tn-c-s earthing

[stevieffc]

Hi just wondered what the rule of thumb is for calculating the main protective conductor is in a tn-c-s system as l have a supply with 185mm cables and a 50mm main earth?

 

[Bobster]

Adibiatic equation.

 

[Hobsoni]

Hi just wondered what the rule of thumb is for calculating the main protective conductor is in a tn-c-s system as l have a supply with 185mm cables and a 50mm main earth?

Amtech Pro

 

[Bobster]

Amtech Pro

I think that's a case of running before walking.


I don't fully trust amtech, I've had numerous times it throw out funny information.

 

[Hobsoni]

To be fair your probably right.

I have not had the pleasure (or the bank balance) to be able to utilise the software.......I believe you would always cross check the calculations for the sake of accuracy though.

 

[Deleted member 26818]

Hi just wondered what the rule of thumb is for calculating the main protective conductor is in a tn-c-s system as l have a supply with 185mm cables and a 50mm main earth?

50mm² should be fine.
What do you have, a 200A supply?

 

[Bobster]

To be fair your probably right.

I have not had the pleasure (or the bank balance) to be able to utilise the software.......I believe you would always cross check the calculations for the sake of accuracy though.

My copy's company owned, and yes I do when I can scribble out the workings on a peice of paper.

 

[stevieffc]

no its a 400A supply

 

[Deleted member 26818]

What's yout PFC and type of protective device?

 

[stevieffc]

8.9KA and protective device l think is a BS 88

 

[Hobsoni]

no its a 400A supply

Is it in a dedicated control room? I imagine must be.

The reason I ask is because designs we had required our control room to have a 70mm bare copper earthing conductor buried around the perimeter of the building linked to 4 electrodes at each corner with 2 x 120mm pvc copper links going to an earth plate..............with the CPC of the panel supply linked via the earth plate too.

Have your designs specified any additional protective earthing or earth bonding to take place??

 

[Deleted member 26818]

8.9KA and protective device l think is a BS 88

I imagine with that PFC, you would be looking at a disconnection time around 0.1s, which would give a CSA for the CPC of about 20mm².
As such, 50mm² should be fine both as a CPC and Bonding conductor.

 

[stevieffc]

Thanks for your help much appreciated

 

[Plonker 3]

That will be this weeks homework completed then.