Domestic Bonding test results has o.oo resistance on a 4mm cable do i still upgrade!

[TeeJay711]

Continuity test results from the board to the isolation valve to the house and from the board to the nearest radiator has o.oo resistance on a 4mm cable do i still have to upgrade to a 10mm.
It means ripping up the floor and kitchen units in the kitchen and laminate in the hallway to put in a cable that will still give me 0.0 results.

 

[HappyHippyDad]

Re: Domestic Bonding test results has o.oo resistance on a 4mm cable do i still upgra

all depends on the earthing arrangements, TNC-S you need 10mm. TN-S and TT systems, use adiabatic to determine the min. size.

yes, by association. use adiabatic to determine the min. size for the main earth, then ensure bonding conductor/s is/are at least 50% of the csa of the main earthing conductor.

I realise this thread is a few months old but it was similar to one I was going to start.

May as well be bluntly honest, I am trying to avoid putting in new main bonding for a CU change as the chap wont accept the job if the bonding has to be upgraded.

It a TT with 4mm Main Earthing and 4mm Main bonding.

The OSG states 6mm minimum for main bonding on a TT (which I cant quite get my head around if 2.5mm is ok for main earthing), but after reading Tel's posts above I am wondering if a lower csa is acceptable if it meets the adiabatic and is at least half of the Main earthing?

 

[ackbarthestar]

Re: Domestic Bonding test results has o.oo resistance on a 4mm cable do i still upgra

I realise this thread is a few months old but it was similar to one I was going to start.

May as well be bluntly honest, I am trying to avoid putting in new main bonding for a CU change as the chap wont accept the job if the bonding has to be upgraded.

It a TT with 4mm Main Earthing and 4mm Main bonding.

The OSG states 6mm minimum for main bonding on a TT (which I cant quite get my head around if 2.5mm is ok for main earthing), but after reading Tel's posts above I am wondering if a lower csa is acceptable if it meets the adiabatic and is at least half of the Main earthing?

The adiabatic equation is there to calculate the worst case fault current and usually associated with shared cpcs found in metalwork. You would then size the MPB conductor to half that size for anything other than PME systems, to a minimum of 6.0mm2.

Now an earthing conductor has a different function to a MPB conductor. The former is there to clear earth faults within the installation within the specified maximum allowable time from table 41.1 which will comply with the other tables in part 4 , 41.2, 41.3, 41.4 etc;

the latter is there to provide protection against external faults keeping the metalwork in the installation at an equal potential. It also aids protection by reducing the R2 of a faulted circuit and thus reducing the potential difference on any metalwork connected to the MET.

 

[telectrix]

Re: Domestic Bonding test results has o.oo resistance on a 4mm cable do i still upgra

if this were my job and the adiabatic confirmed that the MEC was adequate, and both MEC and MBC's showed no sign of damage, client refuses to pay for upgrade of these on a CU change, i'd go ahead with the CU, but make sure it's noted in the comments box that the earthing and bonding is not up to current standards. at the end of the day, you are making the installation safer than before, and also testing the circuits as to be safe for continued use, fixing any faults as part of the CU change.

 

[Richard Burns]

Re: Domestic Bonding test results has o.oo resistance on a 4mm cable do i still upgra

I would also specify that the upgrade of the bonding to meet the requirements of the regulations has been refused by the customer, but that the MPB does meet the requirements of csa when considered in relation to the minimum earthing conductor csa.

 

[Pete999]

Re: Domestic Bonding test results has o.oo resistance on a 4mm cable do i still upgra

What sort of test equipment is he using???????

 

[telectrix]

Re: Domestic Bonding test results has o.oo resistance on a 4mm cable do i still upgra

has he got it set to IR range?

 

[Pete999]

Re: Domestic Bonding test results has o.oo resistance on a 4mm cable do i still upgra

My thoughts also, a low range Ohmmeter would sureky give some other reading that 0.00 Ohms
Pete999

- - - Updated - - -

Surely even
Pete999

 

[alanl]

Re: Domestic Bonding test results has o.oo resistance on a 4mm cable do i still upgra

The main protective bonding sizes are quite clear in the Regs.
However, GN8 goes into detail how a smaller sized MPB can be re-used (not newly fitted) if certain conditions are met.
This has to be recorded in 'Departures from 7671' and 'Comments on existing Installation'.
Being as the minimum size of MPB has been 6mm for a long time (10mm has been typical for what, 18 years?), I wouldn't consider 4mm to be adequate, so would definitely upgrade it.
If it was already 6mm, then I may re-use it in limited circumstances, if, the Guidance Notes are adhered to.

 

[James Ingrem]

Re: Domestic Bonding test results has o.oo resistance on a 4mm cable do i still upgra

hey...bs7671 states 10mm for main bonding, tnc/tncs, stick with the regs to be safe

 

[shagbite]

Re: Domestic Bonding test results has o.oo resistance on a 4mm cable do i still upgra

hey...bs7671 states 10mm for main bonding, tnc/tncs, stick with the regs to be safe

not as catchy as "yah mo b there".

 

[davethsparky]

Re: Domestic Bonding test results has o.oo resistance on a 4mm cable do i still upgra

hey...bs7671 states 10mm for main bonding, tnc/tncs, stick with the regs to be safe

Really, what about the bit that has 6mm as the minimum size main bond for supplies other than TNCS?

Don't be a sheep and just follow all the other sheep, read the books and use your brains ability for independant thought!

 

[dcwuk]

Re: Domestic Bonding test results has o.oo resistance on a 4mm cable do i still upgra

I expect he is using his megger range on his meter not ohms:wink5: