10mm twin & earth supllying DB

[calv68]

Hi everyone ive been to look at a board change in a two bedroom flat the db is supplied from a meter room with 10mm twin & earth via a 63 amp switch its a tncs system. The earth from the met in the meter room to the 63a isolator is 16mm but from there to the db is only 4mm coming from the 10mm twin & earth, its clipped direct so can draw 64 amps is this within the regs

 

[Darkwood]

Just answered a similar question (25mm t&e if you have a look), if an earth wire supplies the earth path for multiple circuits then its required to be equal to or greater than the associated phase conductor also take into account if equipotential bonding is required from the submains then an allowence in csa of earth must be considered too.

 

[johnsparks23]

any chance of explaining the point on equipotential bonding from a submain , in regards to csa.
great aswer, well explained, many thanks darkwood.

 

[calv68]

its 16mm to the enclosure which includes a 63a switch and earthing termonal in the meter room then 10mm twin & earth to the flat its about a 6 metre run

 

[Darkwood]

any chance of explaining the point on equipotential bonding from a submain , in regards to csa.
great aswer, well explained, many thanks darkwood.

Its just a reminder that the incomming supply denotes the size of the equip' bonding conductors especially where tncs(pme) systems come in, and your equipotential bonding may exceed the submain earthing size even with your additional earth thus requiring a larger earth to each flat as they may need to be treated as a seperate installations with regards to equip' bonding depending on the building layout thus requiring local equipotentail bonding to submains.

 

[sparks1234]

Just answered a similar question (25mm t&e if you have a look), if an earth wire supplies the earth path for multiple circuits then its required to be equal to or greater than the associated phase conductor also take into account if equipotential bonding is required from the submains then an allowence in csa of earth must be considered too.

Can you clarify where it says this in the regs please

 

[Darkwood]

Can you clarify where it says this in the regs please

Check out reg' 543.1.2 and when talking about the equip'bonding and allowing for it, if you have a common supply to multiple premises and each unit is independant with its own access it must be regarded as a seperate installation and thus bonded at the imcomming point to said premise, this regulation spans further than the red book but into fire regs and building regs, so if the main bonding requires 25mm at origin it will also require the same at common premises to supply:- therefore the earth to said premises needs to be adequate to allow for equip' bonding. This is more so when dealing with TNCS as eddie curents can circulate around the earthing system hence the larger cables required compared to TNS.
I fell foul of this myself as the regs dont mention this situe but the NICEIC inspector got me on it, but after the explanation i can see the reasoning behind it.

 

[mark_the_spark]

Check out your on-site guide, P15 & 16, "General layout of equipment"

if you have equipotential bonding going to the C.U. fed from the 10mm t&e then your earth is not big enough. I would run a 16mm myself

 

[Spudnik]

But thats only if you export PME though?

I havent read the whole thread

 

[mark_the_spark]

But thats only if you export PME though?

I havent read the whole thread

Nope thats for a TN-S or a TN-C-S system