Help cable calculation please newbe

[Cornish1984]

I have a design unit and 14 circuits to do. Can some one please help as I have completed 1 of my knowledge and before I crack on any help on this would be great. It's a rough copy so excuse the mess. Thanks. It's question 4. Thanks

 

[Cornish1984]

They told me to add these together am stressed lol. A thought I would just use 1 ze. But there is an existing block with a supply As Well

 

[Cornish1984]

I have changed the whole circuit and recalculated it. I hope it's right because I have done another 2 circuits View attachment 43144

 

[Cornish1984]

Sorry my head is done in as I have basically been left in the lurch and I finish next week hmm. It's appreciated tho allot Richard. They know I am a little dyslexic but I started course late and because of founding am 33yr old.

 

[Cornish1984]

That's the 1st 1 I re done m8

 

[Richard Burns]

Sorry I am out of time at the moment, but on a quick look the actual Ze at the origin of the installation is 0.09 Ω.
Then there is a supply to your distribution board and at that board the Zdb is 0.11 Ω, note this is different from 1.01 Ω.

For your calculation use the value 0.11 Ω as the additional resistance from the non final circuit part of the fault path, equivalent to Ze for your calculations.

On a quick view the numbers look right for your first post about circuit two but disconnection times are on p.55 not p.58.

On the redone one you have the calculation for volt drop wrong.
The answer you get (6.2V) is for a mV/A/m value of 19, which would be 2.5mm² cable.
You have written the calculation using 31 which is the value for 1.5mm² cable. This makes all the following calculations wrong because the cable size is incorrect.

 

[Cornish1984]

Thanks m8 appreciated allot Richard I will drop back on that 1. Diamond