How to work out the total design load to find my swa cable size

[Ted Curly]

I have worked out the total ib of the circuit at 169.88amps and with added diversity came up with 120.36amp,,,, but if I do the 3 sockets rings as 20amp radials diversity will come in at 96.36amp..

 

[Pete999]

Yes this is very true my original plan was to have the ring wired but leave the returning legs unconnected and make it 3 16a radials, and have the legs there if ever needed in the stud wall

Not a good idea Ted, how did you intend leaving the end of the leg?

 

[Ted Curly]

The walls are stud walls, the sockets will be in fast fix boxes, the 3 return legs can be kept in floating in the wall not connected at either end as it is my uncle I feel it would end up beening a ring and more sockets added eventually knowing him.

 

[Pete999]

The walls are stud walls, the sockets will be in fast fix boxes, the 3 return legs can be kept in floating in the wall not connected at either end as it is my uncle I feel it would end up beening a ring and more sockets added eventually knowing him.

20 Amp Radial Circuits is the way to go Mate. Leaving dead newly installed cables, could cause confusion.

 

[The Ghost]

silly I know to worry about future use

Required not silly!

 

[Spoon]

Look at this logically.
You have three 3kW heaters. Two instant water heaters at 3kW each.
I'm presuming that the heaters are going to be thermostatically controlled and you will have these on a timer that will come on first thing in the morning. So that the place is warm. No one else will be in then. No one wants to walk into a place to have their nails done and it's cold.
By the time people are in, the place should be up to temperature. So that just leaves the heaters ticking over, hardly using anything. Also your two instant heaters, sockets and lights.
As you have not told me that are going to be plugged into the sockets I'm going to guess its not going to be more than 3kW.
Use LEDs for lights.

So the max demand you will most probably have is first thing in the morning, when all 3 heaters kick in. 9kW... Say 40A

 

[Ted Curly]

With the 20amp radials diversity will be at 96.36a = 22kw, the swa at 40meters run will have to be 16mm minimum for that much as the run is so long, the lighting all on leds, and the sockets will have a kettle, fridge, plug on lamp and few small face machines. At the house end the swa can either be placed into the existing board or on its on sub supply I just worried about earthing then as would it not require a delayed rcd at the house end, was considering a tt as its so far from house.

 

[Des 56]

What is your thinking regarding a time delayed Rcd for armoured cable ?
What earthing system is at the supply end to make that so ?

 

[davesparks]

With the 20amp radials diversity will be at 96.36a = 22kw, the swa at 40meters run will have to be 16mm minimum for that much as the run is so long, the lighting all on leds, and the sockets will have a kettle, fridge, plug on lamp and few small face machines. At the house end the swa can either be placed into the existing board or on its on sub supply I just worried about earthing then as would it not require a delayed rcd at the house end, was considering a tt as its so far from house.

Why does the submain need RCD protection?
Why does the distance matter in the decision to create a new TT earth?

 

[Ted Curly]

Hi the earthing arrangement is TN-C-S and 100a supply, I was thinking time delayed if was going into existing board as not to trip the house, or just Henley block and have its own sub board non rcd at house end and having a tt at outbuilding end