How many way board?

[MrGwythers]

This is an apprentice question so only for learning purposes.
When choosing what way board you should use, weather it be new build or rewires.

What are your methods, do you go by how many circuits are in the board already and go for say a 10 way with 8 circuits existing and 2 spares or by intake fuse size and then work out maximum demand for the installation.

I see alot of these double stacked consumer units and just wondering how they are fitted without blowing the fuse even with diversity there's alot of circuits in the board is that a good practice? Would they only be used on 100A intakes?

Hope that's all understandable, thanks

 

[Dustydazzler]

So many lighting circuits nowdays are rated at 6a at the board but due to led lamps barely pull 0.5 of an amp even with all the lights turned on.
Very rarely will a standard domestic house pull more than 100a not unless you are all electric with a couple of electric showers on the go at once.

 

[Lister1987]

Work it out, a 2 up 2 down is likely to have 2 rings, 2 lighting circuits, a cooker, shower and boiler and possible garage/conversatory.

8 circuits, across either 2 RCDs or all RCBO so either 12 way (8 slots for MCBs and 4 for 2 RCDs) or 8 way if all RCBO - the above assume that the main switch/SPD rant included in the useable way count.

 

[Andy78]

A good rule of thumb is 20% spare ways for future use.

If it's a new build or rewire like you have stated then you will know exactly how many circuits are being installed.

More circuits does not mean more current draw. The current drawn depends on the loads connected.

 

[telectrix]

count how many circuits on existing. add any more for anything else you are installing if applicable, then ad 2-3 spare ways for future expansion. don't forget space for SPD or AFD if required.

 

[davesparks]

Count the number of circuits you need, add a few for spare capacity.

Or just get the biggest board you can to give you extra working space inside it.

 

[MrGwythers]

So from what you all say it doesn't really matter what size board you put in, just comes down to the loads that get installed.
Thanks for the help guys, much appreciated?

 

[Dustydazzler]

Exactly

Nothing to stop you putting a 21 board in a 1 bed flat if you really wanted to

I think the reason you see many over sized boards these days with lots of spares is that the price between a small board and the biggest domestic board is just a couple quid

No issue having 6 or 7 spare ways and just blank them off

 

[Mike Johnson]

Installing an SPD with MCB protection on a three phase unit that's another eight ways gone on the board, without being three phase it would still be four ways extra, then an AFDD, that's another three ways, so the latest regs have introduced at least another seven ways into our board, from what I have seen in the UK none of the current boards can take that type of extra installation and still comply with spare ways, looks like the manufacturers for the UK will have to start selling EU boards.