Choosing the correct circuit breaker value

[Sofiane]

Hello.

So, I would like to know how I can choose the correct circuit breaker value when doing a new installation.

My example is: I have 16 rooms. Each room has its own electrical board (main breaker is a 220v, 32A, a lighting cb and one for socket outlets) I want to add a LV switchboard or a distribution panel (not sure which is the right term to use) in the distribution panel I thought I'd use 4 380V, Circuit breakers, each one would be feeding 4 rooms (in order to reduce costs) but I don't know how I could select the correct cb value. I can determine the exact current consumption for the lighting system, but I have no idea what would be plugged into those socket and how much current would be consumed. So how can I choose these CB. Also how can I choose the main CB in the switchboard

Also, as a side question. Is there like a rule of thumb when it comes to choosing the main CB? Assuming I have 5 4P 40A CB with no extra information on what they're feeding, is there a way to choose the main CB in this case?

Thank you in advance

 

[pc1966]

A 16 room set-up is a bit beyond DIY so probably you should be looking at a suitably qualified electrician locally.

It appears from your profile you are located in Algeria and I have to say I have no idea of what the local regulations and rules are for your country so while I can comment on UK practice, it may not be suitable for your region.

Basically the CB has to protect against fault (so damaged cable, etc) as well as overload in most cases. Choosing that depend on the cable specifications as well as the nature of the supply and routing of the cable, etc.

Also you need to balance those factors against the typical loads you will have, and usually that means you need to know a bit more about the planned usage as if you simply add up all 16 rooms of 32A socket circuits you are going to need a supply that may be larger than you have.

Finally it is normally a requirement that if there is a final circuit fault then the local breaker/fuse goes and the supply remains on for other uses, referred to these days as selectivity. Achieving that can be difficult and expensive (e.g. using MCCB for the sub-main circuit protection) or requiring electrical skill to safely replace (if fuses used). But there are many other factors here to be considered.

 

[Lucien Nunes]

There are various methods to estimate loading of general-purpose socket outlets, which are sometimes encoded in local regulations, so that is the first place to look. As with @pc1966 I am not familiar with Algerian practice although it is IEC-based (as opposed to NEC-based) and possibly comparable to the French implementation of IEC. A design engineer familiar with the local building codes, electrical regulations, and local expectations of level of provision will doubtless have rules of thumb for each different type of building usage and design.

Heating and cooling often account for the largest fraction of the general loading, so it's often worth looking at the installed HVAC equipment and evaluating whether there is likely to be a requirement for local heating and cooling plugged into sockets. A building with a comprehensive HVAC scheme is less likely to have a lot of local portable A/C units running than one without, while a building in a temperate country is more likely to see portable heaters in use than one in the tropics.