PNB Protective Earthing Systems - Bonding Conductor Size

Question

I was interested to read this article https://professional-electrician.com/technical/protective-earthing-systems-whats-the-difference-between-pme-and-pnb-eca/ 
 It includes the following "... TN-C-S PME installations are treated akin to where PME conditions apply, where the maximum size of the main protective bonding conductor should not surpass 50 mm&sup2; of copper conductor." 
 I'm certainly not current on the Wiring Regs., but I was interested in the concept of specifying the maximum size of bonding conductor. 
 Obviously cost and physical constraints would limit maximum size, but what's the rationale for a technical specification of maximum conductor size?

mapj1 · Accepted Answer

And there is nothing to stop you using a larger conductor if you wish to do so - it is more that the recommended size stops going up at 50mm2 ,because substations and fault current stop getting bigger much beyond the 1MVA/ 30kA level, so the rule of thumb has a limit. 
 Also of course, unspoken, is an assumption about the length of that bond, and the area of the equipotential zone there may be corner cases where it is not the right thing to do. 
 Mike.

AJJewsbury · Answer

where the maximum size of the main protective bonding conductor should not surpass 50 mm&sup2; of copper conductor." 
 
 I agree it sounds like a poor choice of words - "need not surpass" - might be been technically more accurate (at least in terms corresponding to my understanding). 
 - Andy.

PNB Protective Earthing Systems - Bonding Conductor Size

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