unfortunately I am not in a position where I can design the system exactly as I want it, but some compromises had to be made. Long story short, here are some important updates to my original post:

 

1. I will be able to run 1 supply cable to each floor but the cable area will have to be no more than 6mm2 (THW 3x6mm2)

2. I have calculated the max load for each floor to be around 35-40 amps, but it is very unlikely that this will ever be needed

3. It seems that MEN is not implemented in this area so while waiting for confirmation I have removed the N-PE connection from the drawing.

 

So here is my latest suggestion for the installation. Please note that for the ground floor I might put the RCBO and MCBs in a separate box and not together with the supply MCBs. I would have preferred to have individual 10mm2 to each floor and perhaps even to each individual sub-unit, but I am afraid this is as good as I can get it. What do you think?

 

TIA,

 

Dwight

 

 

[bankruatsteve]

I like it.  If the rooms won't have kitchens/appliances your max load per floor is probably 25A or less so the 6mm² should be good.  No meters?  No pumps?

[Dwight]

4 hours ago, bankruatsteve said:

I like it.  If the rooms won't have kitchens/appliances your max load per floor is probably 25A or less so the 6mm² should be good.  No meters?  No pumps?

 

Thanks! For meters there will be DIN-rail kWh meters fitted in the sub-units on floor 2 and 3. The ground floor has a kitchen area where the water pump is located and this will be supplied from the consumer unit on the ground floor. I will probably change my drawing a bit and move the RCBO and MCB:s needed for the ground floor out of the main consumer unit and put them in a separate box just to tidy it up a bit. 

[Crossy]

Yeah, it looks pretty good to me too.

 

To quickly check if you have MEN have a look at your supply poles, the neutral (top wire of the 4) should be grounded at every 3rd or 4th pole if you have MEN, if not sure I agree leave out the link.

 

[xtrnuno41]

A shower heater uses up to 4 kW, which is  4000/230= 17.4 A.  I calculate with voltage of 230 Volts, if 10 volts lower it increases, if higher it decreases 4.5%

I assume all sub units would be the same, as in the drawing with some of them i dont see the 20 A shower fuse. I guess they will all have the setting 20,16,16. You want every tenant to pay for their own use of electricity,  I again guess.

 

Extreme use scenario: 

If all people (4 rooms subs) take a hot shower only, at the same time, you are running 4 X 17.4 A = 69,6 A, split over 2 main breakers and cabling.

So per main breaker already passes 34,8 A, 2 times 17.4 A. Main breaker however is al ready over 63 A value

If all rooms are using as well the AC's 9000BTU, it cost another 1000 W/room = 1000/230=  5.3 A. Then 4 times if they all use it = 21,2 A.

Separated over 2 main fuses and cabling, Main breaker is then way over 63 A value

Meaning one main fuse for sub has then 2x17.4 A and 2 x  5.3 A =  45.4 A, that is already over the value of main fuse for the subs, which is 40 A. Fuse could stay in or maybe pop. All depending on device, which character B or C and state of the fuse. Beside that, if you are pulling in this scenario 2 x 45.4 A , you are way over the main fuse of 63A.

Then you should think as well also about your cables and quality(6mm2) if they can handle that. I did find a cable calculator and it said 10mm2.

Cable is all copper then ! 6 mm2 not enough, it came up 41 A. Of course doubling your cables works as well and maybe cheaper, but then do you have the space? I would have all subs on their own feed cables and not daisy chain.

 

With this scenario , i dont include on what people are having on their sockets, like a fridge or if they start also boiling water for coffee. 

 

I even didnt include the 5th room and the ground floor items, as the 5th room and ground floor will make the power consumption even bigger and has more effect on the total power consumption.

You all ready see in extreme scenario with 4 rooms you are all ready above 63 A value of your main fuse.

4 showers and 4 AC's brings it all ready up to 69.6 + 21,2 = 90.8 A. An additional room brings it up with another 22,7 A on total.

I think you have to go back to drawing board and start with 3 phase power instead of single..

Right?

 

[Crossy]

7 hours ago, xtrnuno41 said:

A shower heater uses up to 4 kW, which is  4000/230= 17.4 A.  I calculate with voltage of 230 Volts, if 10 volts lower it increases, if higher it decreases 4.5%

 

Heaters don't work like that, they are not constant-power they follow ohm's law, if the voltage goes up/down the current follows proportionately.

 

I agree that running everything on a 15/45 is marginal but usage diversity is your friend.

 

It is unlikely that everyone will shower at exactly the same time and even if they do the breakers he has will protect the installation (yes, they will kill the power either to just that floor or the whole place).

 

If the main breaker does open too often then the solution is a supply upgrade to 30/100 which may not be available or switch to a 3-phase 15/45 which would require some re-wiring of the incoming unit (supply 1 floor per phase).

Or just ask the room occupants to please stagger their shower usage.

 

If we ran all our A/C and water heating together we would be at about 100A, our 63A incomer has never opened.

[Crossy]

@Dwight You might consider adding voltage and current meters to your incoming supply so you can monitor usage so you have an idea how near the line you are actually getting.

 

I'd use RS-485 or WiFi enabled energy meters for each room. Read them remotely and also actually log energy usage. But that's just me ???? 

 

[bluejets]

I didn't see any mention of the route length of the sub-mains.

An important factor when calculating maximum demand and hence cable size.

The shower heaters are the killer here.

Edited February 16, 2021 by bluejets

[bankruatsteve]

14 minutes ago, bluejets said:

The shower heaters are the killer here.

His diagram shows 1 shower heater per floor.  Not a big deal.

Edited February 16, 2021 by bankruatsteve

[Crossy]

4 hours ago, bluejets said:

I didn't see any mention of the route length of the sub-mains.

An important factor when calculating maximum demand and hence cable size.

The shower heaters are the killer here.

 

Yeah, we are assuming a regular shophouse design which would limit the run lengths.

 

I'd also assume 3.5kW showers as the Thai "standard".

 

[Dwight]

Wow. First of all, thanks for all your comments and input. Good to know that my proposed drawing seems ok and I will take a look at the power poles to see if MEN is implemented or not, thanks @Crossy for explaining how I can check it.

 

@xtrnuno41 Thanks for your input. However there is indeed a lot of guessing going on in your comment. I did not forget to include any shower heaters. There is only 1 shower heater on each floor and as crossy mentioned it will be no more than 3,500W. The heaters will not be connected via the meters for the individual rooms. Each room has 4 sockets, 4 LED downlights and 1 AC unit. These are not apartments and there will be no cooking in the rooms.

 

As mentioned from others, this is a small townhouse of 3 floors with small rooms. If there is every any problem with breakers tripping my guess is that it will be the main 63A breaker tripping rather than the 40A breakers for the individual floors. In that case we might look into upgrading to a 30/100 meter.

 

For cable lengths, the longest supply cable going to floor 3 is probably no more than 10-12 meters. From any sub-unit to the shower heater the distance is less than 5 meters.

 

And regarding @Crossy 's comment about the energy meters..believe me if I was the owner of this house the entire building would be full of fun connected gadgets. Water level meters on the water tank, flow meters on the water pump, motor valves, temp sensors and of course connected energy monitors on all consumer units including the main breaker box. Probably with push-notifications to my phone if we are getting close to the line.. But that's just me???? By the way I just saw found your old post about your Arduino power meter. Will take a closer look on that today, very interesting!

 

Thanks for all your help!

 

Best,

Dwight

[xtrnuno41]

13 hours ago, Crossy said:

 

Heaters don't work like that, they are not constant-power they follow ohm's law, if the voltage goes up/down the current follows proportionately.

 

I agree that running everything on a 15/45 is marginal but usage diversity is your friend.

 

It is unlikely that everyone will shower at exactly the same time and even if they do the breakers he has will protect the installation (yes, they will kill the power either to just that floor or the whole place).

 

If the main breaker does open too often then the solution is a supply upgrade to 30/100 which may not be available or switch to a 3-phase 15/45 which would require some re-wiring of the incoming unit (supply 1 floor per phase).

Or just ask the room occupants to please stagger their shower usage.

 

If we ran all our A/C and water heating together we would be at about 100A, our 63A incomer has never opened.

Well, I mentioned an  "extreme scenario" , it can or not. All is possible, only just showed. You will find out in real if you ignore.

No matter what heater, if you want water of 40 degrees to shower in short time, you need the power to heat.

It cost you no matter a lot in electricity, up to 4 kW. 

Yes im aware of ohm's law. I mentioned it, as i was calculating with 230Volts. Standard in EU, but Thailand 220 volts?

Never measured yet, but on google  there is even both saying? 

So with 220 volts, it will bring up the amps with 4.5 %. Meaning 18.2 A for the heater.

 

With your 63A fuse (probably C type fuse), you know it switches in 5-10 In. With 100 A running(1.5 In) the system has about 40 seconds to go down again before it trips, thermal. Until that time it stays in. Looks like you are lucky it changes in 40 seconds, 555. 

[xtrnuno41]

7 hours ago, Dwight said:

Wow. First of all, thanks for all your comments and input. Good to know that my proposed drawing seems ok and I will take a look at the power poles to see if MEN is implemented or not, thanks @Crossy for explaining how I can check it.

 

@xtrnuno41 Thanks for your input. However there is indeed a lot of guessing going on in your comment. I did not forget to include any shower heaters. There is only 1 shower heater on each floor and as crossy mentioned it will be no more than 3,500W. The heaters will not be connected via the meters for the individual rooms. Each room has 4 sockets, 4 LED downlights and 1 AC unit. These are not apartments and there will be no cooking in the rooms.

 

As mentioned from others, this is a small townhouse of 3 floors with small rooms. If there is every any problem with breakers tripping my guess is that it will be the main 63A breaker tripping rather than the 40A breakers for the individual floors. In that case we might look into upgrading to a 30/100 meter.

 

For cable lengths, the longest supply cable going to floor 3 is probably no more than 10-12 meters. From any sub-unit to the shower heater the distance is less than 5 meters.

 

And regarding @Crossy 's comment about the energy meters..believe me if I was the owner of this house the entire building would be full of fun connected gadgets. Water level meters on the water tank, flow meters on the water pump, motor valves, temp sensors and of course connected energy monitors on all consumer units including the main breaker box. Probably with push-notifications to my phone if we are getting close to the line.. But that's just me???? By the way I just saw found your old post about your Arduino power meter. Will take a closer look on that today, very interesting!

 

Thanks for all your help!

 

Best,

Dwight

OK , i thought every room had their own shower. Misunderstanding my way.

About the heater, just picked one in internet, there are several from 3500 W and up, so i took the 4000 W.

[Crossy]

8 hours ago, xtrnuno41 said:

but Thailand 220 volts?

 

It's worse than that.

 

In the PEA area (most of Thailand) the supply is (very) nominally 220V phase-neutral.

 

In the MEA area (metropolitan Bangkok) the supply is nominally 230V phase-neutral.