CPC size in 3 Phase . Please your expert advice ???

[pantaiema]

Dear Expert
BS7671 tbale 54G mention that for:

CSA <= 16 CPC size=size of phase conductor
CSA 16<CSA<= 3 CPC size=16
CSA >35 CPC size=CSA/2

My question is that:
it is also for 3 Phase Circuit or Just for 1 Phase

Let say I need to supply TP+N Distribution Board with Phase conductor with CSA= 100 mm2. Assuming that I do not want to calculate using adiabatic equation but just using this table:

Is it true that the CPC size should be 50mm2 (Assuming CPC have the same materials with phase conductor) ?.

Thank you very much for expert advice

Pantaiema
Still Junior in this field

 

[Spark123]

Yes

 

[plugwash]

think about things for a minuite

an earth fault is going to be from one phase to earth so the other phases shouldn't make any difference to the earth conductor size.

 

[Lectrician]

also, 100mm² doesn't exist - closest would be 95 or 120.

But thats not the point.

Always go half the size of the phase or neutral is the rule.

So, 25mm² phase/neutral would want a 12.5mm² earth, hence we use the next available size of 16mm²

A 185mm phase/neutral service would want a 92.5mm² earth, so we would use a 95mm²

Not many people will use the adiabatic equation, they will use the table, and install like that - ignoring the value of the SWA armouring if present.

 

[pantaiema]

Thank you very much for those who took time to answer my question.
Yes indeed, I quote the wrong cable size.

Regards
Pantaiema