Is the MET an exposed conductive part?

[ConnorLondon]

Hi all,

while working on the bonding task of the L2 G&G I assumed the supplementary bonding CPC should be 4mm2 due to the table in the OSG -(p.51. size of protective conductor = 16mm2)

However another student said the MET is an exposed conductive part so the CPC should be 6mm2 - even though the table if true says 10mm2. I find this confusing as I thought a exposed conductive part needed to have a line conductor in order to be in danger of going live? Also, if the supplementary bonding for a bath pipe can be 4mm2 from the lighting rose in a bathroom how is this any different from the MET which provides earth to the whole system?

Looking through the BS 7671 I couldn't find a definitive answer.

Any help clarifying this is much appreciated.

Thanks,

Connor

 

[Electro-tech]

Take a look at Part 2 DEFINITIONS & look at MET . Also, all the earthing definitions, CPC sizes are related to the Type of Supply & Line conductor sizes aswell.

 

[ConnorLondon]

Thanks so much for your pointers.

After reading the sections you suggested and reviewing the assignment again it seems like the CPC should be 10mm2 if it's coming off the MET. However if it's coming off the water mains water pipe as a supplementary bond then it can be 4mm2 - I think... I'm not really sure where the 6mm2 is coming from?

Thanks again for your help.

Connor

 

[Electro-tech]

Need to know more about your assignment as to type of supply Tns etc. I think you are getting confused between protective bonding & supplementary bonding. Study Part 4 Onsite guide.