Example of use of Adiabatic Equation.

[i=p/u]

yeah! they follow quality and continuity regs.

 

[mambo76]

Thanks

 

[steveberry11]

so im trying to work out the minimum size main earth for main supply ze=0.11 its a tncs supply i would say k=143 and for the main consumerunit i would say its 5 second disconection time so
230/0.11=2091
so doing the caculation i get 32.9mm and this cant be right what am i doing wrong it must be T
a bs 1361 will go quicker than 0.1 s at that fault curent.
so taking pg 244 time/current characteristics for 1361 60 a fuse at 5 seconds is 330A so doing the calc again i get 5.16mm this is better but what is right or for a consumerunit disconection time is it 0.4
please help i done it on a pir with a 6mm main earth which i doubled up to 12mm but minimum size is 5.16mm now this is safe just not conforming to bs7671 2008

You are incorrect with your 5 second disconnection time. The disconnection time is worked out by finding the fault current and using the time current curves in the Green book.

 

[steveberry11]

This equation allows you to calculate the CPC size only this must be used as a part of a cable calculation not just by its self. As you also need to take into account your R1 + R2 & Zs calcs.
You can not use this for main earth or bonds. You need the green book for that.

 

[pencilpusher]

Sorry wrong post! Have moved it.

 

[Mick Jefcoate]

Just a quick question on the rules in maths if this thread is still live. In the equation do you apply the sq root before before deviding by the K factor ? If you do the sq root last, the answer is vastly different.

Mick

 

[Richard Burns]

Just a quick question on the rules in maths if this thread is still live. In the equation do you apply the sq root before before deviding by the K factor ? If you do the sq root last, the answer is vastly different.

Mick

Do you apply the sq root before before dividing by the K factor?
Yes

 

[Mick Jefcoate]

Thanks Richard, everyone I asked had their own opinion but nothing based on fact.

 

[James-]

Cheers