protective bonding conductor size

[CFTIS]

Hi guys, I've questioned something at my workplace and after receiving my answer I'm not overly convinced and would like some other experienced gods to chime in

On a new install in an existing property today I went to bond the Water and noticed it was already done, clearly many moons ago before we done the job.

The protective bonding conductor was 6mm, this is what I questioned as to my knowledge I believed it should've been a 10mm.

I was going to pull in a 10mm (probably a 2 hour job) but checked with my boss first, he said to speak to his business partner (my other boss) as he does all our testing and inspecting.

The property has a TNCS system and what I was taught was that the protective bonding conductors are to be sized according to the copper equivalent csa of the supply neutral conductor, So according to the values in Table 54.8 with the neutral having a 25mm csa it should be a 10mm bonding conductor.

My boss asked me if it was a new house, which I replied no.
He said 6mm was fine, it wouldn't fail a test it would only be an advisory.
He said 10mm would be preferred but it wasn't something you could tell the client they had to have done only mearly advise them.

thoughts?

 

[MDJ]

yes we know, what do you really think?

 

[CFTIS]

??

 

[westward10]

This is that old 6.0 on TN-C-S scenario. The 15th Ed never quoted minimum sizes for this type of earthing system but to consult your supplier so when you do find 6.0 bonds you have no way of knowing if they were ever the correct size in the first place.

 

[telectrix]

apply the adiabatic, having measured the PEFC. that will give min. sizeof main earthing conductor. bonding conductors need to be no less than 1/2 the size of the MEC. although 10mm is specified for pme systems, then it's would be a C3 in a EICR. tin hat on, ring crimps installed on my back boxes in a previous thread, beer on table, awaiting the flak.

 

[Leesparkykent]

BTW just for future reference It’s sized to the incoming neutral not the CSA of tails.

 

[Midwest]

apply the adiabatic, having measured the PEFC. that will give min. sizeof main earthing conductor. bonding conductors need to be no less than 1/2 the size of the MEC. although 10mm is specified for pme systems, then it's would be a C3 in a EICR. tin hat on, ring crimps installed on my back boxes in a previous thread, beer on table, awaiting the flak.

Where PME conditions apply, is it not selected via table 54.8?

 

[Deleted member 26818]

Where PME conditions apply, the minimum CSA for both the earth and bonding conductors is 10mm2.

Where PME conditions do not apply the CSA of the Earth conductor should be determined by use of the adiabatic equation or by use of Table 54.7. The minimum CSA for the earth conductor is 2.5mm2 (where mechanically protected) or 4mm2 (where not mechanically protected). The minimum CSA for bonding conductors is 6mm2.