Main Bonding csa when earthing csa calculated

[timhoward]

Just double checking please - in situations where the main earthing conductor csa is calculated, and in a TNS installation, the 50% bonding conductor csa rule still applies to your final calculated and rounded up earthing conductor size? (As opposed to the tabulated size)
I'm doing remedials and someone else gave a C2 for the main earthing only being 6mm csa as line conductors are 16mm, and also gave C2 and said the 6mm csa main bonding should be 10mm. It is very definitely TNS.
However the formula confirms that in fact 6mm earthing is fine (it's a sub main with C32 breaker protecting it and low PFC), and as long as the 50% is based on the 6mm I can't see why the main bonding is an issue either.

 

[westward10]

So it's a cpc not an earthing conductor?

 

[timhoward]

So it's a cpc not an earthing conductor?

Thanks, yes its a CPC. I confused the terms because it feels like a normal house....

 

[westward10]

So the main protective bonds are located at the end of this submain and supported by the 6.0 cpc.

 

[timhoward]

In fact more complex. Looked more closely now.
16.0 cpc as far as adaptable box (one core of SWA). 16.0 cpc to an MET block. 10.0 cpc from MET to CU.
Bonding conductors to gas, water are 6.0