remedial works after a periodic???

[MARTISPARKY]

Im about to carry out a change of consumer unit as a major job for the nic domestic installer inspector... now what i need to know is do i need to upgrade the supp bonding conductor from its original 6mm to 10mm for the installation to pass??? answers on a post card please...

 

[Apache]

Hello and welcome to the forum

AFAIK no need for supplimentary bonding with a 17th CU

What's the earthing arrangement?

 

[sparky999]

Is it close to the board or is it some distance away?

 

[MARTISPARKY]

its a tn-c-s system and the main gas and water are at the opposite end of the building...im planning on a full rewire this time next yeAR , just need to know will the nic man fail me if i do not upgrade it or is mentioning it in the observations and recommendations in the pir good enough..??

p.s. what does afaik mean??? ?:|

 

[Apache]

AFAIK as far as i know

no need to supplimentary bond, you mean main bonding!

 

[MARTISPARKY]

sorry yeah main bonding conductors..

 

[betty swollocks]

For PME the size of the main protective bonding conductors need to be selected in line with table 54.8 (all sizes are given for copper cables) ;

TN-CS supply

CSA of the supply neutral Minimum CSA of MPB conductor

≤35mm

 

[MARTISPARKY]

the main earthing conductor will be 16mm and the tails are 25mm double insulated..so i know thats fine...i think i'll put it down in the observations and recommendations sheet as a 4... thanks for your info...

 

[extension15]

6mm main bonding conductors is perfectly acceptable (minimum) on TN supplies (existing)...

 

[green-hornet]

I always upgrade the main bonding to 10mm if changing consumer unit.

 

[ian932]

6mm main bonding conductors is perfectly acceptable (minimum) on TN supplies (existing)...

Which regulation says it is acceptable?? Section 544 does allow a minimum of 6mm, but as this is 16mm main earth then as section 544 states the protective bonds need to be 'not less than half the cross-sectional area required for the earthing conductor of the installation' . Therefore 10mm is what is need with a 25mm supply.

Don't forget these NIC guy's have committed the regs to memory and one thing they are going to trip you up on is earthing arrangements so don't take a gamble IMO doing it by the book for your major job is the only way to go.

Also as it is Part P work I dint see how you can fit a new CU without bring the main equipotential bonding up to code, the two go hand in hand.

They could throw stuff like this at you (Top of page 4) http://www.esc.org.uk/pdfs/business-and-community/electrical-industry/BPG1_08.pdf

 

[M107]

I'm with Ian, if the job is for your assessment then change to 10mm.

we all know that in the real world if it's a pain in the arris or customer will not stump up for extras (I always price main bond upgrade on a cu swap) the 6mm will suffice..

 

[MARTISPARKY]

thanks for all your replies, i guess i have to upgrade it then... its not the easiest of jobs and as it is in my own house it will be coming out of that ever so empty pocket of mine.... thanks guys...

 

[Nicky Tesla]

If the new board is fully rcd'd up then just like a TT system the 6mm will be more than adequate down to the adiabatic equation.

bonds need to be 'not less than half the cross-sectional area required for the earthing conductor of the installation' ......or like it says in all the books, use the adiabatic equation to see if you can use a smaller csa conductor for economic reasons.

For the equation The fault current will be just 30mA or possibly 60mA if both RCD where to trip at exactly same time (not much chance of that happening)

 

[berlingo2]

If the new board is fully rcd'd up then just like a TT system the 6mm will be more than adequate down to the adiabatic equation.bonds need to be 'not less than half the cross-sectional area required for the earthing conductor of the installation' ......or like it says in all the books, use the adiabatic equation to see if you can use a smaller csa conductor for economic reasons.

For the equation The fault current will be just 30mA or possibly 60mA if both RCD where to trip at exactly same time (not much chance of that happening)

For a PME system the minimum csa of a main bonding conductor should be selected from table 54.8 on page 134 of 7671 no less than 10mm, but remember that the resistance of a bonding conductor should be less than 0.05 ohms.

The adiabatic equation is for calculating main earthing conductor or cpc, not bonding conductors.

The new 17th edition consumer units are pre wired so that both RCD units will not trip at the same time.( the whole point of using a 17th board and splitting up circuits as per reg 314.1 on page 39)

Also 6mm bonding is not adequate for changing a consumer unit as per reg 131.8 on page 16.

Hope this helps.

 

[springcrocus]

Just to be awkward, if the main supply fuse is 60A and the tails are in 16mm, then it is satisfactory to use a 10mm main earthing conductor and 6mm bonding conductors.

There is no requirement to upgrade the tails to 25mm AFAIK.

What am I missing here?

 

[ElectekAir]

If you are installing a new consumer unit then you cant do a periodic and the NIC say you need to check the main bonding and earthing conductors before you change the CU.

I had this problem with them 6 years ago when i first joined them so you will have 2 problems and he will say thank you you will need to rectify the faults and book anouther visit

Craig

 

[Andy™]

If you are installing a new consumer unit then you cant do a periodic and the NIC say you need to check the main bonding and earthing conductors before you change the CU.I had this problem with them 6 years ago when i first joined them so you will have 2 problems and he will say thank you you will need to rectify the faults and book anouther visit

Craig

but they should be assessing your work to 7671, not their own version

 

[Nicky Tesla]

quote from berlingo above....The new 17th edition consumer units are pre wired so that both RCD units will not trip at the same time.( the whole point of using a 17th board and splitting up circuits as per reg 314.1 on page 39)

yes agreed, but it will not stop both RCD's tripping at the same time if there are two faults on seperate ccts at exactly the same time. As i said above not much chance of that happening.

Bonding cables exist to minimise the touch voltage between conductive and extraneous parts etc etc. They do this by keeping the voltage between parts below 50v, that is their job. Now if all the ccts in the house are protected by an rcd, then a max of 30mA could be flowing through any conductor be it conductive or extraneous. Therfore why on earth do we need bonding cables of 10mm in this situation really. What is the Prospective maximum current to pass through a bonding cable.

In fact any cpc on the whole system.....For me all the t&e cables should be fine with just 1.0mm cpc even 10mm.

 

[Nicky Tesla]

If you are installing a new consumer unit then you cant do a periodic and the NIC say you need to check the main bonding and earthing conductors before you change the CU.I had this problem with them 6 years ago when i first joined them so you will have 2 problems and he will say thank you you will need to rectify the faults and book anouther visit

Craig

I have read it somewhere ( i can't recall just now) that if the 6mm bonding does not show signs of any heat damage, then it will be fine.