Note that the 6 sockets are in ring configuration. Just in case you are not sure what it means. The ring wiring is when wires come out from DB and go to sockets in series and return back to DB through another path to form a circle. Therefore, if you cut wire to one of the socket, power will still be available on the rest of sockets. My house wiring is like this. There are two separate rings for ground and upper floors. I have 2x32A MCB in my DB.

Just think you MCB is more on protecting wire in wall. If current is too high, the MCB will trip to protect wire in the wall from getting to hot and melt the insulator, short-circuited and ignite fire. The MCB rating is not rated to provide total power to sockets on the wall. As you can see the 20A MCB is used for 2x13A socket. Two sockets totaled up for 26A but the MCB is only 20A.

Current carrying capability of wire depends not only on its size but ambient temperature and how it is laid also affect current rating. I always assume the 4mm wire should be protected by 20A MCB even though it can carry much more current. If in thermally isolated trunking in will be rated at 24A but if laid directly on concrete wall it can go up to 32A. However, you have other wires put together.This will affect ambient temperature as well.

Hope this helps.

https://www.st.gov.my/contents/publications...uildings%20.pdf

Thank you. Got to plan for my house reno next year. At least I learn some knowledge so not be easily deceive by contractor.

Thank you. That helps in my understanding


This post has been edited by YoungMan: Nov 12 2024, 09:49 AM

yeah.. so much to learn from members here.. How I wish this thread started in 2012 instead.

Need to follow cable size. Not socket qty
Avoid ring if possible. If the ring break, mcb won't trip even when overloaded

I would love to see the St publication.

Cable size is already defined for lighting and socket. Why ring will not trip if overloaded? The current to MCB is still total of two separated string of loads. Note that each socket is still protected by 13A fuse.

Ring uses loop. If the loop is broken
The only become 1 wire feeding the socket instead of two.

Yes, but the wire is still the 4mm wire for the socket as standard

https://www.st.gov.my/contents/publications...uildings%20.pdf
page18

here say ring use 2.5mm2 and mcb 32amps.


if ring use 4mm2, then no issue.

I see what you meant. I did not look into drawing detail. I am wondering if the 2.5 and 4 is actually the surface area. When I look at the wire, it looks like the wire diameter not area If it is really the 2.5mm², then the diameter is only 1.78mm.

Anyway, even if the area is 2.5mm², the wire will survive much longer than the MCB tripping time based on what I used to read before. Anyway, not good as you say

Very sorry, but you have made a mistake, as lj0000 has also pointed out to you. I reproduce the diagram from the ST document you linked to below



The MCB protects the wires from melting, not you put a 32 A MCB you can have 4 socket outlets. The wire sizes are stated in the diagram, and are the determining factor for the MCB rating. You can see the ring circuit is using 2.5 mm². (2 x 2.5 mm² = 5 mm², which is larger than 4 mm²) That is the Cross Sectional Area of the wire, not diameter.

lj0000 also points out that in the ring circuit a wire may be disconnected, and then it becomes unsafe. This really happens from my experience, as different techs will service the wiring without knowing the ring connection. There is also specific requirements if you want to branch off from a ring circuit. I do not like ring circuits for these reasons.

Avoid ring as much as possible
It's designed during WW2 as copper shortage

Except it won't. Pull 30 A through a 2.5 mm² ring circuit protected by a 32 A MCB, and if one of the wires is faulty, the wires will overheat well before the MCB trips.
Here's the thing - a ring circuit that has a faulty connection/wire still has power so you don't know it is faulty - until you overload it and things catch fire.

Yes I understood what you said. I also mentioned that the MCB is more on protecting wire in the wall, not appliances.

My house is ring and it is using 4mm wire, not the 2.5mm like in diagram. I was not looking at the diagram because for me any socket is using 4mm . My mistake there. The reason I mentioned about area vs diameter was because the 2.5mm² wire has less than 2mm diameter which is very small and makes me wonder if it really the area.

One reason for using a ring circuit is so that you can use under specced wires to perform like larger wires, ie 2 x 2.5 mm² wires can perform like 4 mm². Did your installer tell you they used 4 mm² in a 32 A ring circuit, and did you confirm this for yourself?

Because it makes no sense to use 4 mm² in a ring circuit as 4 mm² is already rated individually for 32 A. Now if you said the ring circuit is 50 A but using 4 mm² then it makes sense.



(Slight aside : The other reason for a ring circuit is to ensure less voltage drop over the wiring for very large areas. Malaysia supply is 230 V +10% -6%, so minimum of 216.2 V must reach the appliance.
2.5 mm² wire has a resistance of about 7 ohm per km.

So according to the online calculator, it would require 49 m of 2.5 mm² wire length to drop that 13.8 V at full 20 A loading. I guess it is possible if your incoming is already low, and you area is very large, but my experience is TNB supply is always on the high side)

Why it makes no sense? It is better, isn't it? The wiring is original from developer and I know it is a ring because I checked it myself. There is no voltage problem and it is just normal semi-D house size in Malaysia to concern about voltage drop in wire. I did extend a bit at the back of the house and I pulled another big cable from main DB to another DB I added at the back of the house to supply power for kitchen, air-cond and heaters to rooms/bathrooms at the back of the house. The kitchen is electrical hob, hood and garbage disposer. Developer only provide power points for air-cond and heater to master bedroom only. My friend and I got cables laid down during renovation work.

It makes no sense to me because it increases cost, increases complexity, increases installation work, increases points of failure, increases the chance of being done wrong (see conduit fill, proper torque for terminals, number of wires into a terminal) and is so unnecessary to do with 4 mm² at 32 A. There's also no benefit of increased current carrying capacity, as your MCB is C32 anyway. And you also say that the area is not that large, so no reason to do it for voltage drop in the wires.

I contend that a simpler system that does the job properly is always better than a complex system.

As for benefit, well it is a fully redundant system since you say the wires are 4 mm². Is this "better"?.... if you think it is better then it is.

Ring circuit is actually good for when you need a lot of socket outlets in a room ( & won't be adding anymore) but the total load is not high. I would pair 2.5mm² ring with 10ma C25 RCBO with FE as this is the most easily available 10ma RCBO with FE. This is useful for washing machine + dryer & bedroom with socket outlet in bathroom. Ring circuit is actually easier for me to check the continuity/resistance of the wiring. But if you're using Sirim non-JKR cable, you must not use 2.5mm² cable with C32 breaker as most of them actually 14AWG (~80% cross section area & ~90% current capacity of actual 2.5mm²). I don't like circuit spanning multiple area/room. There is no point using 4mm² ring circuit for socket outlets even for kitchen. Just use multiple C20/25 4mm² radial circuit. For 13A plug appliances, they are usually rated for <10A (2-2.4KW) for long continuous operation type or <13A (3KW) for short operation type. Use double socket outlets to distinguish the circuit grouping.

As long as you never thermally overload cable and protect it from the environment, the cable insulation can easily last >30years even for sirim certified non-JKR cable. This is easy to follow for fixed appliance each having it's own circuit even after derating the cable for the ambient temperature (I use 50°C for hot kitchen and roof ceiling). Socket outlet circuit is where people mess up with excessive looping or not know the circuit grouping of the socket outlets. You might have 3 separate C20 2.5mm² circuits, but that won't stop them from overloading 1 of the circuits with powers strip extension. To prevent the cable the from being overloaded, just make sure the MCB overload current (1.45x) didn't exceed the cable current carrying capacity.

It is good say when the current in conductor is constantly high for long period. This will lower the wire operating temperature compare to smaller gauge. PVC insulated cable operating at 1x current load at 70C will have service life for 20 years.

Lasting 20 years?!!

I have installations from 1990 still going strong till today