Main earth and bonding csa?

[DavidJ91]

Hey guys, I'm getting a bit confused with regards to the regs for the sizing of bonding/main earth. Anyone able to shed some light on the regs or point me to the exact one?...

I'm feeling my way here, but isn't the CSA of an earth usually 67% smaller than that of the conductors it's earthing?

 

[tony mc]

I think you are mixing up the size of the CPC which is incorporated in twin and earth cable as the CPC is generally smaller than the main conductor.

IE 2.5 twin & earth has a has the main condutor of 2.5mm and the Cpc 1.5 mm.

2.5/1.5 =1.67 ratio

4.0/1.5= 2.67

6.0/2.5=2.4

Etc

However 1mm twin & earth is 1mm/1mm so its the same.

The CPC has to be large enough to carry the fault current which could flow in the event of a fault to disconnect the protective device in the required time.

Hope this makes sense.

 

[Chr!s]

I think you are mixing up the size of the CPC which is incorporated in twin and earth cable as the CPC is generally smaller than the main conductor.

IE 2.5 twin & earth has a has the main condutor of 2.5mm and the Cpc 1.5 mm.

2.5/1.5 =1.67 ratio

4.0/1.5= 2.67

6.0/2.5=2.4

Etc

However 1mm twin & earth is 1mm/1mm so its the same.

The CPC has to be large enough to carry the fault current which could flow in the event of a fault to disconnect the protective device in the required time.

Hope this makes sense.

You've got some of your ratios mixed up there Tony


Regards Chris

 

[alanl]

Also, this talk of 'main earth' and 'bonding' does not do any new readers any favours, they are not the terms used now, so we should be using 'earthing conductor',* 'main protective bonding conductor' and 'supplementary bonding conductor', as well as 'circuit protective conductor'.